,common ,m9]als & ,rocks ---------------------------------------- -------------------------------- ,bo/on ,society ( ,natural ,hi/ory ,,guides ,,= ,,sci5ce-,,tea*+ ,,no4 ,,xii ,,common ,,m9]als ,,& ,,rocks ,,by ,,william ,o4 ,,crosby ,d4 ,c4 ,,hea? ,,co41 ,,publi%]s ,,bo/on ,,new ,,york ,,*icago ---------------------------------------- -------------------------------- ,copyright ,,by ,,! ,,bo/on ,,society ,,( ,,natural ,,hi/ory #ahha ,i ,d #b ---------------------------------------- -------------------------------- ,,introduction4 ,illu/ration ,m9]als & rocks1 or ! inorganic portions ( ! e>?1 con/itute ! prop] field or subject-matt] ( ! sci5ce ( ,geology4 ,n[ ! inorganic e>?1 l an animal or plant1 may be & is /udi$ 9 ?ree q di/9ct ways1 giv+ rise to ?ree great divisions ( geology1 :i*1 z w be se51 correspond closely to ! ma9 divisions ( ,biology4 ,fir/1 we may /udy ! =ces n[ op]at+ ^u & 9 ! e>?--! geological ag5cies--su* z ! ocean & atmosph]e1 riv]s1 ra9 & fro/s1 e>?quakes1 volcanoes1 hot spr+s1 etc41 & obs]ve ! v>i\s effects :i* !y produce4 ,we are conc]n$ "h ) ! dynamics ( ! e>?2 & ?is is ! great division ( dynamical geology1 correspond+ to physiology among ! biological sci5ces4 ,or1 second1 in/ead ( geological causes1 we may /udy m p>ticul>ly geological effects1 obs]v+ ! diff]5t k9ds ( rocks & ( rock-/ructure produc$ by ! geological ag5cies1 n only at ! pres5t "t1 b also dur+ pa/ ages4 ,?is me?od ( /udy gives u ! important division ( /ructural geology1 correspond+ to anatomy & morphology4 ,all ph5om5a pres5t two di/9ct & opposite aspects or phases :i* we call cause & effect2 & s 9 dynamical & /ructural geology we are really /udy+ ! opposite sides ( ess5tially ! same classes ( ph5om5a4 ,9 ! fir/ division we /udy ! causes n[ 9 op]ation & obs]ve _! effects2 & !n1 guid$ by ! light ( ! exp]i5ce ?us ga9$1 we turn to ! effects produc$ 9 ! pa/ & seek to ref] !m to _! causes4 ,^! two divisions toge!r con/itute :at is prop]ly kn[n z physiography2 & !y are bo? subord9ate to ! ?ird great division ( geology1--hi/orical geology1--:i* corresponds to embryology4 ,! great object ( ! geologi/ is1 by /udy+ ! geological =mations 9 regul> ord]1 f ! olde/ up to ! newe/1 to "w out1 9 _! prop] sequ5ce1 ! ev5ts :i* con/itute ! e>?'s hi/ory2 & dynamical & /ructural geology are m]ely introductory *apt]s1 ! alphabet1 z x 71 :i* mu/ be le>n$ be=e we are prep>$ to read und]/&+ly ! gr& /ory ( ! geological record4 ,our "w 9 ?is %ort c\rse w be limit$ to ! fir/ two divisions1--i4e41 to dynamical & /ructural geology4 ,we w attempt1 fir/1 a g5]al sket* ( ! =ces n[ conc]n$ 9 ! =mation ( rocks & rock-/ructures2 & aft] t we w /udy ! composition & o!r *>act]i/ics ( ! common m9]als & rocks4 ,! scope ( ?is "w1 & its relations to ! :ole field ( geology1 are m cle>ly indicat$ by ! foll[+ classification ( ! geological sci5ces3-- ,,dynamical ,,geology ,physical ,geology4 ,*emical ,geology4 ,,geology ,,/ructural ,,geology ,m9]alogy4 ,petrography ,li?ology4 ,petrology4 ,,hi/orical ,,geology4 ,_m tea*]s w desire to fill 9 "s ( ! details ( ! outl9e sket* pres5t$ 9 ?is ,guide1 & = ?is purpose ! foll[+ works are especially recomm5d$3-- ,,elem5ts ,,( ,,geology4 ,by ,pr(4 ,joseph ,le ,conte4 #ahhb4 ,d4 ,appleton ,co41 ,new ,york4 ,ne>ly #fjj pages4 ,,manual ,,( ,,geology4 ,by ,pr(4 ,j4 ,d4 ,dana4 ,?ird edition4 #ahhj4 #hjj pages4 ,,text-,,book ,,( ,,geology4 ,by ,pr(4 ,a4 ,geikie4 #ahhb4 ,macmillan ,co41 ,london4 ,ne>ly #ajjj pages4 ,z a ref]5ce-book = m9]alogy1 ! foll[+ treatise is unsurpass$3-- ,,text-,,book ,,( ,,m9]alogy4 ,by ,edw>d ,s4 ,dana4 #ahhc4 ,john ,wiley ,sons1 ,new ,york4 ,&1 z an introduction to ! /udy ( m9]als1 &1 ?r\gh ^!1 to ! /udy ( rocks1-- ,,fir/ ,,lessons ,,9 ,,m9]als4 ,sci5ce ,guide ,no4 ,,xiii4 ,by ,mrs4 ,e4 ,h4 ,ri*>ds4 _c be too highly recomm5d$4 ,tea*]s w f9d ?is little prim] ( #df pages invaluable ) "y *ildr51 & ) all :o h _h no previ\s tra9+ 9 *emi/ry4 ,z an admirable cont9uation ( ! "w begun 9 ^! pages1 tea*]s are ref]r$ to ,pr(essor ,%al]'s 8,fir/ ,book 9 ,geology40 ,9 ?is our brief sket* ( ! geological ag5cies is amplifi$ & beautifully illu/rat$2 & r>ely h ! wond]ful /ories ( ! riv]1 ocean-bea*1 glaci]1 & volcano be5 told s effectively4 ,9 ! *apt] on ! hi/ory ( life on ! globe ! ma9 outl9es ( hi/orical geology are skillfully br\ght )9 ! compreh5sion ( beg9n]s4 ,! directions to tea*]s are fully 9 accord ) ! mod]n me?ods & ideas1 & are a v valuable feature ( ! book4 ---------------------------------------- -------------------------------- ,,dynamical ,,geology4 ,illu/ration ,:5 we ?9k ( ! ocean ) its waves1 tides1 & curr5ts1 ( ! w9ds1 & ( ! ra9 & sn[1 & ! va/ net-"w ( riv]s to :i* !y give rise1 we realize t ! en]gy or =ce manife/$ ^u ! e>?'s surface resides *iefly 9 ! air & wat]--9 ! e>?'s fluid envelope & n 9 its solid cru/4 ,& x w\ld be an easy matt] to %[ t1 ) ! exception ( ! tidal waves & curr5ts1 :i* ( c\rse are due *iefly to ! attraction ( ! moon1 ne>ly all ?is en]gy is m]ely ! trans=m$ heat ( ! sun4 ,n[ ! air & wat] are two great geological ag5cies1 & !re=e ! geological effects :i* !y produce are traceable back to ! sun4 ,organic matt] is ano!r important geological ag5t2 b all are famili> ) ! g5]alization t connects ! en]gy exhibit$ by e =m ( life ) ! sun2 &1 besides1 x is sc>cely necess>y to allude to ! obvi\s fact t all animals & plants1 s f> at lea/ z any display ( en]gy is conc]n$1 are m]ely diff]5tiat$ portions ( ! e>?'s fluid envelope4 ,& s1 if space p]mitt$1 x might be %[n t1 ) ! exception ( ! tides1 ne>ly e =m ( =ce manife/$ ^u ! e>?'s surface has its orig9 9 ! sun4 ,( ?is trio ( geological ag5cies op]at+ ^u ! e>?'s surface & vitaliz$ by ! sun--wat]1 air1 & organic matt]--! wat] is by f> ! mo/ important1 & s x is common to call ^! collectively ! aque\s ag5cies4 ,h5ce we h sol> ag5cies & aque\s ag5cies z synonym\s t]ms4 ,! aque\s ag5cies include1 on "o side1 air & wat]1 or inorganic ag5cies2 &1 on ! o!r1 animals & plants1 or organic ag5cies4 ,let u notice briefly ! op]ation ( ^!1 beg9n+ ) ! air & wat]4 ,i4 ,,aque\s ,,ag5cies4 #a4 ,air & ,wat]1 or ,inorganic ,ag5cies4 ,,*emical ,,erosion4--,att5tion is invit$ fir/ to ! specim5s numb]$ #a1 #b1 #c1 & #d4 ,no4 #a is a s\nd1 fre% piece ( ! r common rock1 diabase2 & ^? :o are acqua9t$ ) m9]als w recognize t ! light-color$ gra9s 9 ! rock are feldsp>1 & ! d>k1 augite4 ,?is specim5 came f a dep? 9 ! qu>ry1 & has n be5 expos$ to ! action ( ! wea!r4 ,! second specim5 diff]s f ! fir/1 app>5tly1 z mu* z possible2 & yet1 except 9 be+ some:at f9] gra9$1 x 0 orig9ally ( precisely simil> composition & appe>ance4 ,9 fact1 x is a portion ( ! same rock1 b a wea!r$ portion4 ,9 ?is we c no long] recognize ! feldsp> & augite z su*1 b bo? ^! m9]als are v mu* *ang$1 :ile 9 ! place ( a /rong1 h>d rock we h an incoh]5t friable mass1 :i* is1 ext]nally at lea/1 easily cru%$ to p[d]2 & ) ! next /ep 9 ! wea!r+1 z we may readily obs]ve 9 ! natural l$ges1 ! rock is completely dis9tegrat$1 =m+ a loose e>? or soil4 ,we h two examples ( su* natural p[d]s 9 ! specim5s numb]$ #c & #d2 & by wa%+ ^! 7especially ! f9] "o1 ,no4 #d7 ) wat]1 we c prove t !y consi/ ( an impalpable sub/ance :i* we may call clay1 & angul> gra9s :i* we may call s&4 ,! s&-gra9s are really portions ( ! feldsp> n yet entirely *ang$ to clay4 ,?us we le>n t ! result ( ! exposure ( ?is h>d rock to ! wea!r is t x is r$uc$ to ! condition ( s& & clay4 ,:at we mean especially by ! wea!r are moi/ure & c]ta9 con/itu5ts ( ! air1 p>ticul>ly c>bon dioxide4 ,! action ( ! wea!r on ! rocks is almo/ entirely *emical4 ,) a v few exceptions1 ! pr9cipal m9]als ( :i* rocks are compos$1 su* z feldsp>1 hornbl5de1 augite1 & mica1 are silicates1 i4e41 consi/ ( silicic acid or silica comb9$ ) v>i\s bases1 especially alum9um1 magnesium1 iron1 calcium1 potassium1 & sodium4 ,n[ ! silica does n hold all ^! bases ) equal /r5g?2 b c>bon dioxide1 9 ! pres5ce ( moi/ure1 is able to take ! sodium1 potassium1 calcium1 & magnesium away f ! silica 9 ! =m ( c>bonates1 :i*1 be+ soluble1 are c>ri$ away by ! ra9-wat]4 ,! silicate ( alum9um1 ) m or less iron1 takes on wat] at ! same "t1 & rema9s beh9d z a s(t1 impalpable p[d]1 :i* is common clay4 ,9 ! case ( our diabase1 cont9u$ exposure to ! wea!r w\ld r$uce ! :ole mass to clay4 ,b o!r rocks conta9 gra9s ( qu>tz1 a h>d m9]al :i* _c be decompos$1 & x always =ms s&4 ,c]ta9 classes ( rocks1 too1 su* z ! lime/ones & "s iron-ores1 are completely dissolv$ by wat] hold+ c>bon dioxide 9 solution1 & no?+ is left to =m soil1 except usually a small proportion ( insoluble impurities l s& or clay4 ,let u see next h[ ^! ag5ts ( decay get at ! rocks4 ,nei!r wat] nor air c p5etrate ! solid rock or m9]al to any consid]able ext5t1 s t practically ! action is limit$ to surfaces1 & :atev] multiplies surfaces mu/ favor decomposition4 ,fir/1 we h ! upp] surface ( ! rock :]e x is b>e1 b m especially :]e x is cov]$ ) soil1 = !re x is always wet4 ,all rocks are naturally divid$ by jo9ts into blocks1 :i* are frequ5tly m or less regul>1 & (t5 ( q small size4 ,wat] & air p5etrate into ^! cracks & decompose ! surfaces ( ! blocks1 & ?us ! field ( _! op]ations is enorm\sly ext5d$4 ,^! rock-blocks sometimes %[ v beautifully ! progress ( ! decompos+ ag5ts f ! outside inw>d by conc5tric lay]s or %ells ( rott5 mat]ial1 :i*1 9 ! l>g] blocks1 (t5 envelop a nucleus ( ! unalt]$ rock4 ,x is int]e/+ to obs]ve1 too1 t ^! conc5tric l9es ( decay cut (f ! angles ( ! orig9al blocks1 s t ! undecompos$ nucleus1 :5 x is f\nd1 is approximately sph]ical in/ead ( cuboidal4 ,bo? ^! po9ts are well illu/rat$ by specim5 ,no4 #b2 = al?\gh n[ ne>ly sph]ical1 x 0 orig9ally p]fectly angul>1 & has become r\nd$ by ! peel+ (f1 9 conc5tric lay]s1 ( ! decompos$ mat]ial1 & 9 mo/ cases sev]al ( ^! lay]s are di/9ctly visible1 l ! coats ( an onion4 ,b by /ripp+ ^! (f we %\ld discov]1 9 all ! l>g] balls at lea/1 a solid1 sph]oidal nucleus1 :ile 9 ! small] balls ! decomposition has p5etrat$ to ! c5tre4 ,9 ! rocks also we f9d _m imp]fect jo9ts & m9ute cracks4 ,9 cold c\ntries ^! are ext5d$ & wid5$ by ! expansive p[] ( freez+ wat]1 & ?us ! surfaces ( decomposition become con/antly great]4 ,ne>ly all rocks suff] ?is *emical decomposition :5 expos$ to ! wea!r1 b 9 "s ! decay goes on mu* fa/] ?an 9 o!rs4 ,diabase is "o ( ! rocks :i* decay mo/ readily2 :ile granite is1 among common rocks1 "o ( ^? t resi/ decay mo/ effectually4 ,! cav]ns :i* are s l>ge & num]\s 9 mo/ lime/one c\ntries are a spl5did example ( ! solv5t action ( meteoric wat]s1 be+ =m$ entirely by ! dissolv+ out ( ! lime/one by ! wat] circulat+ ?r\gh ! jo9t cracks4 ,! process mu/ g on ) extreme sl[ness at fir/1 :5 ! jo9ts are n>r[1 & m rapidly z !y are wid5$ & m wat] is admitt$4 ,we get "s idea1 too1 ( ! magnitude ( ! results accompli%$ by ^! sil5t & unobtrusive ag5cies :5 we reflect t almo/ all ! loose e>? & soil cov]+ ! solid rocks are simply ! insoluble residue :i* c>bon dioxide & wat] _c remove4 ,9 l[ latitudes1 :]e a w>m climate accel]ates ! decay ( ! rocks1 ! soil is usually f #ej to #cjj feet deep4 ,,me*anical ,,erosion4--,on ! edge ( ! l&4--,let u trace next ! me*anical action ( wat] & air ^u ! l&4 ,fir/ we w consid] ! edge ( ! l&1 :]e x is wa%$ by ! waves ( ! sea4 ,:oev] has be5 on ! %ore mu/ h notic$ t ! s& along ! wat]'s edge is kept 9 con/ant motion by ! ebb & fl[ ( ! surf4 ,:]e ! bea* is compos$ ( gravel or %+le ! motion is evid5t to ! e> z well z ! eye2 & :5 ! surf is /rong1 ! rattl+ & gr9d+ ( ! pebbles z !y are roll$ up & d[n ! bea* develops into a ro>4 ,! con/ant %ift+ ( ! gra9s ( s&1 pebbles1 & /ones is1 ( c\rse1 att5d$ by innum]able collisions1 :i* are ! cause ( ! noise4 ,n[ x is practically impossible1 z we may easily prove by exp]im5t1 to knock or rub two pieces ( /one toge!r1 at lea/ s z to produce mu* noise1 )\t abrad+ _! surfaces2 small p>ticles are deta*$1 & s& & du/ are =m$4 ,t ?is abrasion actually occurs 9 ! case ( ! mov+ s& is mo/ beautifully %[n by ! s&bla/4 ,we are to conclude1 !n1 t e "t a pebble1 l>ge or small1 is roll$ up or d[n ! bea* x becomes small]1 & "s s& & du/ or clay are =m$ :i* are c>ri$ (f by ! wat]4 ,b :at are ! pebbles orig9ally8 ,?is "q is n difficult4 ,a little obs]vation on ! bea* %[s u t ! pebbles are n all equally r\nd & smoo?1 b _m are m or less angul>4 ,& we soon see t x is possible to select a s]ies %[+ all gradations betwe5 ! mo/ p]fectly r\nd$ =ms & angul> fragm5ts ( rock t are only slightly abrad$ on ! corn]s4 ,! ?ree pr9cipal memb]s ( su* a s]ies are %[n 9 specim5s #e1 #f1 & #g f ! bea* on ,m>blehead ,neck2 b equally in/ructive specim5s c be obta9$ at _m o!r po9ts on our coa/4 ,x is also obs]vable t ! well-r\nd$ pebbles are mu* small] on ! av]age ?an ! angul> blocks4 ,f ^! facts we draw ! legitimate inf]5ce t ! pebbles 7 all orig9ally angul>1 & t ! same abrasion :i* dim9i%es _! size makes !m r\nd & smoo?4 ,a little reflection1 too1 %[s t ! r\nd+ ( ! angul> fragm5ts is a natural & necess>y result ( _! mutual collisions2 = ! angles are at ! same "t _! weake/ & mo/ expos$ po9ts1 & mu/ we> (f fa/] ?an ! flat or concave surfaces4 ,hav+ trac$ ea* pebble back to a l>g] angul> rock-fragm5t1 ! "q arises1 ,:5ce come ^! angul> blocks8 ,beh9d our gravel-bea*1 or at its end1 we h usually a cliff ( rocks4 ,z we approa* ?is x is di/9ctly obs]vable t ! angul> pebbles are m num]\s1 l>g]1 & m angul>2 & a little obs]vation %[s t ^! are simply ! blocks produc$ by jo9t+1 & t ! cliff is entirely compos$ ( !m4 ,9 o!r words1 our cliff is a mass ( natural masonry1 :i* *emical ag5cies1 ! fro/1 & ! sea are gradually dis9tegrat+ & remov+4 ,z soon z ! blocks are br\ght )9 rea* ( ! surf _! mutual collisions make !m r\nd] & small]2 & small r\nd pebbles1 s&1 & clay are ! f9al result4 ,= a m complete acc\nt ( ! =mation ( pebbles1 tea*]s are ref]r$ to ! fir/ or introductory numb] ( ?is s]ies ( guides1 by ,pr(4 ,hyatt1 8,ab\t ,pebbles40 ,:]e ! waves c drive ! %+le directly aga9/ ! base ( ! cliff1 ?is is gradually gr\nd away 9 ! same mann] z ! loose /ones !mselves1 sometimes =m+ a cav]n ( consid]able dep?1 b always leav+ a smoo?1 h>d surface1 :i* is v *>act]i/ic1 & contra/s /rongly ) ! upp] portion ( ! cliff1 :i* is act$ on only by ! ra9 & fro/4 ,a good example ( su* a pebble-c>v$ cliff may be se5 beh9d ! bea* on ! sea-w>d side ( ,m>blehead ,neck4 ,! sea acts )9 v n>r[ limits v]tically1 a few feet or a few y>ds at mo/2 b ! coa/-l9es ( ! globe 7includ+ inl& lakes & seas7 h an aggregate l5g? ( m ?an #aej1jjj miles4 ,h5ce x is easy to see t ! am\nt ( solid rock gr\nd to p[d] 9 ! mill ( ! ocean-bea* annually mu/ be v consid]able4 ,,me*anical ,,erosion4--,on ! surface ( ! l&4--,i next ask att5tion to ! me*anical action ( wat] ^u ! surface ( ! l&4 ,x is a famili> fact t aft] heavy ra9s ! roadside rills c>ry along mu* s& & clay 7:i* we "k h be5 produc$ by ! previ\s action ( *emical =ces71 & also frequ5tly small pebbles or gravel4 ,x is easy to %[ t 9 all important respects ! rill diff]s 9 size only f brooks & riv]s2 & ! =m] af=d u f9e models ( ! sy/ems ( valleys worn out dur+ ! lapse ( ages by riv]s4 ,! turbidity ( riv]s is (t5 v evid5t1 & 9 %all[ /reams we c sometimes see ! pebbles roll$ along by ! curr5t4 ,n[ "h1 j z on ! bea*1 ! collisions ( rock-fragm5ts are att5d$ by mutual abrasion1 s& & clay are =m$1 & ! fragm5ts become small] & r\nd]4 ,our s]ies ( pebbles f ! bea* might be mat*$ p]fectly among ! riv]-gravel4 ,9 m\nta9 /reams especially we may (t5 obs]ve t pebbles ( a p>ticul> k9d ( rock become m num]\s1 l>g]1 & m angul> z we proce$ up /ream1 until we rea* ! solid l$ge f :i* !y 7 d]iv$1 %[+ ! same gradation z ! bea* pebbles :5 foll[$ back to ! p>5t cliff4 ,! pebbles1 h[ev]1 n only gr9d ea* o!r1 b also ! solid rocks :i* =m ! b$ ( ! /reams 9 _m places1 & ^! are gradually worn away4 ,:5 ! rocky b$ is unev5 & ! wat] is swift1 pebbles collect 9 holl[s :]e eddies are =m$1 by :i* !y are kept :irl+ & turn+1 & ! holl[ is deep5$ to a pot-hole1 :ile ! pebbles1 ! riv]'s tools1 are worn out at ! same "t4 ,by ^! obs]vations we le>n n only t runn+ wat] c>ries away s& & clay already =m$1 b t x also has great p[] ( gr9d+ d[n h>d rocks to s& & clay4 ,( c\rse ! pulv]iz$ rock always moves 9 ! same direction z ! /ream :i* c>ries x2 &1 9 a c]ta9 s5se1 all /reams run 9 "o direction1 viz41 t[>d ! sea4 ,!re=e ! con/ant t5d5cy ( ! ra9 fall+ ^u ! l& is to break up ! rocks by *emical & me*anical action & transport ! dbris to ! sea4 ,riv]s1 z we all "k1 are cont9ually unit+ to =m l>g] & l>g] /reams2 & ?us ! dra9age ( a wide area sometimes1 z 9 ! case ( ! ,mississippi ,valley1 rea*es ! sea ?r\gh a s+le m\?4 ,by c>eful measurem5ts made at ! m\? ( ! ,mississippi x has be5 %[n t ! #bj1jjj1jjj1jjj1jjj cubic feet ( wat] dis*>g$ into ! ,gulf ( ,mexico annually c>ries ) x no less ?an #g1ejj1jjj1jjj cubic feet ( s&1 clay1 & dissolv$ m9]al matt]2 & ?is1 spread ov] ! :ole ,mississippi bas91 w\ld =m a lay] a little m ?an #a_/ejjj ( a foot 9 ?ickness4 ,s t we may conclude t ! surface ( ! cont95t is be+ cut d[n on ! av]age ab\t "o foot 9 five ?\s& ye>s4 ,we c only allude 9 pass+ to ! v important geological action ( wat] 9 ! solid /ate1 z 9 glaci]s & iceb]gs4 ,! moi/ure precipitat$ f ! atmosph]e1 & fall+ z ra91 makes ord9>y riv]s2 b fall+ 9 ! =m ( sn[ 9 cold regions1 :]e m sn[ falls ?an is melt$1 ! excess accumulates & is gradually compact$ to ice1 :i*1 l wat]1 yields to ! enorm\s pressure ( its own mass & fl[s t[>d l[] levels4 ,:5 ! ice-riv] rea*es ! sea x breaks (f 9 huge blocks1 :i* float away z iceb]gs4 ,mov+ ice1 l mov+ wat]1 is a p[]ful ag5t ( erosion2 & ! glacial m>ks or scrat*es obs]vable ^u ! l$ges ev]y:]e 9 ! ,nor!rn ,/ates & ,canada atte/ ! magnitude ( ! ice-action at a comp>atively rec5t p]iod4 ,we h already notic$ incid5tally ! p[]ful dis9tegrat+ action ( wat] :]e x freezes 9 ! jo9ts & pores ( ! rocks2 & x is probable t x ?us facilitates ! de/ruction ( ! rocks 9 cold c\ntries ne>ly z mu* z ! high] temp]ature & great] ra9-fall d 9 w>m c\ntries4 ,our obs]vations up to ?is po9t %[ u t erosion1 by :i* we mean ! break+ up by *emical & me*anical action ( ! rocks ( ! l& & ! transportation ( ! dbris into ! sea1 is "o great result accompli%$ by ! inorganic aque\s ag5cies4 ,,me*anical ,,deposition4--,next let u notice :at becomes ( all ?is va/ am\nt ( clay1 s&1 & gravel aft] x is wa%$ into ! ocean4 ,by tak+ up a glass ( turbid wat] f our roadside rill1 & obs]v+ t z soon z ! wat] is undi/urb$ ! s& & clay beg9 to settle1 we le>n t ! solid matt] is held 9 susp5sion by ! motion ( ! wat]4 ,b x does n rema9 9 susp5sion long aft] be+ wa%$ into ! sea1 = o!rwise ! sea w\ld1 9 ! c\rse ( "t1 become turbid = long di/ances f %ore2 & x is a well-kn[n fact t ! sea-wat] is usually cle> & free f s5sible turbidity close along %ore & ev5 ne> ! m\?s ( l>ge riv]s1 :ile at a di/ance ( only #ej or #ajj miles we f9d ! transp>5cy ( ! c5tral ocean4 ,putt+ ^! facts toge!r1 we see t ! ocean1 no?)/&+ ! ceaseless & (t5 viol5t undulations ( its surface1 mu/ be z a :ole a va/ body ( /ill wat]2 & to ! reflect+ m9d ! almo/ p]fect tranquillity ( ! ocean is "o ( its mo/ impressive features4 ,= x is 9 /rik+ contra/1 9 ?is respect1 ) ! m mobile a]ial ocean above x4 ,we h got hold1 n[1 ( two facts ( great geological importance3 7#a7 ,! dbris wa%$ (f ! l& by waves & riv]s into ! /ill wat] ( ! ocean v soon settles to ! bottom2 & 7#b7 x ne>ly all settles on t "p ( ! ocean-floor ne> ! l&4 ,& n[ we h 9 view ! second great (fice ( ! inorganic aque\s ag5cies1--deposition1 ! c\nt]p>t or complem5t ( erosion4 ,! l& is ! great !atre ( erosion & ! sea ( deposition2 ! rocks :i* are con/antly wa/+ away on ! =m] are z con/antly r5ew$ 9 ! latt]4 ,we w n[ obs]ve ! process ( deposition a little m closely4 ,ea* ( ^! two bottles conta9s ! same am\nt ( f9e yell[ clay1 b 9 "o ! wat] is fre%1 & 9 ! o!r x is salt4 ,at ! beg9n+ ( ! lesson1 z y may h obs]v$1 ,i br\ght ! clay 9 bo? bottles into susp5sion by viol5t agitation1 & s9ce !n !y h rema9$ undi/urb$4 ,! ma9 po9t is t ! salt wat] has become q cle>1 :ile ! fre% wat] is /ill di/9ctly turbid1 %[+ t ! salt favors ! rapid deposition ( ! clay4 ,at ! second lecture1 a week lat]1 ^! two bottles1 yet undi/urb$1 7 exhibit$1 & ! fre% wat] se5 to be /ill s5sibly turbid4 ,! fact is1 ! clay is n held 9 susp5sion :olly by ! motion ( ! wat]2 b1 j z 9 ! case ( du/ 9 ! atmosph]e1 a small portion ( ! m$ium is cond5s$ ar\nd or adh]es to ea* solid p>ticle1 i4e41 ea* clay p>ticle 9 our exp]im5t has an atmosph]e ( wat] :i* moves ) x & buoys x up4 ,n[ ! effect ( ! salt is to dim9i% ! adhesion ( ! wat] to ! p>ticles1 i4e41 to dim9i% _! atmosph]es1 & consequ5tly _! buoyancy4 ,! dim9i%$ adhesion ( ! salt wat] is well %[n by ! small] drops :i* x =ms on a glass rod4 ,! geological importance ( ?is pr9ciple is v great2 = x is und\bt$ly l>gely to ! saltness ( ! sea t we owe its transp>5cy1 & ! fact t ! f9e1 clayey s$im5t f ! l&1 l ! co>se1 is deposit$ ne> ! %ore4 ,?is bottle ( fre% wat] conta9s "s f9e gravel1 co>se s&1 f9e s&1 & clay4 ,by agitat+ ! wat]1 all ?is mat]ial is br\ght into susp5sion4 ,n[1 sudd5ly plac+ ! bottle 9 a /ate ( re/1 we obs]ve t ! gravel falls to ! bottom almo/ in/antly1 foll[$ quickly by ! co>se s&1 & v soon aft]w>d by ! f9e s&2 & !n !re appe>s to be a pause1 ! f9e p>ticles ( clay all rema9 9 susp5sion2 b f9ally1 :5 ! wat] is q motionless1 !y beg9 to settle2 !y fall v sl[ly1 h[ev]1 & ! wat] w n be cle> = h\rs4 ,?is is a v in/ructive exp]im5t4 ,we le>n f x3 ,fir/1 t ! p[] ( ! wat] to hold p>ticles 9 susp5sion is inv]sely proportional to ! size ( ! p>ticles2 ,second1 t all mat]ials deposit$ 9 wat] are assort$ accord+ to size2 ,?ird1 & ?is is "o ( ! mo/ important facts 9 geology1 all wat]-deposit$ s$im5ts are arrang$ 9 horizontal lay]s1 i4e41 are /ratifi$4 ,& we h n[ trac$ to its conclusion1 ?\gh v briefly1 ! process ( ! =mation ( "o great division ( /ratifi$ rocks1--! me*anically-=m$ or fragm5tal rocks4 ,^! are s call$ because ! clay1 s&1 & gravel are1 9 e in/ance1 fragm5ts ( pre-exi/+ rocks2 & because ! =mation1 transportation1 & especially ! deposition ( ^! fragm5ts1 are ! "w *iefly or entirely ( me*anical =ces4 ,,*emical ,,deposition4--,x is a well-kn[n fact t ! sea holds 9 solution va/ am\nts ( common salt z well z _m o!r sub/ances2 & analyses ( riv]-wat]s %[ t dissolv$ m9]als d]iv$ f ! *emical decomposition ( ! rocks ( ! l& are be+ con/antly c>ri$ into ! sea4 ,portions ( ! sea :i* are cut (f f ! ma9 body1 & :i* are gradually dry+ up1 l ! ,great ,salt ,lake1 ,dead ,sea1 & ,caspian ,sea1 become saturat$ solutions ( ! v>i\s dissolv$ m9]als1 & ^! are sl[ly deposit$4 ,?is process is v nicely illu/rat$ along our %ores 9 summ]1 :]e1 dur+ /orms1 salt-wat] spray is ?r[n above ! rea* ( ! tides1 &1 collect+ 9 holl[s 9 ! rocks1 gradually dries up1 leav+ beh9d a cru/ ( salt4 ,:5 ! sea lays d[n matt] :i* x held 9 susp5sion1 we call ! process me*anical deposition1 & ! result is me*anically-=m$ rocks4 ,b :5 x lays d[n matt] :i* x held 9 solution1 we call ! process *emical deposition1 & ! result is *emically-=m$ rocks4 ,! pr9cipal sub/ances :i* ! sea deposits *emically are common salt1 =m+ b$s ( rock-salt2 sulphate ( calcium1 =m+ b$s ( gypsum2 c>bonate ( calcium1 =m+ b$s ( lime/one2 & ! d\ble c>bonate ( calcium & magnesium1 =m+ b$s ( dolomite4 ,inorganic deposition1 l inorganic erosion1 is bo? *emical & me*anical4 #b4 ,animals & ,plants1 or ,organic ,ag5cies4 ,we turn n[ to ! consid]ation ( ! organic ag5cies4 ,& ,i w m]ely allude 9 pass+ to ! va/ importance ( ! fossil organic rema9s f\nd 9 ! /ratifi$ rocks z m>ks by :i* to det]m9e ! relative ages ( ! =mations4 ,z reg>ds ! de/ruction ( rocks--erosion--plants & animals are almo/ p[]less2 b 9 ! role ( rock-mak]s !y play a v important "p1 be+ v effici5t ag5ts ( deposition4 ,,=mation ,,( ,,coals ,,& ,,bitum5s4--,specim5 ,no4 #h is an example ( peat f ! vic9ity ( ,bo/on2 b j z good specim5s may be obta9$ 9 ?\s&s ( places 9 ?is & o!r ,/ates4 ,! g5]al physical conditions "u :i* peat is =m$ are famili> facts4 ,we require simply l[1 level l&1 cov]$ ) a ?9 %eet ( wat] & abundant vegetation2 9 o!r words1 a m>% or swamp4 ,if plants decay on ! dry l&1 ! decomposition is complete2 !y are burn$ up by ! oxyg5 ( ! air to c>bon dioxide & wat] j z surely z if !y _h be5 ?r[n into a furnace1 ?\gh less rapidly1 & no?+ is return$ to ! soil b :at _h be5 tak5 f x by ! plants dur+ _! gr[?4 ,b if ! plants decay "u wat]1 z 9 a peat-m>% or bog1 ! decay is incomplete1 & mo/ ( ! c>bon ( ! wood is left beh9d4 ,n[1 if ?is incomplete combu/ion ( vegetable tissues takes place 9 a *>coal-pit1 :]e ! wood is out ( contact ) air f be+ cov]$ ) e>?1 we call ! c>bonace\s product *>coal2 b if "u ! wat] ( a m>%1 9 ,nature's laboratory1 we call ! product peat4 ,peat is simply a natural *>coal2 &1 j z 9 ord9>y *>coal1 its vegetable orig9 is always p]fectly evid5t4 ,b :5 ! deposit becomes ?ick]1 & especially :5 x is buri$ "u ?ick =mations ( o!r rocks1 l s& & clay1 ! great pressure consolidates ! peat2 x becomes gradually m m9]aliz$ & %9+1 %[s ! vegetable tissues less di/9ctly1 becomes m ne>ly pure c>bon1 & we call x 9 succession lignite1 bitum9\s coal1 & an?racite4 ,?is is1 briefly1 ! way 9 :i* all v>ieties ( coal1 z well z ! m solid k9ds ( bitum51 l asphaltum1 are =m$4 ,b ! light] =ms ( bitum51 su* z petroleum & naph?a1 are d]iv$ ma9ly1 if n entirely1 f ! p>tial decomposition ( animal tissues4 ,^!1 x is well kn[n1 decay mu* m readily ?an vegetable tissues2 & ! wat] ( an ord9>y m>% or lake conta9s suffici5t oxyg5 = _! complete & rapid decomposition4 ,9 ! deep] p>ts ( ! ocean1 h[ev]1 ! conditions are v diff]5t1 = rec5t rese>*es h %[n1 contr>y to ! old idea1 t ! deep sea holds an abundant fauna4 ,all grades ( animal life1 f ! highe/ to ! l[e/1 h ne$ ( a con/ant supply ( oxyg54 ,on ! l& vegetation is con/antly return+ to ! air ! oxyg5 consum$ by animals1 b 9 ! abysses ( ! ocean vegetable life is sc>ce or want+2 & h5ce x mu/ result t ov] ^! great] ?an cont95tal areas c\ntless myriads ( animals are liv+ habitually on %ort rations ( oxyg51 & 9 wat] well *>g$ ) c>bon dioxide1 ! product ( animal respiration4 ,z a consequ5ce1 :5 ^! animals die _! tissues d n f9d ! oxyg5 ess5tial = _! p]fect decomposition1 & 9 ! c\rse ( "t become buri$1 9 a half-decay$ /ate1 9 ! ev]-increas+ s$im5ts ( ! ocean-floor4 ,x is important to obs]ve t an abundance ( organic matt] decay+ "u wat] is n ! only condition ess5tial to ! =mation ( b$s ( coal & bitum52 = ?is condition is realiz$ 9 ! luxuriant gr[? ( sea-we$s fr++ ! coa/ 9 e qu>t] ( ! globe2 & yet coals & bitum5s are r>ely ( sea-%ore orig94 ,^! organic products1 ev5 "u ! mo/ favorable circum/ances1 accumulate ) extreme sl[ness2 f> m sl[ly1 z a rule1 ?an ! ord9>y me*anical s$im5ts1 l s& & clay1 ) :i* !y are mix$1 & 9 :i* !y are (t5 completely lo/4 ,consequ5tly1 al?\gh ! deposition ( ! c>boniz$ rema9s ( plants & animals is tak+ place 9 ne>ly all seas1 lakes1 & m>%es1 x is only 9 ^? places :]e !re is little or no me*anical s$im5t t !y c pr$om9ate s z to build up b$s pure en\gh to be call$ coal or bitum54 ,9 all o!r cases we get m]ely m or less c>bonace\s s& or clay4 ,n[ ^! especially favorable localities w manife/ly n be (t5 f\nd along ! sea%ore1 :]e we h /rewn ! s& & clay br\ght d[n by riv]s or wa%$ (f ! l& directly by ! ev]-active surf2 b !y mu/ exi/ 9 ! c5tral portions ( ! ocean1 :]e !re is almo/ no me*anical s$im5t & yet an abundance ( life1 & 9 swamps & m>%es1 :]e !re is sc>cely suffici5t wat] to cov] ! vegetation1 & no waves or curr5ts to wa% d[n ! soil f ! surr\nd+ hills4 ,,=mation ,,( ,,iron-,,ores4--,! iron-ores are ano!r class ( rocks :i* are =m$ only ?r\gh ! ag5cy ( organic matt]4 ,iron is an abundant & wide-spread elem5t 9 ! e>?'s cru/1 &1 b = ! int]v5tion ( life1 we might say t1 :ile !re is iron ev]y:]e1 !re is n mu* ( x 9 any "o place1 s9ce x is orig9ally v ?9ly diffus$4 ,all rocks & soils conta9 iron1 b x is ma9ly 9 ! =m ( ! p]oxide1 9 :i* /ate x is entirely insoluble1 & h5ce _c be soak$ out ( ! soil by ! ra9-wat] & conc5trat$ by ! evaporation ( ! wat] at l[] levels 9 ponds & m>%es1 z a soluble sub/ance l salt w\ld be4 ,if c>ri$ (f ) ! s& & clay1 by ! me*anical action ( wat]1 x rema9s uni=mly mix$ ) !m1 & !re is no t5d5cy to its sep>ation & conc5tration s z to =m a true iron-ore4 ,b :at wat] _c d alone is accompli%$ v readily :5 ! wat] is aid$ by decay+ organic matt]1 :i* is always hungry = oxyg51 be+1 9 ! language ( ! *emi/1 a p[]ful r$uc+ ag5t4 ,! soil1 9 mo/ places1 has a sup]ficial /ratum ( vegetable m\ld or half-decay$ vegetation4 ,! ra9wat] p]colates ?r\gh ?is & dissolves m or less ( ! organic matt]1 :i* is ?us c>ri$ d[n into ! s& & clay b5ea? & br\ght 9 contact ) ! f]ric oxide1 f :i* x takes a c]ta9 proportion ( oxyg51 r$uc+ ! f]ric to ! f]r\s oxide4 ,at ! same "t ! vegetation is burn$ up by ! oxyg5 ?us obta9$1 =m+ c>bon dioxide1 :i* imm$iately comb9es ) ! f]r\s oxide1 =m+ c>bonate ( iron1 :i*1 be+ soluble "u ^! conditions1 is c>ri$ along by ! wat] z x gradually f9ds its way by subt]ranean dra9age to ! bottom ( ! valley & em]ges 9 a swamp or m>%4 ,"h "o ( two ?+s w happ53 ,if ! m>% conta9s little or no decay+ vegetation1 !n z soon z ! f]r\s c>bonate br\ght d[n f ! hills is expos$ to ! air x is decompos$1 ! c>bon dioxide escapes1 & ! iron1 tak+ on oxyg5 f ! air1 returns to its orig9al f]ric condition2 & be+ !n q insoluble1 x is deposit$ z a loose1 por\s1 e>?y mass1 commonly kn[n z bog-iron-ore1 :i* becomes gradually m solid & f9ally ev5 cry/all9e ?r\gh ! subsequ5t action ( heat & pressure4 ,:5 fir/ deposit$1 ! f]ric oxide is comb9$ ) wat] or hydrat$1 & is !n kn[n z limonite 7specim5 ,no4 #ab72 at a lat] p]iod ! wat] is expell$1 & we call ! ore hematite 7specim5 ,no4 #ac72 & at a /ill lat] age x loses "p ( its oxyg51 becomes magnetic & m cry/all9e1 & is !n kn[n z magnetite 7specim5 ,no4 #ad74 ,?us x is se5 t ! iron-ores1 z we pass f bog-limonite to magnetite1 =m a natural s]ies simil> to & p>allel ) t af=d$ by ! coals z we pass f peat to graphite4 ,if ! dra9age f ! hills is into a m>% conta9+ an abundance ( decay+ vegetation1 i4e41 if peat is =m+ !re1 ! f]r\s c>bonate1 9 ! pres5ce ( ! m gre$y organic matt]1 w be unable to obta9 oxyg5 f ! air2 & z ! evaporation ( ! wat] goes on1 x w soon] or lat] become saturat$ ) ?is salt1 & ! latt] w be deposit$4 ,"h we f9d an explanation ( a fact (t5 obs]v$ by geologi/s1 viz41 t ! c>bonate iron-ores are usually associat$ ) b$s ( coal4 ,! =mation ( ! iron-ores1 l t ( ! coals & bitum5s1 is a sl[ process2 & ! ores1 l ! coals1 etc41 w be pure only :]e !re is a complete abs5ce ( me*anical s$im5t1 a condition t is realiz$ mo/ ne>ly 9 m>%es4 ,,=mation ,,( ,,lime/one1 ,,diatomace\s ,,e>?1 ,,etc4--,m>9e animals take f ! sea-wat] c]ta9 m9]al sub/ances1 especially silica & c>bonate ( calcium1 to =m _! skeletons4 ,silica is us$ only by ! l[e/ organisms1 su* z ,radiol>ia1 ,sponges1 & ! m9ute unicellul> plants1 ,diatoms4 ,! pr9cipal animals secret+ c>bonate ( calcium are ,corals & ,mollusks4 ,^! h>d p>ts ( ! organisms rema9 undissolv$ aft] dea?2 & ov] portions ( ! ocean-floor :]e !re is b little ( o!r k9ds ( s$im5t !y =m ! ma9 "p ( ! deposits1 & 9 ! c\rse ( ages build up v ext5sive =mations :i* we call diatomace\s e>? or tripolite1 if ! organisms are silice\s1 or lime/one if !y are calc>e\s4 ,a v satisfactory acc\nt ( ! =mation ( lime/one on a /up5d\s scale by ! polyps 9 coral reefs & isl&s is conta9$ 9 ,no4 ,,iv4 ( ?is s]ies ( guides4 ,! rocks "h consid]$ may be1 &1 z we h already se51 sometimes are1 deposit$ 9 a purely *emical way1 )\t ! aid ( life2 & x is important to obs]ve t 9 no case d ! organisms make ! silica & c>bonate ( calcium ( _! skeletons1 b !y simply appropriate & r$uce to ! solid /ate :at exi/s ready made 9 solution 9 ! sea-wat]4 ,^! m9]als1 & o!rs1 z we "k1 are produc$ by ! decomposition ( ! rocks ( ! l&1 & are be+ con/antly c>ri$ into ! sea by riv]s2 &1 if !re 7 no animals 9 ! sea1 ^! processes w\ld /ill g on until ! sea-wat] became saturat$ ) ^! sub/ances1 :5 _! precipitation z lime/one1 etc41 w\ld necess>ily foll[4 ,h5ce x is cle> t all ! animals d is to effect ! precipitation ( c]ta9 m9]als some:at soon] ?an x w\ld o!rwise occur2 s t f a geological /&po9t ! diff]5ces betwe5 *emical & organic deposition are n great4 ,?is section ( our subject may be summ>iz$ z foll[s3 ,animals & plants contribute to ! =mation ( rocks 9 ?ree di/9ct ways3-- #a4 ,dur+ _! gr[? !y deoxidize c>bon dioxide & wat]1 & r$uce to ! solid /ate 9 _! tissues c>bon & ! p]man5t gases oxyg51 hydrog51 & nitrog52 & aft] dea?1 ?r\gh ! accumulation ( ! half-decay$ tissues 9 favorable localities1--m>%es1 etc41--^! elem5ts are add$ to ! solid cru/ ( ! e>? 9 ! =m ( coal & bitum54 #b4 ,dur+ ! decomposition1 i4e41 oxidation1 ( ! organic tissues1 ! iron exi/+ ev]y:]e 9 ! soil is p>tially deoxidiz$1 &1 be+ ?us r5d]$ soluble1 is remov$ by ra9-wat] & conc5trat$ 9 l[ places1 =m+ b$s ( iron-ore4 #c4 ,?r\gh ! ag5cy ( m>9e organisms1 c]ta9 m9]al sub/ances are be+ con/antly remov$ f ! sea-wat] & deposit$ ^u ! ocean floor1 =m+ v>i\s calc>e\s & silice\s rocks4 ,i n[ br+ our /udy ( ! aque\s or sup]ficial ag5cies to a conclusion by not+ once m t ! great geological results accompli%$ by air1 wat]1 & organic matt] or life are3 7#a7 ,erosion1 or ! we>+ away ( ! surface ( ! l&2 & 7#b7 ,deposition1 or ! =mation f ! dbris ( ! erod$ l& ( two great classes ( /ratifi$ rocks1--! me*anically =m$ or fragm5tal rocks1 & ! *emically & organically =m$ rocks4 ,,ii4 ,,igne\s ,,ag5cies4 ,we pass next to a v brief consid]ation ( op]ations t orig9ate bel[ ! e>?'s surface4 ,! records ( deep m9es & artesian wells %[ t ! temp]ature ( ! gr\nd always increases d[nw>ds f ! surface2 & ! mu* high] temp]atures ( hot spr+s & volcanoes %[ t ! heat cont9ues to increase to a great dep?1 & is n a m]ely sup]ficial ph5om5on4 ,! obs]v$ rate ( increase is n uni=m1 b x seldom v>ies f> f ! av]age1 :i* is ab\t #a ,fahr4 p] #ec feet ( v]tical desc5t1 or1 9 r\nd numb]s1 #ajj p] mile4 ,?is rate1 if cont9u$1 w\ld give a v high temp]ature at po9ts only a few miles bel[ ! surface2 & until )9 a few ye>s ! idea 0 g5]ally accept$ by geologi/s t ! increase ( temp]ature is s5sibly uni=m = an indef9ite di/ance d[nw>d2 t 9 ! c5tral regions ( ! e>? ! temp]ature is f> high] ?an any?+ we c conceive1 & t ev]y:]e bel[ a dep? ( #bj to #dj miles ! temp]ature is above ! fus+-po9t ( all rocks2 & h5ce t ! e>? is an inc&esc5t liquid globe cov]$ by a ?9 %ell or cru/ ( cold1 solid rock4 ,our limit$ space w n p]mit u to ent] into a discussion ( ! condition ( ! e>?'s int]ior1 & ,i w m]ely po9t out 9 a few s5t5ces ! position occupi$ by geologi/s at ! pres5t "t4 ,! reason+ ( ,?ompson has %[n t ! temp]ature _c increase d[nw>d at a uni=m rate1 b at a con/antly & rapidly dim9i%+ rate2 & t ev]y:]e bel[ a dep? ( #cjj miles ! temp]ature is probably s5sibly ! same1 & n[h]e1 probably1 above #hjjj to #aj1jjj ,fahr4 ,unlike wat]1 all rocks contract on solidify+ & exp& on melt+1 & consequ5tly ! high pressures to :i* !y are subject$ 9 ! e>?'s int]ior--#aj1jjj1jjj to #bj1jjj1jjj p\nds p] squ>e in*--mu/ raise _! fus+-po9ts enorm\sly1 & ! probabilities are t !y are solid1 9 spite ( ! high temp]ature4 ,b ,?ompson & ,d>w9 h %[n u f>!r t ! ph5om5a ( ! oceanic tides c\ld n be :at !y are kn[n to be if ! e>? 7 any less rigid ?an a globe ( solid /eel2 :ile ,hopk9s has prov$ t ! a/ronomical ph5om5a ( precession & nutation c\ld n be :at !y are if ! e>?'s cru/ 7 less ?an #hjj or #ajjj miles ?ick4 ,putt+ ^! consid]ations toge!r1 geologi/s are almo/ univ]sally agre$ t1 :ile ! e>? has an inc&esc5t int]ior1 x is /ill cont9u\sly solid f c5tre to circumf]5ce1 ) ! exception ( a ?9 pla/ic /ratum at a dep? n exce$+ #dj or #ej miles1 :i* =ms ! seat ( volcanic action4 ,! e>? is n only a v hot body1 b x is rotat+ ?r\gh almo/ absolutely cold space1 & !re=e mu/ be a cool+ body4 ,b1 except at ! v beg9n+ ( ! cool+1 ! loss ( heat has gone on almo/ entirely f ! int]ior2 & s9ce cool+ means contraction1 ! heat$ int]ior mu/ be con/antly t5d+ to %r9k away f ! cold ext]nal cru/4 ,( c\rse no actual sep>ation betwe5 ! cru/ & int]ior or nucleus c take place1 b !re is no d\bt t ! cru/ is left unsupport$ to a c]ta9 ext5t1 & x mu/ !n behave l an ar* ) a radius ( #djjj miles1 & ! result is an enorm\s horizontal or tang5tial pressure4 ,?is lat]al pressure 9 ! e>?'s cru/ is "o ( ! mo/ important & mo/ g5]ally accept$ facts 9 geology1 & lies at ! bottom ( _m geological !ories4 ,accord+ to :at seems to me to be ! mo/ probable !ory ( ! orig9 ( cont95ts & ocean-bas9s1 !y are broad upw>d & d[nw>d b5d+s or ar*es into :i* ! cru/ is ?r[n by ! tang5tial pressure4 ,f9ally1 ! /ra9 becomes great en\gh to cru% ! cru/ along ^? l9es :]e x is weake/4 ,:5 ! cru/ is ?us ma%$ up by horizontal pressure1 a m\nta9 range is =m$1 ! cru/ becomes enorm\sly ?ick]1 & a weak place becomes a /rong "o4 ,dur+ ! =mation ( m\nta9s ! /ratifi$ rocks1 :i* 7 orig9ally horizontal1 are ?r[n into folds or ar*es1 & tipp$ up at all possible angles2 !y are fractur$ & faults produc$2 & by ! imm5se pressure ! /ructure kn[n z slaty cleavage is develop$4 ,9 fact1 a va/ am\nt & v>iety ( /ructures are produc$ dur+ ! gr[? ( a m\nta9 range4 ,^! great e>?-movem5ts are n always p]fectly smoo? & /eady1 b !y are accompani$ by slipp+ or cru%+ n[ & !n2 &1 z a result ( ! %ock ?us produc$1 a swift vibratory movem5t or j>1 :i* we "k z an e>?quake1 runs ?r\gh ! e>?'s cru/4 ,ext5sive fissures are also =m$1 op5+ d[n to ! regions :]e ! rocks are liquid or pla/ic1 & ?r\gh ^! ! melt$ rocks fl[ up to or t[>d ! surface4 ,t portion :i* fl[s out on ! surface builds up a volcanic cone1 :ile t :i* cools & solidifies bel[ ! surface1 9 ! fissures1 =ms dikes4 ,?us among ! igne\s or eruptive rocks we h two great classes1--! dike rocks & ! volcanic rocks4 ,x is important to obs]ve t all ^! subt]ranean op]ations--! =mation ( cont95ts1 ( m\nta9-ranges ) all _! att5dant ph5om5a ( folds1 faults & cleavage1 & e =m & phase ( e>?quake & volcanic activity--dep5d ^u or orig9ate 9 ! int]ior heat ( ! e>?4 ,& ov] aga9/ ! sup]ficial or aque\s ag5cies1 orig9at+ 9 ! sol> heat & produc+ ! /ratifi$ or s$im5t>y rocks1 we set ! subt]ranean or igne\s ag5cies orig9at+ 9 ! c5tral heat1 & produc+ ! un/ratifi$ or eruptive rocks4 ---------------------------------------- -------------------------------- ,,/ructural ,,geology4 ,illu/ration ,9 geology1 j z 9 biology1 !re are two ways ( /udy+ /ructure1--! small way & ! l>ge way4 ,9 ! case ( an organism1 we may select a s+le "p or organ1 &1 disreg>d+ its ext]nal =m & relations to o!r p>ts1 obs]ve its composition & m9ute /ructure1 ! v>i\s =ms & arrangem5ts ( ! cells1 etc4 ,?is is hi/ology1 & x is ! complem5t ( t l>g] me?od ( /udy+ /ructure :i* is ord9>ily und]/ood by anatomy4 ,! divisions ( /ructural geology correspond+ to hi/ology & anatomy are li?ology & petrology4 ,li?ology is an 9-door sci5ce2 we use ! microscope l>gely1 & "w ) h& specim5s or ?9 sections ( ! rocks1 obs]v+ ! composition & ^? small /ructural features :i* g "u ! g5]al "n ( texture4 ,9 petrology1 on ! o!r h&1 we consid] ! l>g] k9ds ( rock-/ructure1 su* z /ratification1 jo9t+1 folds1 faults1 cleavage1 etc42 & x is ess5tially an out-door sci5ce1 s9ce to /udy x to ! be/ advantage we mu/ h1 n h& specim5s1 b l$ges1 cliffs1 railway-cutt+s1 gorges1 & m\nta9s4 ,,li?ology4 ,a rock is any m9]al1 or mixture ( m9]als1 occurr+ 9 masses ( consid]able size4 ,?is di/9ction ( size is ! only "o t c be made betwe5 rocks & m9]als1 & t is v indef9ite4 ,a rock1 :e!r compos$ ( "o m9]al or sev]al1 is always an aggregate2 & !re=e no s+le cry/al or m9]al-gra9 c prop]ly be call$ a rock4 ,be=e proce$+ to /udy p>ticul>ly ! v>i\s k9ds ( rocks1 a little m prelim9>y "w %\ld be done4 ,z already intimat$1 ! m important *>act]i/ics ( rocks may be gr\p$ "u two g5]al heads1--composition & texture4 ,composition ( ,rocks4 ,rocks are prop]ly def9$ z l>ge masses or aggregates ( m9]al matt]1 consi/+ 9 "s cases ( "o & 9 o!r cases ( sev]al m9]al species4 ,h5ce x is cle> t ! composition ( rocks is ( two k9ds3 *emical & m9]alogical2 = ! v>i\s *emical elem5ts are fir/ comb9$ to =m m9]als1 & !n ! m9]als are comb9$ to =m rocks4 ,( c\rse ^? m9]als & elem5ts :i* c be describ$ z pr9cipal or important rock-con/itu5ts mu/ be ! common m9]als & elem5ts4 ,n[ x is a v important & conv5i5t fact t al?\gh *emi/s recognize ab\t sixty-five elem5t>y sub/ances1 & ^! are comb9$ to =m ne>ly "o ?\s& m9]al species1 yet bo? ! common elem5ts & ! common m9]als are few 9 numb]4 ,s t1 al?\gh x is v desirable & ev5 necess>y = ! /ud5t ( li?ology to "k some?+ ( *emi/ry & m9]alogy1 x by no means foll[s t he or %e mu/ be ma/] ( ^? sci5ces4 ,a k ( ! *emical & physical *>act]i/ics ( a few common m9]als is all t is absolutely ess5tial1 ?\gh x may be add$ t an excess ( wisdom 9 ^! directions is no disadvantage4 ,*emical ,composition ( ,rocks4 ,! elem5t>y sub/ances ( :i* rocks are *iefly compos$1 :i* make up ! ma9 mass ( ! e>? s f> z we are acqua9t$ ) x1 numb] only f\rte53-- ,non-,metallic or ,acidic ,elem5ts4--,oxyg51 silicon1 c>bon1 sulphur1 *lor9e1 phosphorus1 & fluor9e4 ,metallic or ,basic ,elem5ts4--,alum9um1 magnesium1 calcium1 iron1 sodium1 potassium1 & hydrog54 ,! elem5ts are nam$ 9 ea* gr\p 9 ab\t ! ord] ( _! relative abundance2 & to give "s idea ( ! enorm\s diff]5ces 9 ?is respect x may be /at$ t two ( ! elem5ts--oxyg5 & silicon--=m m ?an half ( ! e>?'s cru/4 ,silicon1 calcium1 & fluor9e1 al?\gh exce$+ly abundant1 are also v difficult to obta9 9 ! free or uncomb9$ /ate1 & specim5s l>ge en\gh to exhibit to a class w\ld be v exp5sive4 ,) ^! exceptions1 h[ev]1 examples ( ^! common rock-=m+ elem5ts are easily obta9$4 ,my purpose 9 call+ att5tion to ?is po9t is simply to sugge/ t ! prop] way to beg9 ! /udy ( m9]als & rocks ) *ildr5 is to fir/ famili>ize !m ) ! elem5ts ( :i* !y are compos$4 ,! mo/ important ?+ to be kn[n ab\t any m9]al is its *emical composition2 & :5 a *ild is told t a m9]al--corundum1 = example--is compos$ ( oxyg5 & alum9um1 he %\ld h a di/9ct conception ( ! prop]ties ( ea* ( ^? elem5ts1 = o!rwise corundum is = him a m]e comp\nd ( names4 ,x is v important1 too1 if ! pupil has n already /udi$ *emi/ry1 t he %\ld be l$ to "s compreh5sion ( ! nature ( *emical union & ( ! diff]5ce betwe5 a *emical comp\nd & a me*anical mixture4 ,= ?is purpose a few simple exp]im5ts 7! details ( :i* w\ld be out ( place "h7 ) ! m common & famili> elem5ts w be suffici5t4 ,mrs4 ,ri*>d's 8,fir/ ,lessons 9 ,m9]als0 %\ld be introduc$ "h4 ,m9]alogical ,composition ( ,rocks4 ,! f\rte5 elem5ts nam$ above are comb9$ to =m ab\t fifty m9]als ) :i* ! /ud5t ( geology %\ld be acqua9t$2 b n m ?an "o-half ( ^! are ( ! fir/ importance4 ,x is desir$ to lay especial emphasis ^u ! importance ( a p]fect famili>ity ) ^! few common m9]als4 ,!re is no?+ else 9 ! :ole range ( geology s easily acquir$ :i* is at ! same "t s valuable2 = x is entirely impossible to compreh5d ! def9itions ( rocks1 or to recognize rocks c]ta9ly & sci5tifically1 unless we are acqua9t$ ) _! con/itu5t m9]als4 ,) "o or two exceptions1 ^! common rock-=m+ m9]als may be easily di/+ui%$ by _! physical *>act]s alone1 s t _! c]ta9 recognition is a matt] ( ! simple/ obs]vation1 & entirely )9 ! capacity ( "y *ildr54 ,fur!rmore1 be+ common1 specim5s ( ^! m9]als are v easily obta9$1 s t !re is no reason :y tea*]s %\ld n "h adopt ! be/ me?od & place a specim5 ( ea* m9]al 9 ! h&s ( ea* pupil4 ,typical examples1 l>ge en\gh to %[ ! *>act]i/ics well1 ought n to co/1 on ! av]age1 ov] two c5ts apiece4 ,a ,,m9]al is an inorganic body hav+ !oretically a def9ite *emical composition1 & usually a regul> geometric =m4 ,,! ,,pr9cipal ,,*>act]i/ics ,,( ,,m9]als4--,^! may be gr\p$ "u ! foll[+ g5]al heads3-- 7#a7 ,composition1 7#b7 ,cry/all9e =m1 7#c7 ,h>dness1 7#d7 ,specific gravity1 7#e7 ,lu/re1 7#f7 ,color & ,/reak4 #a4 ,composition4--,?is1 accord+ to ! def9ition ( a m9]al1 ought to be def9ite1 & expressible by a *emical =mula4 ,:5 x is n s1 we usually consid] t ! m9]al is p>tially decompos$1 or t we are deal+ ) a mixture ( m9]als4 ,x is well to impress ^u ! m9d ( ! pupil ! important fact t ! m fundam5tal prop]ties ( ! elem5ts1 su* z specific gravity & lu/re1 are n lo/ :5 !y comb9e1 b may be trac$ 9 ! comp\nds4 ,9 o!r words1 ! prop]ties ( m9]als are1 9 a v l>ge degree1 ! av]age ( ! prop]ties ( ! elem5ts ( :i* !y are compos$2 m9]als 9 :i* heavy metallic elem5ts pr$om9ate be+ heavy & metallic1 & vice v]sa4 ,to fully appreciate ?is po9t x is only necess>y to comp>e a m9]al l gal5ite--a common ore ( lead1 & conta9+ ne>ly #hg p] c5t4 ( t heavy metal2 or hematite 7specim5 #ac71 conta9+ #gj p] c5t4 ( ano!r heavy metal1 iron--) qu>tz 7specim5 #ae71 :i* is compos$ 9 ne>ly equal p>ts ( oxyg5 & silicon1 two typical non-metallic elem5ts4 ,_m m9]als conta9 wat]1 i4e41 are hydrat$4 ,n[ wat]1 :e!r we consid] ! liquid or solid /ate1 is "o ( ! lighte/ & s(te/ ( m9]al con/itu5ts2 & x is a v important fact t hydrat$ m9]als are inv>iably light] & usually s(t] ?an anhydr\s species ( o!rwise simil> composition4 ,o!r /rik+ illu/rations ( ?is pr9ciple w be po9t$ out 9 ! descriptions ( ! m9]als :i* foll[4 #b4 ,cry/all9e =m4--,a cry/al is b\nd$ by plane surfaces symmetrically arrang$ ) ref]5ce to c]ta9 imag9>y l9es pass+ ?r\gh its c5tre & call$ axes4 ,cry/als ( ! same species are always con/ant 9 ! angles betwe5 l planes1 :ile simil> angles usually v>y 9 diff]5t species2 s t ea* species has its own peculi> =m4 8,besides ext]nal symmetry ( =m1 cry/allization produces also regul>ity ( int]nal /ructure1 & (t5 ( fracture4 ,?is regul>ity ( fracture1 or t5d5cy to break or cleave along c]ta9 planes1 is call$ cleavage4 ,! surface af=d$ by cleavage is (t5 smoo? & brilliant 7see specim5s #ag1 #ah1 & #ba71 & is always p>allel ) "s ext]nal plane ( ! cry/al4 ,x %\ld be und]/ood t ! cleavage lamell are n 9 any s5se pres5t be=e !y are made to appe> by fracture40--7,dana47 ,cry/als are arrang$ 9 six sy/ems1 bas$ ^u ! numb] & relations ( ! axes1 z foll[s3-- ,isometric ,sy/em4--,?ree equal axes cross+ at "r angles4 ,example1 cube4 ,tetragonal ,sy/em4--,two axes equal1 ?ird unequal1 all cross+ at "r angles4 ,example1 squ>e prism4 ,or?orhombic ,sy/em4--,?ree unequal axes1 b int]sections all at "r angles4 ,example1 rhombic prism4 ,monocl9ic ,sy/em4--,?ree unequal axes1 "o int]section oblique4 ,example1 oblique rhombic prism4 ,tricl9ic ,sy/em4--,?ree unequal axes1 all cross+ obliquely4 ,example1 oblique rhomboidal prism4 ,hexagonal ,sy/em4--,?ree equal axes ly+ 9 "o plane & int]sect+ at angles ( #fj1 & a f\r? axis cross+ ea* ( ^! at "r angles & long] or %ort]4 ,example1 hexagonal prism4 ,by ! truncation & bevelm5t ( ! angles & edges ( ^! fundam5tal =ms a va/ v>iety ( second>y =ms are produc$4 ,! limits ( ! guide w n p]mit u to foll[ ?is topic f>!r2 b x may be add$ t = ! prop] elucidation ( ev5 ! simpl] cry/all9e =ms ! tea*] %\ld be provid$ ) a set ( wood5 cry/al models & ,dana's 8,text-,book ( ,m9]alogy40 ,! cry/allization ( a m9]al may be manife/$ 9 two ways3 fir/1 by ! regul>ity ( its int]nal /ructure or molecul> arrangem5t1 z %[n by cleavage & ! pol>ization ( transmitt$ light2 &1 second1 by ! regul>ity ( ext]nal =m :i* foll[s1 "u favorable conditions1 z a necess>y consequ5ce ( symmetry 9 ! arrangem5t ( ! molecules4 ,:5 a m9]al is entirely devoid ( cry/all9e /ructure1 bo? ext]nally & int]nally1 x is said to be amorph\s4 ,p]fect & di/9ct cry/als are ! r>e exception1 mo/ m9]al specim5s be+ simply aggregates ( imp]fect cry/als4 ,9 su* cases1 & :5 ! m9]al is amorph\s1 ! /ructure ( ! mass may be3-- ,column> or fibr\s4 ,lamell>1 foliace\s1 or micace\s4 ,granul>4--,:5 ! gra9s or cry/all9e p>ticles are invisible to ! nak$ eye ! m9]al is call$ impalpable1 compact1 or massive4 ,& ! ext]nal =m ( ! mass may be3-- ,botryoidal1 hav+ grape-l surfaces4 ,/alactitic1 =m+ /alactites or p5dant columns4 ,amygdaloidal or ,concretion>y1 =m+ sep>ate globul> masses 9 ! enclos+ rock4 ,d5dritic1 bran*+ or arboresc5t4 #c4 ,h>dness4--,by ! h>dness ( a m9]al we mean ! resi/ance :i* x (f]s to abrasion4 ,b h>dness is a purely relative t]m1 calcite1 = example1 be+ h>d comp>$ ) talc1 b v s(t comp>$ ) qu>tz4 ,h5ce m9]alogi/s h f\nd x necess>y to select c]ta9 m9]als to be us$ z a /&>d ( comp>ison = all o!rs1 & kn[n z ! scale ( h>dness4 ,^! are arrang$ at ne>ly equal int]vals all ! way f ! s(te/ m9]al to ! h>de/1 z foll[s3-- ,scale ( ,h>dness4 7#a7 ,talc4 7#b7 ,gypsum4 7#c7 ,calcite4 7#d7 ,fluorite4 7#e7 ,apatite4 7#f7 ,or?oclase4 7#g7 ,qu>tz4 7#h7 ,topaz or ,b]yl4 7#i7 ,corundum4 7#aj7 ,diamond4 ,if a m9]al scrat*es calcite & is scrat*$ by fluorite1 we say its h>dness is betwe5 #c & #d1 p]haps #c4e2 if x nei!r scrat*es nor is scrat*$ by or?oclase1 its h>dness is #f2 & s on4 ,!re are v few m9]als h>d] ?an qu>tz1 & h5ce ! fir/ sev5 memb]s ( ! scale are suffici5t = all ord9>y purposes2 & ^! are all includ$ 9 ! s]ies ( specim5s accompany+ ?is ,guide4 ,al?\gh x is desirable to be acqua9t$ ) ! scale ( h>dness1 & to und]/& h[ to use x1 /ill ! /ud5t w le>n1 aft] a little practice1 t almo/ z good results may be obta9$ mu* m conv5i5tly by ! use ( 8 ?umb-nail & a good knife-blade or file4 ,talc & gypsum are easily scrat*$ ) ! nail2 calcite & fluorite yield easily to ! knife or file1 apatite ) m difficulty2 :ile or?oclase is ne> ! limit ( ! h>dness ( ord9>y /eel1 & qu>tz is entirely beyond x4 #d4 ,specific ,gravity4--,! specific gravity ( a m9]al1 by :i* we mean its weight z comp>$ ) ! weight ( an equal volume ( wat]1 is det]m9$ by weigh+ x fir/ 9 air & !n 9 wat]1 & divid+ ! weight 9 air by ! diff]5ce ( ! two weights4 ,m9]als exhibit a wide range 9 specific gravity2 f petroleum1 :i* floats on wat]1 to gold1 :i* is ne>ly tw5ty times heavi] ?an wat]4 ,al?\gh ?is is "o ( ! mo/ important prop]ties ( m9]als1 yet1 be+ m difficult to measure ?an h>dness1 x is less valuable z an aid 9 di/+ui%+ species4 ,"o c ) practice1 h[ev]1 e/imate ! d5sity ( a m9]al pretty closely by lift+ x 9 ! h&4 #e4 ,lu/re4--,( all ! prop]ties ( m9]als dep5d+ on _! relations to light ! mo/ important is lu/re1 by :i* we mean ! quality ( ! light reflect$ by a m9]al z det]m9$ by ! "* or m9ute /ructure ( its surface4 ,two k9ds ( lu/re1 ! metallic & vitre\s1 are ( especial importance2 9 fact all o!r k9ds are m]ely v>ieties ( ^!4 ,! metallic lu/re is ! lu/re ( all true metals1 z copp] & t91 & *>act]izes ne>ly all m9]als 9 :i* metallic elem5ts pr$om9ate4 ,! vitre\s lu/re is be/ exemplifi$ 9 glass1 b belongs to mo/ m9]als compos$ *iefly ( non-metallic elem5ts4 ,metallic m9]als are always opaque1 b vitre\s m9]als are (t5 transp>5t4 ,o!r k9ds ( lu/re are ! adamant9e 7! lu/re ( diamond71 res9\s1 pe>ly1 & silky4 ,:5 a m9]al has no lu/re1 l *alk1 x is said to be dull4 ,x %\ld be made cle> to *ildr5 t lu/re & color are entirely di/9ct & indep5d5t4 ,?us1 iron1 copp]1 gold1 silv]1 & lead are all metallic2 :ile :ite or colorless qu>tz1 black t\rmal9e1 gre5 b]yl1 r$ g>net1 etc41 are all vitre\s4 ,g5]ally speak+1 any color may occur ) any lu/re4 #f4 ,color & ,/reak4--,! colors ( m9]als are ( two k9ds1--ess5tial & non-ess5tial4 ,by ! ess5tial color 9 any case we mean ! color ( ! m9]al itself 9 its pure/ /ate4 ,! non-ess5tial colors1 on ! o!r h&1 are *iefly ! colors ( ! impurities conta9$ 9 ! m9]als4 ,metallic m9]als1 :i* are always opaque1 usually h ess5tial colors2 b vitre\s m9]als1 :i* are always m or less transp>5t1 (t5 h non-ess5tial colors4 ,! explanation is ?is3 ,9 opaque m9]als we c only see ! impurities imm$iately on ! surface1 & ^! are1 z a rule1 n en\gh to affect its color2 b 9 diaphan\s m9]als we look into ! specim5 & see impurities bel[ ! surface1 & ?us br+ into view1 9 _m cases1 suffici5t impurity s t its color dr[ns t ( ! m9]al4 ,to prove ?is we h only to take any m9]al 7s]p5t9e is a good example 9 our s]ies7 hav+ a non-ess5tial color1 & make x opaque by pulv]iz+ x or abrad+ its surface1 :5 ! non-ess5tial color1 ! color ( ! impurity1 imm$iately disappe>s2 j z wat]1 yell[ ) susp5d$ clay1 becomes :ite :5 :ipp$ into foam1 & ?us made opaque4 ,:at we und]/& by ! /reak ( a m9]al is its ess5tial color1 ! color ( its p[d]2 & x is s call$ because ! p[d] is mo/ readily obs]v$ by scrat*+ ! surface ( ! m9]al1 & !reby pulv]iz+ a m9ute portion ( x4 ,! /reak & h>dness are ?us det]m9$ at ! same "t4 ,! /reak ( s(t m9]als is easily det]m9$ by rubb+ !m on any :ite surface ( suitable h>dness1 z pap]1 porcela91 or ,arkansas /one4 ,,ess5tial ,,& ,,accessory ,,m9]als4--,li?ologi/s1 reg>d+ m9]als z con/itu5ts ( rocks1 divide !m into two great classes3 ! ess5tial & ! accessory4 ,! ess5tial con/itu5ts ( a rock are ^? m9]als :i* are ess5tial to ! def9ition ( ! rock4 ,= example1 we _c prop]ly def9e granite )\t nam+ qu>tz & or?oclase2 h5ce ^! are ess5tial con/itu5ts ( granite2 & if ei!r ( ^! m9]als 7 remov$ f granite x w\ld n be granite any long]1 b "s o!r rock4 ,b o!r m9]als1 l t\rmal9e & g>net1 may be indiff]5tly pres5t or abs5t2 x is granite /ill2 h5ce !y are m]ely accid5tal or accessory con/itu5ts4 ,!y det]m9e ! diff]5t v>ieties ( granite1 :ile ! ess5tial m9]als make ! species4 ,?is classification1 ( c\rse1 is n absolute1 = 9 _m cases ! same m9]al =ms an ess5tial con/itu5t ( "o rock & an accessory con/itu5t ( ano!r4 ,?us1 qu>tz is ess5tial 9 granite1 b accessory 9 diorite4 ,,pr9cipal ,,m9]als ,,con/itut+ ,,rocks4--,hav+ /udi$ 9 a g5]al way ! m important *>act]i/ics ( m9]als1 brief descriptions ( ! *ief rock-=m+ species are next 9 ord]4 ,we w notice fir/ & pr9cipally ^? m9]als occurr+ *iefly z ess5tial con/itu5ts ( rocks4 #a4 ,graphite4--,ess5tially pure c>bon1 ?\gh (t5 mix$ ) a little iron oxide4 ,cry/allizes 9 hexagonal sy/em1 b usually foliat$1 granul>1 or massive4 ,h>dness1 #a-b1 be+ easily scrat*$ ) ! nail4 ,sp4 gr41 #b4a-b4c4 ,lu/re1 metallic2 an exception to ! rule t acidic elem5ts h non-metallic or vitre\s lu/res4 ,/reak1 black & %9+ 7see p5cil-m>k on :ite pap]74 ,color1 iron-black4 ,slipp]y or greasy feel4 ,e black-lead p5cil is a specim5 ( graphite4 ,specim5 #i4 ,! diff]5t k9ds ( m9]al coal are1 geologically1 z we h se51 closely relat$ to graphite1 b !y are su* famili> sub/ances t !y ne$ n be describ$ "h4 #b4 ,halite 7common salt74--,*loride ( sodium3 *lor9e1 #fj4g2 sodium1 #ci4c2 #ajj4 ,isometric sy/em1 usually =m+ cubes4 ,h>dness1 #b4e1 a little h>d] ?an ! nail4 ,sp4 gr41 #b4a-b4f4 ,lu/re1 vitre\s4 ,/reak & color bo? :ite1 & h5ce color is ess5tial4 ,(t5 transp>5t4 ,soluble2 ta/e1 purely sal9e4 ,9 specific gravity & lu/re x is a good example ( a m9]al 9 :i* an acidic elem5t pr$om9ates4 ,specim5 #aa4 #c4 ,limonite4--,hydr\s sesquioxide ( iron3 oxyg51 #be2 iron1 #fj2 wat]1 #ae2 #ajj4 ,usually amorph\s2 occurr+ 9 /alactitic & botryoidal =ms1 hav+ a fibr\s /ructure2 & also concretion>y1 massive1 & e>?y 7yell[ o*re74 ,h>dness1 #e-e4e4 ,sp4 gr41 #c4f-d4 ,lu/re1 vitre\s or silky1 incl9+ to metallic1 & sometimes dull4 ,color1 v>i\s %ades ( black1 br[n1 & yell[4 ,/reak1 o*re-yell[2 h5ce color p>tly non-ess5tial4 ,specim5 #ab4 #d4 ,hematite4--,sesquioxide ( iron3 oxyg51 #cj2 iron1 #gj2 #ajj4 ,hexagonal sy/em1 9 di/9ct cry/als1 b usually lamell>1 granul>1 or compact1--column>1 botryoidal1 & /alactitic =ms be+ common4 ,h>dness1 #e4e-f4e2 good cry/als are h>d] ?an /eel4 ,sp4 gr41 #d4e-e4c4 ,lu/re1 metallic1 sometimes dull4 ,color1 iron-black1 b r$ :5 e>?y or pulv]iz$ 7r$ o*re74 ,/reak1 r$1 & color1 !re=e1 ma9ly non-ess5tial2 sometimes attract$ by ! magnet4 ,specim5 #ac4 ,hematite has ! same composition z limonite1 m9us ! wat]2 & by comp>+ ! h>dness & specific gravity ( ^! two m9]als we see t !y are a good illu/ration ( ! pr9ciple t hydr\s m9]als are s(t] & light] ?an anhydr\s m9]als ( analog\s composition4 ,limonite & hematite are two great natural color+ ag5ts1 & almo/ all yell[1 br[n1 & r$ colors 9 rocks & soils are due to _! pres5ce4 #e4 ,magnetite4--,protoxide & sesquioxide ( iron3 oxyg51 #bg4f2 iron1 #gb4d2 #ajj4 ,isometric sy/em1 usually 9 octah$rons or dodecah$rons4 ,mo/ abundant v>iety is co>sely to f9ely granul>1 sometimes d5dritic4 ,h>dness1 #e4e-f4e1 same z hematite4 ,sp4 gr41 #d4i-e4b4 ,lu/re1 metallic4 ,color & /reak1 iron-black1 & h5ce color ess5tial4 ,/rongly magnetic2 "s specim5s h di/9ct pol>ity1 & are call$ load/ones4 ,specim5 #ad4 ,! ?ree iron-oxides j describ$--limonite1 hematite1 & magnetite--are all important ores ( iron1 & =m a well-m>k$ natural s]ies4 ,?us limonite is nev]1 hematite is usually1 & magnetite is always1 cry/all9e4 ,aga91 limonite ) #fj p] c5t4 ( iron is nev] magnetic1 hematite ) #gj p] c5t4 is sometimes magnetic1 :ile magnetite ) #gb4d p] c5t4 is always magnetic4 ,z ! iron increases s does ! magnetism4 ,we h "h an excell5t illu/ration ( ! pr9ciple t ! prop]ties ( ! elem5ts c be trac$ 9 ^? m9]als 9 :i* !y pr$om9ate4 ,iron is ! only /rongly magnetic elem5t3 magnetite conta9s m iron ?an any o!r m9]al1 & x is ! only /rongly magnetic m9]al4 ,^! ?ree iron-ores are easily di/+ui%$ f ea* o!r by ! color ( _! p[d]s or /reak1--limonite yell[1 hematite r$1 & magnetite black1--& f all o!r common m9]als by _! high specific gravity4 #f4 ,qu>tz4--,oxide ( silicon or silica3 oxyg51 #ec4cc2 silicon1 #df4fg2 #ajj4 ,hexagonal sy/em4 ,! mo/ common =m is a hexagonal prism t]m9at$ by a hexagonal pyramid4 ,also co>sely & f9ely granul> to p]fectly compact1 l fl9t2 ! compact or cryptocry/all9e v>ieties (t5 assum+ botryoidal1 /alactitic1 & concretion>y =ms4 ,x has no cleavage1 b usually breaks ) an irregul>1 con*oidal fracture l glass4 ,h>dness1 #g1 be+ ,no4 #g ( ! scale2 scrat*es glass easily4 ,sp4 gr41 #b4e-b4h4 ,lu/re1 vitre\s4 ,pure qu>tz is colorless or :ite1 b by admixture ( impurities x may be ( almo/ any color4 ,/reak always :ite or light color$4 ,qu>tz is usually1 z 9 specim5 #ae1 transp>5t & glassy1 b may be transluc5t or opaque4 ,x is almo/ absolutely infusible & insoluble4 ,! v>ieties ( qu>tz are v num]\s1 b !y may be arrang$ 9 two great gr\ps3-- #a4 ,ph5ocry/all9e or vitre\s v>ieties1 includ+ rock-cry/al1 ame?y/1 rose qu>tz1 yell[ qu>tz1 smoky qu>tz1 milky qu>tz1 f]rug9\s qu>tz1 etc4 #b4 ,cryptocry/all9e or compact v>ieties1 includ+ *alc$ony1 c>nelian1 agate1 onyx1 jasp]1 fl9t1 *]t1 etc4 ,only ?ree v>ieties1 h[ev]1 are ( any great geological importance2 ^! are3 common glassy qu>tz 7spec4 #ae71 fl9t 7spec4 #af71 & *]t4 ,qu>tz is "o ( ! mo/ important con/itu5ts ( ! e>?'s cru/1 & x is also ! h>de/ & mo/ durable ( all common m9]als4 ,we h already obs]v$ 7p4 #ab7 t x is entirely unalt]$ by exposure to ! wea!r2 i4e41 x _c be decompos$2 &1 be+ v h>d1 ! same me*anical we> :i*1 assi/$ by m or less *emical decomposition1 r$uces s(t] m9]als to an impalpable p[d] or clay1 mu/ leave ! qu>tz *iefly 9 ! =m ( s& & gravel4 ,?is agrees ) our obs]vation t s& 7spec4 #cj71 especially1 is usually m]ely pulv]iz$ qu>tz4 ,opal is a m9]al closely alli$ to qu>tz1 & may be m5tion$ 9 ?is connection4 ,x is ( simil> composition1 b conta9s f #e to #bj p] c5t4 ( wat]1 & is decid$ly s(t] & light]4 ,h>dness1 #e4e-f4e2 sp4 gr41 #a4i-b4c4 #g4 ,gypsum4--,hydr\s sulphate ( calcium3 sulphur trioxide 7,,s71 #df4e2 lime 7,ca,o71 #cb4f2 wat] 7,h,o71 #bj4i2 #ajj4 ,monocl9ic sy/em4 ,(t5 9 di/9ct rhombic cry/als2 also foliat$1 fibr\s1 & f9ely granul>4 ,h>dness1 #a4e-b2 ! h>de/ v>ieties be+ ,no4 #b ( ! scale ( h>dness4 ,sp4 gr41 #b4c4 ,lu/re1 pe>ly1 vitre\s1 or dull4 ,color & /reak usually :ite or gray4 ,! pr9cipal v>ieties ( gypsum are 7a7 sel5ite1 :i* includes all di/9ctly cry/alliz$ or transp>5t gypsum2 7b7 fibr\s gypsum or sat9-sp>2 7c7 alaba/]1 f9e-gra9$1 light-color$1 & transluc5t4 ,gypsum is easily di/+ui%$ f all common m9]als resembl+ x by its s(tness & ! fact t x is n affect$ by acids4 ,specim5 #ag4 #h4 ,calcite4--,c>bonate ( calcium3 c>bon dioxide 7,,co71 #dd2 lime 7,ca,o71 #ef2 #ajj4 ,hexagonal sy/em1 usually 9 rhomboh$rons1 scal5oh$rons1 or hexagonal prisms4 ,cleavage rhomboh$ral & highly p]fect 7specim5 #ah74 ,also fibr\s & compact to co>sely granul>1 9 /alactitic1 concretion>y1 & o!r =ms4 ,h>dness1 #b4e-c4e1 usually #c 7see scale ( h>dness74 ,sp4 gr41 #b4e-b4ge4 ,lu/re1 vitre\s4 ,color & /reak usually :ite4 ,transp>5t cry/alliz$ calcite is kn[n z ,icel&-sp>1 & is rem>kable = its /rong d\ble refraction4 ,:5 f9ely fibr\s x makes a sat9-sp> simil> to gypsum4 ,geologically speak+1 calcite is a m9]al ( ! fir/ importance1 be+ ! sole ess5tial con/itu5t ( all lime/ones4 ,x is readily di/+ui%$ f alli$ species by its p]fect rhomboh$ral cleavage2 by its s(tness1 be+ easily scrat*$ ) a knife2 & above all by its lively eff]vesc5ce ) acids1 = x is ! only common m9]al eff]vesc+ freely ) cold dilute acid4 ,to apply ?is te/ x is only necess>y to t\* ! specim5 ) a drop ( dilute *lorohydric acid4 ,! eff]vesc5ce1 ( c\rse1 is due to ! escape ( ! c>bon dioxide 9 a gase\s =m4 ,specim5 #ah4 #i4 ,dolomite4--,c>bonate ( calcium & magnesium3 c>bonate ( calcium 7,ca,c,o71 #ed4ce2 c>bonate ( magnesium 7,mg,c,o71 #de4fe2 #ajj4 ,hexagonal sy/em1 be+ ne>ly isomorph\s ) calcite4 ,rhomboh$ral cleavage p]fect4 ,h>dness1 #c4e-d2 sp4 gr41 #b4h-b4i1 be+ h>d] & heavi] ?an calcite4 ,lu/re1 color1 & /reak same z = calcite1 f :i* x is mo/ easily di/+ui%$ by its non-eff]vesc5ce or only feeble eff]vesc5ce ) cold dilute acid1 ?\gh eff]vesc+ freely ) /rong or hot acid4 ,spec4 #ai4 #aj4 ,sid]ite4--,c>bonate ( iron3 c>bon dioxide 7,,co71 #cg4i2 protoxide ( iron 7,fe,o71 #fb4a2 #ajj4 ,cry/allization & cleavage ess5tially ! same z = calcite & dolomite4 ,h>dness1 #c4e-d4e1 & sp4 gr41 #c4g-c4i4 ,lu/re1 vitre\s4 ,color1 :ite1 gray1 & br[n4 ,/reak1 :ite4 ,) acid1 sid]ite behaves l dolomite4 ,x is di/+ui%$ f bo? calcite & dolomite by its high specific gravity1 :i* is easily expla9$ by ! fact t x is l>gely compos$ ( ! heavy elem5t1 iron4 ,) "o exception1 ! fifte5 m9]als :i* we h yet to /udy belong to ! class ( silicates1 :i* includes m ?an "o-f\r? ( ! kn[n species ( m9]als1 &1 omitt+ qu>tz & calcite1 all ( ! really important rock-con/itu5ts4 ,! silicate m9]als may be v conv5i5tly divid$ into two great gr\ps1 ! basic & acidic4 ,?is is n a %>p division2 on ! contr>y1 !re is a p]fectly gradual passage f "o gr\p to ! o!r2 & yet ?is is1 = geological purposes at lea/1 a v natural classification4 ,! divid+ l9e falls 9 ! neighborhood ( #fj p] c5t4 ( silica2 i4e41 all species conta9+ ?is proportion ( silica or less are class$ z basic1 s9ce 9 !m ! basic elem5ts pr$om9ate2 :ile ^? conta9+ m ?an #fj p] c5t4 ( silica are class$ z acidic1 because _! *>act]i/ics are det]m9$ *iefly by ! acid elem5t or silica4 ,! pr9cipal bases occurr+ 9 ! silicates1 nam$ 9 ! ord] ( _! relative importance1 are alum9um1 magnesium1 calcium1 iron1 sodium1 & potassium2 & ( ^!1 magnesium1 calcium1 iron1 & usually sodium1 are especially *>act]i/ic ( basic species4 ,iron is ! heavie/ base2 b all ! bases1 except sodium & potassium1 are heavi] ?an ! acid--silica2 consequ5tly basic m9]als mu/ be1 z a rule1 heavi] ?an acidic m9]als4 ,& s9ce basic m9]als conta9 m iron ?an acidic1 !y mu/ be d>k] color$4 ,9 g5]al1 we say1 d>k1 heavy silicates are basic1 & vice v]sa4 ,all ?is is ( especial importance because 9 ! rocks nature keeps ^! two classes sep>ate 9 a great degree4 #aa4 ,amphibole4--,silicate ( alum9um1 magnesium1 calcium1 iron1 & sodium4 ,! bases occur 9 v v>i\s proportions1 =m+ _m v>ieties2 b ! only v>iety ( especial geological int]e/ is hornbl5de1 ! av]age p]c5tage composition ( :i* is z foll[s3 silica 7,si,o71 #ej2 alum9a 7,al,o71 #aj2 magnesia 7,mg,o71 #ah2 lime 7,ca,o71 #ab2 iron oxide 7,fe,o & ,fe,o71 #h2 & soda 7,na,o71 #b2 #ajj4 ,monocl9ic sy/em3 usually 9 rhombic or six-sid$ prisms :i* may be %ort & ?ick1 b are m (t5 acicul> or blad$4 ,h>dness1 #e-f2 sp4 gr41 #b4i-c4d4 ,lu/re1 vitre\s2 color1 black & gre5i% black2 & /reak simil> to color1 b mu* pal]4 ,comp>e ) qu>tz1 & obs]ve ! /rong contra/ 9 color possible ) m9]als hav+ ! same lu/re4 ,specim5 #bj4 #ab4 ,pyrox5e4--,l amphibole1 ?is species embraces _m v>ieties1 & ^! exhibit a wide range 9 composition2 b ( ^! augite alone is an important rock-con/itu5t4 ,h5ce 9 li?ology we practically sub/itute = amphibole & pyrox5e1 hornbl5de1 & augite respectively4 ,augite is v simil> 9 composition to hornbl5de1 b conta9s usually m lime & less alum9a & alkali4 ,physically1 too1 ^! m9]als are almo/ id5tical1 cry/alliz+ 9 ! same sy/em & 9 v simil> =ms1 & agree+ 9 h>dness1 color1 lu/re1 & /reak4 ,augite is heavi] ?an hornbl5de1 sp4 gr41 #c4b-c4e4 ,a c]ta9 prismatic angle1 :i* 9 augite is #hge1 is #abdcj 9 hornbl5de4 ,sl5d]1 blad$ cry/als are m common ) hornbl5de ?an augite4 ,:5 exam9$ 9 ?9 sections ) ! pol>iz]1 augite does n af=d ! ph5om5on ( di*roism1 :i* is /rongly m>k$ 9 hornbl5de4 ,h[ev]1 z ^! m9]als commonly occur 9 ! rocks1 9 small & imp]fect cry/als1 ^! di/9ctions c only be obs]v$ 9 ?9 sections "u ! microscope2 s t1 z reg>ds ! nak$ eye1 !y are practically indi/+ui%able4 ,x might appe> at fir/ t ! di/9ction ( m9]als s ne>ly id5tical is n an important matt]2 b nature has decre$ o!rwise4 ,augite & hornbl5de are typical examples ( basic m9]als2 b augite is1 bo? 9 its composition & associations1 ! m basic ( ! two4 ,9 pro( ( ?is we ne$ only to "k t x v r>ely occurs 9 ! same rock ) qu>tz1 :ile hornbl5de is f\nd v commonly 9 t association4 ,qu>tz 9 a rock means an excess ( acid or silica1 & almo/ necess>ily implies ! abs5ce ( highly basic m9]als4 ,9 o!r words1 hornbl5de is (t51 & augite v r>ely1 f\nd 9 connection ) acidic m9]als2 & x is ?is diff]5ce ( association *iefly t makes _! di/9ction ess5tial to ! prop] recognition ( rocks2 :ile at ! same "t x af=ds an easy1 ?\gh ( c\rse n absolutely c]ta91 means ( det]m9+ :e!r ! black con/itu5t ( any p>ticul> rock is hornbl5de or augite4 ,mica ,family4--,mica is n ! "n ( a s+le m9]al1 b ( a :ole family ( m9]als1 includ+ "s half-doz5 species4 ,only two1 h[ev]1--muscovite & biotite1--are suffici5tly abundant to engage our att5tion4 ,^! are complex1 basic silicates ( alum9um1 magnesium1 iron1 potassium1 & sodium4 ,! cry/allization ( biotite is hexagonal1 & ( muscovite monocl9ic2 b bo? occur commonly 9 flat six-sid$ =ms4 ,und\bt$ly ! mo/ important & /rik+ *>act]i/ic ( ! :ole mica family is ! rem>kably p]fect cleavage p>allel ) ! basal planes ( ! cry/als1 & ! wond]ful ?9ness1 & above all ! ela/icity1 ( ! cleavage lamell4 ,! cleavage contra/s ! micas ) all o!r common m9]als1 & makes _! c]ta9 id5tification "o ( ! easie/ ?+s 9 li?ology4 ,! micas are s(t m9]als1 ! h>dness rang+ f #b to #c1 & be+ usually easily scrat*$ ) ! nail4 ,sp4 gr4 v>ies f #b4g-c4a4 ,lu/re1 pe>ly2 & /reak1 :ite or uncolor$4 ,! di/+ui%+ features ( muscovite & biotite are z foll[s3-- #ac4 ,muscovite4--,conta9s #dg p] c5t4 ( silica1 #c p] c5t4 ( sesquioxide ( iron1 & #aj p] c5t4 ( alkalies1 *iefly pota%2 & ! *>act]i/ic colors are :ite1 gray1 &1 m r>ely1 br[n & yell[4 ,non-di*roic4 ,usually f\nd 9 association ) acidic m9]als4 ,! mica us$ 9 ! arts is muscovite4 ,specim5 #ba4 #ad4 ,biotite4--,conta9s only #cf p] c5t4 ( silica1 #bj p] c5t4 ( oxide ( iron1 & #ag p] c5t4 ( magnesia2 colors1 deep black to gre54 ,/rongly di*roic4 ,commonly occurs ) o!r basic m9]als4 ,comp>e color ) p] c5t4 ( iron4 ,^! diff]5ces are tabulat$ bel[3-- ,muscovite ,biotite ,acidic mica4 ,basic mica4 ,non-f]rug9\s mica4 ,f]rug9\s mica4 ,pota% mica4 ,magnesian mica4 ,:ite mica4 ,black mica4 ,non-di*roic mica4 ,di*roic mica4 ,feldsp> ,family4--,l mica1 feldsp> is ! "n ( a family ( m9]als2 & ^! are1 geologically1 ! mo/ important ( all m9]als4 ,!y are1 above all o!rs1 ! m9]als ( :i* rocks are made1 & _! abundance is well express$ 9 ! "n1--feldsp> be+ simply ! ,g]man = field-sp>1 imply+ t x is ! common sp> or m9]al ( ! fields4 ,*emically1 ! feldsp>s are silicates ( alum9um & potassium1 sodium or calcium4 ,!y cry/allize 9 ! monocl9ic & tricl9ic sy/ems2 & all possess easy cleavage 9 two directions at "r angles to ea* o!r1 or ne>ly s4 ,! g5]al physical *>act]s1 includ+ ! cleavage1 are well exhibit$ 9 ! common species1 or?oclase 7specim5 #bb74 ,9 h>dness ! feldsp>s range f #e to #g1 be+ usually ne> #f1 & almo/ always di/9ctly s(t] ?an qu>tz4 ,sp4 gr4 v>ies f #b4e-b4ge2 lu/re1 f vitre\s to pe>ly2 color1 f :ite & gray to r$1 br[n1 gre51 etc41 b usually light4 ,/reak1 always :ite2 r>ely transp>5t4 ,by exposure to ! wea!r1 feldsp>s gradually lose _! alkalies & lime1 become hydrat$1 & are *ang$ to kaol9 or common clay4 ,a simil> *ange takes place ) ! micas1 augite1 & hornbl5de2 b ^! species1 be+ usually ri* 9 iron1 make clays :i* are mu* d>k] color$ ?an ^? d]iv$ f feldsp>s4 ,! fact t ! feldsp>s conta9 little or no iron und\bt$ly expla9s _! l[ specific gravity & light colors1 z comp>$ ) ! o!r m9]als j nam$4 ,! only common m9]als = :i* ! feldsp>s are liable to be mi/ak5 are qu>tz & ! c>bonates4 ,f ! latt] !y are easily di/+ui%$ by _! sup]ior h>dness & non-eff]vesc5ce ) acids2 & f ! =m]1 by possess+ di/9ct cleavage1 by be+ r>ely transp>5t1 by be+ some:at s(t]1 & by *ang+ to clay on exposure to ! wea!r4 ,! feldsp>s ( greate/ geological int]e/ are five 9 numb]1 & may be classifi$ *emically z foll[s3-- ,or?oclase1--silicate ( alum9um & potassium1 or pota% feldsp>4 ,albite1--silicate ( alum9um & sodium1 or soda feldsp>4 ,anor?ite1--silicate ( alum9um & calcium1 or lime feldsp>4 ,oligoclase1--silicate ( alum9um & sodium1 & calcium1 or soda-lime feldsp>4 ,labradorite1--silicate ( alum9um & calcium1 & sodium1 or lime-soda feldsp>4 ,?is appe>s l a complex arrangem5t1 b x c be simplifi$4 ,or?oclase cry/allizes 9 ! monocl9ic sy/em1 & all ! o!r feldsp>s 9 ! tricl9ic sy/em4 ,) ! exception ( albite1 :i* is a comp>atively r>e species1 ! tricl9ic feldsp>s all conta9 less silica ?an or?oclase2 i4e41 are m basic4 ,?is is %[n by ! subjo9$ table giv+ ! av]age composition ( ea* ( ! feldsp>s3-- ,si,o ,al,o ,k,o ,na,o ,ca,o ,total4 ,or?oclase1 #fe #ah #ag -- -- #ajj ,albite1 #fh #bj -- #ab -- #ajj ,oligoclase1 #fb #bd -- #i #e #ajj ,labradorite1 #ec #cj -- #d #ac #ajj ,anor?ite1 #dc #cg -- -- #bj #ajj ,z we %\ld naturally expect1 ! tricl9ic feldsp>s occur usually ) o!r basic m9]als1 :ile ! monocl9ic species1 or?oclase1 is acidic 9 its associations2 fur!rmore1 ! tricl9ic feldsp>s are (t5 intimately associat$ ) ea* o!r1 b are r>ely important con/itu5ts ( rocks conta9+ mu* or?oclase4 ,9 o!r words1 ! di/9ction ( or?oclase f ! basic or tricl9ic feldsp>s is important & comp>atively easy1 :ile ! di/9ction ( ! diff]5t basic feldsp>s f ea* o!r is bo? unimportant & difficult4 ,h5ce1 9 li?ology1 we f9d x be/ to put all ^! basic feldsp>s toge!r1 z if !y 7 "o species1 "u ! "n plagioclase1 :i* ref]s to ! oblique cleavage ( all ^! feldsp>s1 & contra/s ) or?oclase1 :i* ref]s to ! "r-angl$ cleavage ( t species4 ,?is /atem5t ( ! relations ( ! feldsp>s is1 ( c\rse1 beyond ! compreh5sion ( _m *ildr51 & yet x %\ld be und]/ood by ! tea*] :o w\ld lead ! *ildr5 to any b ! mo/ sup]ficial views4 #ae4 ,or?oclase4--,?is is ! common feldsp>1 & ! mo/ abundant ( all m9]als1 be+ ! pr9cipal con/itu5t ( granite1 gneiss1 & _m o!r important rocks4 ,! mo/ *>act]i/ic colors are :ite1 gray1 p9ki%1 & fle%-r$4 ,specim5 #bb4 #af4 ,plagioclase4--,l or?oclase1 ^! species may be ( almo/ any color2 yet ^! two great divisions ( ! feldsp>s are usually contra/$ 9 ?is respect4 ,?us1 blui% & grayi% colors are mo/ common ) plagioclase1 & :ite or r$di% colors ) or?oclase4 ,specim5 #bc is labradorite1 &1 9 e respect1 a typical example ( plagioclase4 ,on c]ta9 faces & cleavage-surfaces ( ! plagioclase cry/als we may (t5 obs]ve a s]ies ( /raight p>allel l9es or b&s :i* are (t5 v f9e1--fifty to a hundr$ 9 a s+le cry/al4 ,^! /ri are due to ! mode ( tw9n+1 & are ( especial importance1 s9ce1 :ile !y are v *>act]i/ic ( plagioclase1 !y nev] occur 9 or?oclase4 ,z /at$1 ^! tw9n+ /ri 9 plagioclase are (t5 visible to ! nak$ eye2 & :5 !y are n1 !y may usually be reveal$ by exam9+ a ?9 section "u ! microscope ) pol>iz$ light4 ,plagioclase decays mu* m rapidly :5 expos$ to ! wea!r ?an or?oclase4 ,?is po9t becomes p]fectly cle> :5 we comp>e wea!r$ l$ges ( diabase 7or any trap-rock1 see specim5 #b7 & granite2 = plagioclase is ! pr9cipal con/itu5t ( ! =m] rock1 & or?oclase ( ! latt]4 ,hydr\s ,silicates4--,_m silicates conta9 wat]1 & "s ( ^! are ( great geological importance4 ,:at has be5 /at$ on a prec$+ page conc]n+ ! s(tness & lightness ( hydrat$ m9]als is especially applicable "h2 = all ! geologically important hydr\s silicates are di/9ctly s(t] & light] ?an anhydr\s m9]als ( o!rwise simil> composition4 ,fur!rmore1 !y usually h an unctu\s or slipp]y feel2 &1 ) "o exception 7kaol971 are ( a gre5 or gre5i% color4 #ag4 ,kaol9ite 7,kaol974--,hydr\s silicate ( alum9um3 silica 7,si,o71 #df2 alum9a 7,al,o71 #dj2 & wat] 7,h,o71 #ad2 #ajj4 ,or?orhombic sy/em1 9 rhombic or hexagonal scales or plates1 b usually e>?y or clay-l4 ,h>dness1 #a-b4e2 sp4 gr41 #b4d-b4fe4 ,! pure m9]al is :ite2 b x is usually color$ by impurities1 ! pr9cipal ( :i* are iron oxides & c>bonace\s matt]4 ,kaol9 is ! mo/ abundant ( all ! hydr\s silicates1 & x is ! basis & (t5 ! sole con/itu5t ( common clay1--a v common m9]al1 b r>ely pure4 ,we h already 7p4 #aa7 notic$ ! mode ( orig9 ( kaol9 or clay4 ,x results f ! decomposition ( v>i\s alum9\s silicate m9]als1 especially ! feldsp>s4 ,"u ! comb9$ influ5ce ( c>bon dioxide & moi/ure1 feldsp>s give up _! potassium1 sodium1 & calcium1 & take on wat]1 & ! result is kaol94 ,?is m9]al is believ$ to be always a decomposition product4 ,p]haps ! be/1 or at lea/ ! mo/ conv5i5t1 te/ = kaol9 is ! argillace\s odor1 ! odor ( moi/5$ clay4 ,specim5 #bd4 #ah4 ,talc4--,hydr\s silicate ( magnesium3 silica 7,si,o71 #fc 7acidic72 magnesia 7,mg,o71 #cb2 wat] 7,h,o71 #e2 #ajj4 ,or?orhombic sy/em1 b r>ely 9 di/9ct cry/als4 ,cleavage 9 "o direction v p]fect2 ! cleavage lamell are flexible1 b n ela/ic1 z 9 mica4 ,h>dness1 #a2 see scale4 ,sp4 gr41 #b4ee-b4h4 ,lu/re1 pe>ly4 ,color1 apple-gre5 to :ite2 & /reak1 :ite4 ,! feel is v smoo? & greasy2 &1 9 connection ) ! color & foliation1 af=ds ! be/ means ( di/+ui%+ talc f alli$ m9]als4 ,talc sometimes results f ! alt]ation ( augite1 hornbl5de1 & o!r m9]als1 b x is n always nor usually an alt]ation product4 #ai4 ,s]p5t9e4--,hydr\s silicate ( magnesium3 silica 7,si,o71 #dd 7basic72 magnesia 7,mg,o71 #dd2 wat] 7,h,o71 #ab2 #ajj4 ,ess5tially amorph\s4 ,h>dness1 #b4e-d2 sp4 gr41 #b4e-b4fe4 ,lu/re1 greasy1 waxy1 or e>?y4 ,color1 v>i\s %ades ( gre5 & usually d>k] ?an talc1 b /reak always :ite4 ,feel1 smoo?1 sometimes greasy4 ,di/+ui%$ f talc by its h>dness1 compactness1 & d>k] gre54 ,sometimes results f ! alt]ation ( oliv9e & o!r magnesian m9]als1 b usually we are to reg>d x z an orig9al m9]al4 ,specim5 #be4 #bj4 ,*lorite4--,?is is1 prop]ly1 ! "n ( a gr\p ( highly basic m9]als ( v v>iable composition1 b !y are all ess5tially hydr\s silicates ( alum9um1 magnesium1 & iron2 & ! av]age composition ( ! mo/ abundant species1 pro*lorite1 is z foll[s3 silica 7,si,o71 #cj2 alum9a 7,al,o71 #ah2 magnesia 7,mg,o71 #ae2 protoxide ( iron 7,fe,o71 #bf2 & wat] 7,h,o71 #aa2 #ajj4 ,! *lorites cry/allize 9 sev]al diff]5t sy/ems1 b 9 all !re is a highly p]fect cleavage 9 "o direction1 giv+1 z 9 talc1 a foliat$ /ructure ) flexible b inela/ic lam94 ,! cleavage scales1 h[ev]1 are sometimes m9ute1 & ! /ructure massive or granul>4 ,h>dness ( pro*lorite1 #a-b2 betwe5 talc & s]p5t9e4 ,sp4 gr41 #b4gh-b4if4 ,all ! *lorites h a pe>ly to vitre\s lu/re4 ,color usually "s %ade ( gre52 9 pro*lorite a d>k or blacki% gre51 d>k] ?an s]p5t9e1 z t is d>k] ?an talc4 ,/reak1 a light]1 :iti% gre54 ,less unctu\s ?an talc1 b m s ?an s]p5t9e4 ,! *lorites are produc$ v commonly1 b n g5]ally1 by ! alt]ation ( basic anhydr\s silicates1 l augite & hornbl5de4 ,specim5 #bf4 #ba4 ,hydro-mica4--,?is1 too1 is prop]ly ! "n ( a gr\p ( m9]als2 b = geological purposes !y may be reg>d$ z "o species4 ,tak+ a g5]al view ( ! composition1 ^! are simply ! anhydr\s or ord9>y micas1 :i* we h already /udi$1 ) f #e to #aj p] c5t4 ( wat] add$4 ,9 cry/allization & /ructure !y are ess5tially mica-l4 ,al?\gh n di/9ctly s(t] ?an ! common micas1 !y are light]1 always m unctu\s & slipp]y1 & usually ( a gre5i% color4 ,! micace\s /ructure ) ela/ic lam9 s]ves to di/+ui% ! hydro-micas f o!r hydr\s silicates4 #bb4 ,glauconite4--,hydr\s silicate ( alum9um1 iron1 & potassium3 silica 7,si,o71 #ej2 alum9a 7,al,o71 protoxide ( iron 7,fe,o71 & pota% 7,k,o71 toge!r1 #da2 & wat] 7,h,o71 #i2 #ajj4 ,amorph\s1 =m+ r\nd$ & g5]ally loose gra9s1 :i* (t5 h a microscopic organic nucleus4 ,x is dull & e>?y1 l *alk1 & always s(t1 gre51 & light1 b n p>ticul>ly unctu\s4 ,glauconite is ! pr9cipal1 (t5 ! sole1 con/itu5t ( ! rock gre5s&1 :i* occurs abundantly 9 ! new] geological =mations1 & is n[ =m+ 9 ! deep wat] ( ! ,gulf ( ,mexico & along our ,atlantic sea-bo>d4 ,specim5 #bg4 ,?is completes our li/ ( m9]als occurr+ *iefly z ess5tial con/itu5ts ( rocks2 & foll[+ are ?ree ( ! m common & important m9]als occurr+ *iefly z accessory1 r>ely z ess5tial1 rock-con/itu5ts4 #bc4 ,*rysolite 7,oliv9e74--,silicate ( magnesium & iron3 silica 7,si,o71 #da2 magnesia 7,mg,o71 #ea2 protoxide ( iron 7,fe,o71 #h2 #ajj4 ,or?orhombic sy/em2 b usually 9 irregul> glassy gra9s4 ,h>dness1 #f-g4 ,sp4 gr41 #c4c-c4e4 ,lu/re1 vitre\s2 color1 usually "s %ade ( gre52 & /reak1 :ite4 ,*rysolite sometimes closely resembles qu>tz1 b its gre5 color usually suffices to di/+ui% x4 ,x is a common con/itu5t ( basalt & alli$ rocks4 ,by absorption ( wat] x is *ang$ into s]p5t9e & talc4 ,see examples 9 specim54 #bd4 ,g>net4--,! composition ( ?is m9]al is extremely v>iable2 b ! mo/ important v>iety is a basic silicate ( alum9um & iron3 silica 7,si,o71 #cg2 alum9a 7,al,o71 #bj2 & protoxide ( iron 7,fe,o71 #dc2 #ajj4 ,isometric sy/em1 usually 9 di/9ct cry/als1 twelve-sid$ 7dodecah$rons7 & tw5ty-f\r-sid$ 7trapezoh$rons7 =ms be+ mo/ common4 ,h>dness1 #f4e-g4e2 av]age z h>d z qu>tz4 ,sp4 gr41 #c4ae-d4c2 comp>e ) ! high p]c5tage ( iron4 ,lu/re1 vitre\s2 colors1 v>i\s1 usually "s %ade ( r$ or br[n2 & /reak1 :ite4 ,"s v>ieties conta9 iron en\gh to make !m magnetic4 ,g>net is easily di/+ui%$ by its =m1 color1 & h>dness f all o!r m9]als4 ,x is a common b n an abundant m9]al1 occurr+ mo/ frequ5tly 9 gneiss1 mica s*i/1 & o!r /ratifi$ cry/all9e rocks4 ,see examples 9 specim54 #be4 ,pyrite4--,sulphide ( iron3 sulphur1 #ec4c2 iron1 #df4g2 #ajj4 ,isometric sy/em1 occurr+ usually 9 di/9ct cry/als1 ! cube & ! twelve-sid$ =m kn[n z ! pyritoh$ron be+ ! mo/ common4 ,h>dness1 #f-f4e1 /rik+ fire ) /eel4 ,sp4 gr41 #d4h-e4b2 heavy because ri* 9 iron4 ,lu/re1 metallic & spl5d5t4 ,color1 pale1 brass-yell[1 & /reak1 gre5i% or br[ni%4 ,pyrite is sometimes mi/ak5 = gold1 b x is n malleable2 :ile its color1 h>dness1 & specific gravity1 comb9$1 easily di/+ui% x f all common m9]als4 ,z an accessory rock-con/itu5t1 pyrite occurs usually 9 isolat$ cubes or pyritoh$rons4 ,specim5 #aj4 ,textures ( ,rocks4 ,texture is a g5]al "n = ^? small] /ructural features ( rocks :i* c be /udi$ 9 h& specim5s1 & :i* dep5d ^u ! =ms & sizes ( ! con/itu5t p>ticles ( ! rocks1 & ! ways 9 :i* ^! are unit$4 ,by 8con/itu5t p>ticles0 we mean1 n ! atoms or molecules ( matt] compos+ ! rocks1 b ! pebbles 9 conglom]ate1 gra9s ( s& 9 s&/one1 cry/als ( qu>tz1 feldsp>1 & mica 9 granite1 etc4 ,! f\r mo/ important textures are3-- 7#a7 ,fragm5tal texture4--,! rock is compos$ ( m]e irregul>1 angul>1 or r\nd$1 b visible1 fragm5ts4 ,examples3 s&1 s&/one1 gravel1 conglom]ate1 etc4 ,specim5s #cj1 #ca1 #bh1 #bi4 7#b7 ,cry/all9e texture4--,! con/itu5t p>ticles are *iefly1 at lea/1 di/9ctly cry/all9e1 z %[n ei!r by ext]nal =m1 or cleavage1 or bo?4 ,examples3 granite1 diabase1 gneiss1 etc4 ,specim5s #de1 #a1 #da4 7#c7 ,compact texture4--,! con/itu5t p>ticles are indi/+ui%able by ! nak$ eye1 b become visible "u ! microscope1 appe>+ z sep>ate cry/all9e gra9s or z irregul> fragm5ts4 ,9 o!r words1 if1 9 ! case ( ei!r ! granul> or cry/all9e textures1 we conceive ! p>ticles to become microscopically small1 !n we h ! compact texture4 ,examples3 clay1 slate1 _m lime/ones1 basalt1 etc4 ,specim5s #cd1 #ce1 #ci4 7#d7 ,vitre\s texture4--,! texture ( glass1 9 :i* ! con/itu5t p>ticles are absolutely invisible ev5 ) ! highe/ p[]s ( ! microscope1 & may be no?+ m ?an ! molecules ( ! sub/ance1 :i* ?us1 s f> z our p[]s ( obs]vation are conc]n$1 pres5ts a p]fectly cont9u\s surface4 ,examples3 obsidian1 glassy qu>tz1 & "s k9ds ( coal4 ,specim5s #dg1 #ae4 ,^! f\r textures1 :i*1 x w be obs]v$1 are det]m9$ by ! =ms & sizes ( ! con/itu5t p>ticles1 may be call$ ! prim>y textures1 because e rock mu/ possess "o ( !m4 ,we _c conceive ( a rock :i* is nei!r fragm5tal1 cry/all9e1 compact1 nor vitre\s4 ,b 9 addition to "o ( ! prim>y textures1 a rock may or may n h "o or m ( :at may be call$ second>y textures4 ,^! are det]m9$ by ! way 9 :i* ! p>ticles are unit$1 ! mode or patt]n ( ! arrangem5t1 etc4 ,foll[+ are def9itions ( ! pr9cipal second>y textures3-- 7#a7 ,lam9at$ texture4--,?is exi/s :]e ! p>ticles are arrang$ 9 ?91 p>allel lay]s1 :i* may be m>k$ simply by planes ( division1 or ! alt]nate lay]s may be compos$ ( p>ticles diff]+ 9 composition1 =m1 size1 or color1 etc4 ,among ! lam9at$ textures we ?us di/+ui%3 7a7 ! b&$ texture1 :]e ! lay]s are contra/$ 9 color1 texture1 or composition1 b coh]e1 s t !re is no cleavage or easy splitt+ p>allel ) ! /ratification2 & 7b7 ! s*i/ose or %aly texture1 :]e su* fissility or /ratification-cleavage exi/s4 ,if a fragm5tal1 compact1 or vitre\s rock is fissile1 we use ! t]m %aly2 b a fissile1 cry/all9e rock is describ$ z s*i/ose4 ,! b&$ texture may occur ) ! fragm5tal1--b&$ s&/ones1 etc42 ) ! cry/all9e1--_m gneisses1 etc4 7specim5 #da72 ) ! compact1--_m slates1 lime/ones1 felsites1 etc4 7specim5s #cd1 #db72 ) ! vitre\s1--b&$ obsidian1 furnace slags1 & "s coal4 ,! s*i/ose texture may occur ) ! cry/all9e1--mica s*i/1 etc4 7specim5 #dc72 & ! %aly texture ) ! compact & fragm5tal1 b r>ely ) ! vitre\s4 7#b7 ,porphyritic texture4--,we h ?is texture :5 sep>ate & di/9ct cry/als ( any m9]al1 b mo/ commonly ( feldsp>1 are enclos$ 9 a relatively f9e-gra9$ base or matrix1 :i* may be ei!r cry/all9e1 compact1 or vitre\s1 b r>ely fragm5tal4 ,specim5s #e1 #f1 #g are examples ( ! porphyritic compact texture4 7#c7 ,concretion>y texture4--,:5 "o or m con/itu5ts ( a rock h ! =m1 9 :ole or 9 "p1 n ( di/9ct angul> cry/als1 b ( r\nd$ concretions1 ! texture is describ$ z concretion>y1 ! concretions tak+ ! place 9 ?is texture ( ! isolat$ cry/als 9 ! porphyritic texture4 ,?is texture occurs 9 connection ) all ! prim>y textures1 b ! mo/ famili> example is olitic lime/one4 7#d7 ,vesicul> texture4--,a rock has ?is texture :5 x conta9s num]\s small cavities or vesicles4 ,^! are mo/ commonly produc$ by ! expansion ( /eam & o!r vapors :5 ! rock is 9 a pla/ic /ate2 & h5ce ! vesicul> texture is f\nd *iefly 9 volcanic rocks4 ,except r>ely1 x is associat$ only ) ! compact texture1--ord9>y /ony lavas 7specim5 #di72 & ) ! vitre\s texture1--pumice 7specim5 #dh74 7#e7 ,amygdaloidal texture4--,9 ! c\rse ( "t ! vesicles ( common lava are (t5 fill$ ) v>i\s m9]als deposit$ by infiltrat+ wat]s1 giv+ rise to ! amygdaloidal texture1 f ! ,lat9 amygdalum1 an almond1 9 allusion to a common =m ( ! vesicles1 or amygdules1 z !y are call$1 aft] be+ fill$4 ,! amygdaloidal texture is ?us necess>ily prec$$ by ! vesicul>1 & is limit$ to ! same classes ( rocks4 ,specim5 #ej4 ,besides ! =ego+1 !re are _m m9or second>y textures4 ,! rocks kn[n z tufas h :at may be call$ ! tuface\s texture4 ,!n we h k9ds ( texture dep5d+ on ! /r5g? ( ! union ( ! p>ticles1 z /rong1 weak1 friable1 e>?y1 etc4 ,classification ( ,rocks4 ,hav+ f9i%$ our prelim9>y obs]vations on ! *>act]i/ics ( rocks1 we are n[ ab\t ready to beg9 a sy/ematic /udy ( ! rocks !mselves2 b x is ne$ful fir/ to say a few words ab\t ! classification ( rocks1 s9ce ^u ?is dep5ds n only ! ord] 9 :i* we %all take ! rocks up1 b also ! ideas t w be imp>t$ conc]n+ _! relations & aff9ities4 ,! classifications :i* h be5 propos$ at diff]5t times are almo/ z num]\s z ! rocks !mselves4 ,"s ( ^! are confess$ly1 & ev5 design$ly1 artificial1 z :5 we classify /ones accord+ to _! uses 9 ! arts1 etc4 ,b we want some?+ m sci5tific1 a natural classification2 t is1 "o bas$ ^u ! natural & p]man5t *>act]i/ics ( rocks4 ,rocks h be5 classifi$ accord+ to *emical composition1 m9]alogical composition1 texture1 color1 d5sity1 h>dness1 etc42 b ^! arrangem5ts1 tak5 s+ly or all comb9$1 are inadequate4 ,a natural classification may be def9$ z a concise & sy/ematic /atem5t ( ! natural relations exi/+ among ! objects classifi$4 ,n[ ! mo/ important relations exi/+ among rocks are ^? due to _! diff]5t orig9s4 ,we mu/ n =get t li?ology is a bran* ( geology1 & t geology is fir/ ( all a dynamical sci5ce4 ,! mo/ important "q t c be ask$ ab\t any rock is1 n ,:at is x made (8 b ,h[ 0 x made8 ,:at 7 ! g5]al =ces or ag5cies conc]n$ 9 its =mation8 ,rocks are ! mat]ial 9 :i* ! e>?'s hi/ory is writt51 & :at we want to "k fir/ conc]n+ any rock is :at x c tell u ( ! condition ( t "p ( ! e>? at ! "t x 0 made & subsequ5tly4 ,classification ( ,rocks4 ---------------------------------------- ---------------------------------- ,s$im5t>y or ,/ratifi$ ,rocks4 ---------------------------------------- ---------------------------------- ,,me*anically ,,=m$4 ---------------------------------------- -------------------------------- ,unconsolidat$4 ,consolidat$4 ---------------------------------------- -------------------------------- ,conglom]ate ,gravel4 ,conglom]ate4 gr\p4 ---------------------------------------- -------------------------------- ,ar5ace\s ,s&4 ,s&/one4 gr\p4 ---------------------------------------- -------------------------------- ,argillace\s ,clay4 ,slate4 gr\p4 ---------------------------------------- -------------------------------- ,,*emically ,,& ,,organically ,,=m$4 ---------------------------------------- -------------------------------- ,coal ,iron-ore ,calc>e\s ,metamorphic gr\p 7,silicates74 gr\p4 gr\p4 gr\p4 ,acidic4 ,basic4 _/----_/---- _/-------_/------- #he #hj #gj #fj #ej #dj #cj ---------------------------------------- ------------------------------- ,feldspa?ic4 ---------------------------------------- ------------------------------- ,peat4 ,limonite4 ,lime/one4 ,gneiss4 ,diorite4 3 ,lignite4 ,hematite4 ,dolomite4 444444444444444444444444444 3 ,bit4 ,coal4 ,magnetite4 ,gypsum4 3 3 3 3 3 ,an?racite4 ,sid]ite4 ,rock-salt4 3 3,sy5ite4 ,norite4 3 ,graphite4 ,phosphate 3 3 44444444444444 3 ,asphaltum4 ,rock4 3 3 3 3 3 ---------------------------------------- ------------------------------- ,non-,feldspa?ic4 ---------------------------------------- ------------------------------- ,silice\s 3 ,mica ,s*i/4 3 3 gr\p4 444444444444444444444444444 3 ----------- 3 3 3 3 3 ,tripolite4 3,hornbl4 ,s*i/4 ,amphibolite4 ,fl9t4 344444444444444 444444443 ,silice\s 3 3 3 3 3 ,tufa4 3 ,talc ,s*i/4 3,*l4 ,s*i/4 ,novaculite4 3 344444444 3 4444444444 3 3 3 3 3 3 3 ,gre5s&4 ,s]p5t9e4 3 3 44444444444 44444444 3 3 3 3 3 ---------------------------------------- ------------------------------- ,eruptive or ,un/ratifi$ ,rocks4 ---------------------------------------- --------------------------------- ,,plutonic4 ,feldspa?ic4 ------------------------------------- 3 ,granite4 3 ,diorite4 3 444444444444444444 44444444 3 3 3 3 3 3 3 3 ,sy5ite4 ,diabase4 3 3 4444444 44444443 3 3 3 3 3 ------------------------------------- ,,volcanic4 ,?is "p ( ! classification ,feldspa?ic4 is a blank1 = ! reason t ------------------------------------- no eruptive rocks are kn[n 3,rhyolite4 3 ,&esite4 3 :i* are *iefly compos$ ( 444444444444444444444444444 3 m9]als belong+ to ! classes 3 3 3 3 3 ( ,native ,elem5ts1 ,*lorides1 3 3 ,tra*yte4 ,basalt4 ,oxides1 ,sulphates1 or ,c>bonates2 4444444444444443 i4e41 all eruptive rocks1 s 3 3 3 3 3 f> z kn[n1 are pr9cipally 3,obsidian4 3 ,ta*ylite43 compos$ ( m9]als belong+ 4444444444444444444444444444 3 to ! class ( ,silicates4 3 3 3 3 3 ,petrosilex4 3,porphyrite43 4444444444444444444444444444 3 3 3 3 3 3 3 3 ,felsite4 ,melaphyr4 3 3 4444444 44444443 3 3 3 3 3 ---------------------------------------- --------------------------------- ,! geological ag5cies1 z we h already le>n$1 may be arrang$ 9 two great classes3 fir/1 ! aque\s or sup]ficial ag5cies orig9at+ 9 ! sol> heat1 & produc+ ! s$im5t>y or /ratifi$ rocks2 &1 second1 ! igne\s or subt]ranean ag5cies orig9at+ 9 ! c5tral or int]ior heat1 & produc+ ! eruptive or un/ratifi$ rocks4 ,h5ce1 we want to "k fir/ ( any rock :e!r x is ( aque\s or igne\s orig94 ,!n1 if x is a s$im5t>y rock1 :e!r x has be5 =m$ by ! action *iefly ( me*anical =ces1 or ( *emical & organic =ces4 ,&1 if x is an eruptive rock1 :e!r x has cool$ & solidifi$ bel[ ! e>?'s surface 9 a fissure1 & is a dike or trappean rock1 or has fl[$ out on ! surface & cool$ 9 contact ) ! air1 & ?us become an ord9>y lava or volcanic rock4 ,"h we h ! outl9es ( our classification1 & x w be obs]v$ t we h simply rea*$ ! conclusion1 9 a some:at r\ndab\t mann]1 t !re %\ld always be a g5]al correspond5ce betwe5 ! classification ( rocks & ! classification ( ! =ces t produce !m4 ,! g5]al plan ( ! prec$+ s*eme ( ! classification mu/ n[ be cle>1 & ! details w be expla9$ z we g along4 ,descriptions ( ,rocks4 #a4--,s$im5t>y or ,/ratifi$ ,rocks4 #a4 ,,me*anically ,,=m$ ,,or ,,fragm5tal ,,rocks4--,^! consi/ ( mat]ials deposit$ f susp5sion 9 wat]1 & ! process ( _! =mation is ?r\gh\t *iefly me*anical4 ,! mat]ials deposit$ are m]e fragm5ts ( old] rocks2 &1 if ! fragm5ts are l>ge1 we call ! newly deposit$ s$im5t gravel2 if f9]1 s&2 &1 if impalpably f9e1 clay4 ,^! fragm5tal rocks _c be classifi$ *emically1 s9ce ! same h&ful ( gravel1 = in/ance1 may conta9 pebbles ( _m diff]5t k9ds ( rocks1 & ?us be ( almo/ any & v v>iable composition4 ,su* *emical di/9ctions z c be e/abli%$ are only p>tial1 & ! classification1 l ! orig91 mu/ be me*anical4 ,accord+ly1 z j %[n1 we recognize ?ree pr9cipal gr\ps bas$ ^u ! size ( ! fragm5ts2 viz43-- 7#a7 ,conglom]ate gr\p4 7#b7 ,ar5ace\s gr\p4 7#c7 ,argillace\s gr\p4 ,?is mode ( division is possible & natural1 simply because1 z we obs]v$ 9 an e>ly exp]im5t1 mat]ials arrang$ by ! me*anical action ( wat] are always assort$ accord+ to size4 ,:5 fir/ deposit$1 ! gravel1 s&1 & clay are1 ( c\rse1 p]fectly loose & unconsolidat$2 b 9 ! c\rse ( "t !y may1 "u ! influ5ce ( pressure1 heat1 & *emical action1 atta9 almo/ any degree ( consolidation1 becom+ conglom]ate1 s&/one1 & slate1 respectively4 ,! pressure may be v]tical :]e x is due to ! weight ( new] deposits1 or horizontal :]e x results f ! cool+ & %r9k+ ( ! e>?'s int]ior4 ,! heat may result f me*anical movem5ts1 or contact ) eruptive rocks2 or x may be due simply to ! burial ( ! s$im5ts1 :i*1 x w be se51 mu/ virtually br+ !m ne>] ! great s\rce ( heat 9 ! e>?'s int]ior1 on ! same pr9ciple t ! temp]ature ( a man's coat1 on a cold day1 is rais$ by putt+ on an ov]coat4 ,! effect ( ! heat1 ord9>ily1 is simply dry+1 cop]at+ ) ! pressure to expel ! wat] f ! s$im5ts2 b1 if ! temp]ature is high1 x may bake or vitrify !m1 j z 9 brick-mak+4 ,s$im5ts are consolidat$ by *emical action :5 m9]al sub/ances1 especially calcium c>bonate1 ! iron oxides1 & silica are deposit$ betwe5 ! p>ticles by infiltrat+ wat]s1 cem5t+ ! p>ticles toge!r4 ,?is pr9ciple is easily demon/rat$ exp]im5tally by tak+ "s loose s& & wett+ x repeat$ly ) a saturat$ solution ( "s soluble m9]al1 l salt or alum1 all[+ ! wat] to evaporate ea* "t be=e mak+ a fre% application4 ,! int]/ices betwe5 ! gra9s are gradually fill$ up1 & ! s& soon becomes a firm rock4 ,b ! /ud5t %\ld cle>ly und]/& t1 9 geology1 gravel1 s&1 & clay are j z truly rocks be=e _! consolidation z aft]4 ,x is pla9 !n t 9 ea* ( ! pr9cipal gr\ps ( fragm5tal rocks we mu/ recognize an unconsolidat$ division & a consolidat$ division4 7#a7 ,conglom]ate gr\p4--,! rocks belong+ 9 ?is gr\p we "k be=e consolidation z gravel1 & aft] consolidation z conglom]ate4 ,gravel4--,! pebbles1 z we h already se51 are usually1 ?\gh n always1 well r\nd$ or wat]-worn2 & !y may be ( any size f co>se gra9s ( s& to b\ld]s4 ,z a rule1 h[ev]1 ! l>g] pebbles1 especially1 are ( approximately uni=m size 9 ! same b$ or lay] ( gravel1 )1 ( c\rse1 suffici5t f9e mat]ial to fill ! int]/ices4 ,al?\gh ! same limit$ mass ( gravel may %[ ! wide/ possible range 9 *emical & m9]alogical composition1 yet h>d rocks are evid5tly m likely ?an s(t rocks to =m pebbles2 & h5ce qu>tz & qu>tz-be>+ rocks usually pr$om9ate 9 gravels4 ,specim5 #bh4 ,conglom]ate4--,consolidat$ gravel4 ,*ildr5 %\ld be l$ to an appreciation ( ?is po9t by a c>eful comp>ison ( ! =ms ( ! pebbles 9 ! gravel & conglom]ate4 ,! conglom]ate seems to conta9 a l>g] proportion ( f9e mat]ial ?an ord9>y gravel4 ,b ?is is because ! gravel is usually1 z ) our specim51 tak5 f ! surface ( ! bea*1 :]e1 ( c\rse1 ! pebbles are clean & sep>ate2 b if x _h rema9$ !re to be cov]$ by a subsequ5tly deposit$ lay]1 en\gh f9e /uff w\ld h be5 sift$ into ! holes to fill !m4 ,& 9 ! f9i%$ gravel1 j z 9 ! conglom]ate1 ! pebbles are usually closely pack$1 ) j suffici5t s& & clay1 or pa/e1 z ! mat]ial 9 :i* ! pebbles are imb$d$ is call$1 to fill ! int]/ices4 ,! pa/e is usually simil> 9 composition to ! pebbles1 ) ?is diff]5ce3 h>d mat]ials pr$om9ate 9 ! pebbles & s(t 9 ! pa/e4 ,/ratifi$ rocks g5]ally %[ ! /ratification 9 p>allel l9es or b&s diff]+ 9 color1 composition1 etc42 b no?+ l ?is c be detect$ 9 our specim5s ( conglom]ate2 & ! "q might be ask$1 ,h[ d we "k t ?is is a /ratifi$ rock8 ,9 answ]1 x c be said t our h&-specim5s appe> un/ratifi$ simply because ! rock is s co>se2 b :5 we look at l>ge masses1 & especially :5 we see x 9 place 9 ! qu>ry1 t p>allel arrangem5t ( ! mat]ial :i* we call /ratification is usually v evid5t2 & we (t5 see precisely ! same ?+ 9 gravel banks4 ,x is1 h[ev]1 :olly unnecess>y t we %\ld see ! /ratification 9 ord] to "k c]ta9ly t ?is is a /ratifi$ or aque\s rock1 because ! =ms ( ! pebbles %[ v pla9ly t !y h be5 fa%ion$ & deposit$ by mov+ wat]2 & we h 9 ! smalle/ specim5 pro( positive t our conglom]ate is a consolidat$ sea-bea*4 ,conglom]ate %[s ! same v>iations 9 composition & texture z gravel2 x may be compos$ ( almo/ any k9d ( mat]ial 9 pebbles ( almo/ any size4 ,we recognize two pr9cipal v>ieties ( conglom]ate bas$ on ! =ms ( ! pebbles2 if1 z is usual1 ^! are well r\nd$ & wat]-worn1 ! rock is true pudd+-/one 7specim5 #bi72 b1 if !y are angul>1 or %[ b little we>1 x is call$ breccia4 7#b7 ,ar5ace\s ,gr\p4--,! conglom]ate gr\p passes ins5sibly into ! ar5ace\s gr\p2 =1 f ! co>se/ gravel to ! f9e/ s&1 ! gradation is unbrok51 & e s&/one is m]ely a conglom]ate on a small scale4 ,s&4--,l gravel1 s& may be ( almo/ any composition1 b z a rule x is qu>tzose2 qu>tz1 on acc\nt ( its h>dness & ! abs5ce ( cleavage1 be+ bett] adapt$ ?an any o!r common m9]al to =m s&4 ,:]e ! composition ( a s& is n specifi$1 a qu>tzose s& is always und]/ood4 ,by exam9+ a typical s& ) a l5s1 & not+ ! glassy appe>ance ( ! gra9s1 & !n te/+ _! h>dness on a piece ( glass1 :i* !y w scrat* z easily z qu>tz1 ! pupil is readily conv9c$ t ea* gra9 is simply an angul> fragm5t ( qu>tz4 ,specim5 #cj4 ,s&/one4--,consolidat$ s&4 ,9 prov+ ?is1 *ildr5 w notice fir/ ! granul> or s&y appe>ance ( ! s&/one2 & !n1 ) ! l5s1 t ! gra9s 9 ! s&/one h ! same =ms z ! s&-gra9s4 ,! /ratification _c be se5 v di/9ctly 9 our h&-specim5s1 b 9 l>g] masses x is usually v pla91 z may be obs]v$ 9 ! blocks us$ = build+1 & /ill bett] 9 ! qu>ries4 ,h[ev]1 ev5 if ! /ratification 7 n visible to ! eye1 we c\ld h no d\bt t s&/one is a me*anically =m$ /ratifi$ rock2 because ! =m ( ! gra9s1 j z 9 ! conglom]ate1 tells u t4 ,_m s&/ones1 too1 conta9 ! fossil rema9s ( plants & animals1 & ^! are always reg>d$ z af=d+ positive pro( t ! rocks conta9+ !m belong to ! aque\s or /ratifi$ s]ies4 ,!re are _m v>ieties ( s&/one dep5d+ ^u diff]5ces 9 composition1 texture1 etc41 b we h n space to notice !m 9 detail4 ,9 s&/one1 j z 9 s&1 qu>tz is ! pr$om9ant con/itu5t1 al?\gh we sometimes f9d v>ieties compos$ l>gely or entirely ( feldsp>1 mica1 calcite1 or o!r m9]als4 ,specim5 #ca is an example ( ! ar*itectural v>iety kn[n z free/one1 :i* is m]ely a f9e-gra9$1 light-color$1 uni=m s&/one1 n v h>d1 & break+ ) ab\t equal fre$om 9 all directions4 ,! consolidation ( s&/ones is due *iefly to *emical action4 ,! cem5t+ mat]ials are commonly ei!r3 f]rug9\s 7iron oxides71 giv+ r$ or br[n s&/ones2 calc>e\s1 =m+ s(t s&/ones1 :i* eff]vesce ) acid if ! cem5t is abundant2 or silice\s1 mak+ v /rong1 light-color$ s&/ones4 ,f]rug9\s s&/ones are ! mo/ valuable = ar*itectural purposes2 =1 :ile n excessively h>d1 !y h a v durable cem5t4 ,silice\s s&/ones are too h>d2 & ! calc>e\s v>ieties crumble :5 expos$ to ! wea!r because ! cem5t is soluble 9 wat] conta9+ c>bon dioxide1 z all ra9-wat] does4 ,specim5 #cb is a good example ( a f]rug9\s s&/one1 & x is co>se en\gh s t we c see t ea* gra9 ( qu>tz is coat$ ) ! r$ oxide ( iron4 ,! mica scales visible "h & !re 9 ?is specim5 are int]e/+ z %[+ t ! gra9s are n necess>ily all qu>tz2 & x is important to obs]ve t ! mica 0 n made 9 ! s&/one1 b1 l ! qu>tz1 has come f "s old] rock4 ,qu>tzite4--,?is rock is simply an unusually h>d s&/one4 ,n[ ! h>dness ( any rock dep5ds ^u two ?+s3 7#a7 ! h>dness ( ! individual gra9s or p>ticles2 & 7#b7 ! firmness ) :i* !y are unit$ "o to ano!r4 ,!re=e1 ! h>de/ s&/ones mu/ be ^? 9 :i* gra9s ( qu>tz are comb9$ ) an abundant silice\s cem5t2 & t is precisely :at we h 9 a typical qu>tzite1 su* z specim5 #cc4 ,qu>tzite is di/+ui%$1 9 ! h&-specim51 f ord9>y qu>tz by its granul> texture 7comp>e specim5s #ae & #cc72 & ( c\rse 9 l>ge masses ! /ratification is an important di/+ui%+ feature4 #c4 ,argillace\s gr\p4--,j z ! conglom]ate gr\p %ades (f gradually into ! ar5ace\s gr\p1 s we f9d x difficult to draw any %>p l9e ( division betwe5 ! ar5ace\s gr\p & ! argillace\s1 b we pass f ! l>ge/ pebble to ! mo/ m9ute clay-p>ticle by an ins5sible gradation4 ,= ! sake ( conv5i5ce1 h[ev]1 we draw ! l9e at ! limit ( visibility1 & say t 9 ! true clay & slate ! individual p>ticles are invisible to ! nak$ eye2 9 o!r words1 ^! rocks h a p]fectly compact texture1 :ile ! two prec$+ gr\ps are *>act]iz$ by a granul> texture4 ,al?\gh clay1 l s& & gravel1 may be ( almo/ any composition1 yet x usually consi/s *iefly1 (t5 entirely1 ( ! m9]al kaol94 ,! reason = ?is is easily f\nd4 ,qu>tz resi/s bo? me*anical & *emical =ces1 & is r>ely r$uc$ to an impalpable f95ess2 b all ! o!r common m9]als1 su* z feldsp>1 hornbl5de1 mica1 & calcite1 on acc\nt ( _! cleavage & inf]ior h>dness1 are easily pulv]iz$2 b x is practically impossible t ?is %\ld happ5 )\t _! be+ brok5 up *emically at ! same "t4 ,decomposition foll[s dis9tegration2 &1 :ile calcite is completely dissolv$ & c>ri$ away1 ! o!r m9]als are r$uc$1 z we h se51 to impalpable hydr\s silicates ( alum9um1 i4e41 to kaol94 ,h5ce1 we f9d t ! fragm5tal rocks are compos$ pr9cipally ( two m9]als1 qu>tz & kaol91--! =m] pr$om9at+ 9 ! conglom]ate & ar5ace\s gr\ps1 & ! latt] 9 ! argillace\s gr\p4 ,clay4--,t kaol9 is ! basis ( common clay is prov$ by ! argillace\s odor1 :i* is s *>act]i/ic ( moi/ clay4 ,pure kaol9 clay is :ite & impalpable1 l ,*9a clay2 b pure clays are ! exception4 ,!y (t5 become co>se & gritty by admixture ) s&1 =m+ loam2 & !y also usually conta9 m or less c>bonace\s matt]1 :i* makes black clays2 or m or less f]r\s oxide1 :i* makes blue clays2 or m or less f]ric oxide1 :i* makes r$1 br[n1 & yell[ clays4 ,by mix+ ^! color+ mat]ials 9 v>i\s proportions1 almo/ any t9t may be expla9$4 ,clays are sometimes calc>e\s1 f ! pres5ce ( %ells & %ell-fragm5ts or ( pulv]iz$ lime/one4 ,^! usually eff]vesce ) acid1 & are commonly kn[n z m>l4 ,x is ! calc>e\s mat]ial 9 a pulv]ul5t & easily soluble condition t makes ! m>ls valuable z soils4 ,slate4--,consolidat$ clay4 ,! compact texture & argillace\s odor are usually suffici5t to prove ?is4 ,to get ! odor we ne$ simply to brea! ^u ! specim51 & !n smell ( x4 ,we f9d all degrees ( induration 9 clay4 ,x sometimes1 z e "o kn[s1 becomes v h>d by simple dry+2 b ?is is n slate1 & no am\nt ( m]e dry+ w *ange clay into slate2 =1 :5 moi/5$ ) wat]1 ! dri$ clay is easily br\ght back to ! pla/ic /ate4 ,to make a good slate1 ! induration mu/ be ! result ( pressure1 aid$ probably to "s ext5t by heat4 ,true slate1 !n1 is a p]man5tly indurat$ clay :i* w n soak up & become s(t :5 wet4 ,slate is usually easily scrat*$ ) a knife1 & x is di/+ui%$ f lime/one by its non-eff]vesc5ce ) acid4 ,z we %\ld expect1 x %[s precisely ! same v>ieties 9 color & composition z clay4 ,a good assortm5t ( colors is af=d$ by ! ro(+-slates4 ,specim5 #cd is a typical slate1 = x n only has a compact texture & argillace\s odor1 b x is v di/9ctly /ratifi$4 ,! /ratification is m>k$ by alt]nat+ b&s ( slightly diff]5t colors1 & is mu* f9] & m regul> ?an we usually obs]ve 9 s&/one1 & ( c\rse entirely unlike ! /ratification ( conglom]ate4 ,^! diff]5ces are *>act]i/ic4 ,"s slates1 h[ev]1 are s homog5e\s t ! /ratification is sc>cely visible 9 small pieces4 ,?us ! ro(+-slates 7specim5 #ce7 r>ely %[ ! /ratification2 = x is an important fact t ! ?9 lay]s into :i* ?is v>iety splits are entirely indep5d5t ( ! /ratification4 ,?is is ! /ructure kn[n z slaty cleavage2 x is n due to ! /ratification1 b is develop$ 9 ! slate subsequ5tly to its deposition1 by pressure4 ,"s ro(+-slates1 kn[n z ribbon-slates1 %[ b&s ( color across ! flat surfaces4 ,^! b&s are ! true b$d+1 & indicate ! absolute want ( con=mity betwe5 ?is /ructure & ! cleavage4 ,few rocks are ri*] 9 fossils ?an slate1 & ^! prove t x is a /ratifi$ rock4 ,slate :i* splits easily into ?9 lay]s p>allel ) ! b$d+ is kn[n z %ale4 ,porcela9ite4--,?is is clay or slate :i* has be5 bak$ or p>tially vitrifi$ by heat s z to h ! h>dness & texture ( porcela94 #b4 ,,*emically ,,& ,,organically ,,=m$ ,,rocks4--,we h already le>n$ t f a geological po9t ( view ! diff]5ces betwe5 *emical & organic deposition are n great1 ! process be+ ess5tially *emical 9 ea* case2 & s9ce ! lime/ones & "s o!r important rocks are deposit$ 9 bo? ways1 x is evid5tly n only unnatural1 b frequ5tly impossible1 to sep>ate ! *emically f ! organically =m$ rocks4 ,unlike ! fragm5tal rocks1 ! rocks ( ?is division n only admit1 b require1 a *emical classification4 ,?is is natural because !y are ( *emical orig92 & x is practicable because1 ) few exceptions1 only "o class ( m9]als is deposit$ at ! same "t 9 ! same place1--a v conv5i5t & important fact4 ,!re=e our arrangem5t w be m9]alogical1 ?us3-- 7#a7 ,coal ,gr\p4 7#b7 ,iron-ore ,gr\p4 7#c7 ,silice\s ,gr\p4 7#d7 ,calc>e\s ,gr\p4 7#e7 ,metamorphic ,gr\p 7,silicates74 ,mo/ ( ! silicate rocks are mix$1 i4e41 are ea* compos$ ( sev]al m9]als2 b "s silicate rocks & all ! rocks ( ! o!r divisions are simple1 ea* species consi/+ ( a s+le m9]al only4 7#a7 ,coal ,gr\p4--,^! are entirely ( organic orig91 & include two alli$ s]ies1 :i* are always m]ely ! m or less ext5sively trans=m$ tissues ( plants or animals2 viz43-- ,coals & ,bitum5s4--,at ! fir/ lesson we exam9$ a sample ( peat 7specim5 #h71 & consid]$ ! g5]al conditions ( its =mation1 peat be+ 9 e in/ance simply p>tially decay$ m>% vegetation4 ,x 0 also /at$ t1 z dur+ ! lapse ( "t ! trans=mation becomes m complete1 ! peat is *ang$ 9 succession to lignite1 bitum9\s coal1 an?racite1 & graphite4 ,! coals1 inde$1 make a v beautiful & p]fect s]ies1 :e!r we consid] ! composition--!re be+ a gradual1 progressive *ange f ! composition ( ord9>y woody fibre 9 ! newe/ peat to ! pure c>bon 9 graphite1--or ! degree ( consolidation & m9]alization--s9ce !re is a gradual passage f ! light1 por\s peat1 %[+ di/9ctly ! vegetable =ms1 to ! heavy cry/all9e graphite1 be>+ no trace ( its vegetable orig94 ,?is relation is easily appreciat$ by a *ild1 if a prop] s]ies ( specim5s is pres5t$4 ,! coals also make a *ronological s]ies1 graphite & an?racite occurr+ only 9 ! old] =mations1 & lignite & peat 9 ! new]1 :ile bitum9\s coal is f\nd 9 =mations ( int]m$iate age4 ,bitum9\s coal is ! typical1 ! repres5tative coal2 & f a good specim5 ( ?is v>iety we may le>n two important facts3-- 7#a7 ,t true coals1 no less ?an peat1 are ( vegetable orig94 ,to see ?is we mu/ look at ! flat or *>coal surfaces ( ! coal4 ,^! soil ! f+]s l *>coal1 & usually %[ ! vegetable =ms di/9ctly4 7#b7 ,t coals are /ratifi$ rocks4 ,^! dirty *>coal surfaces always co9cide ) ! /ratification1 be+ m]ely ! successive lay]s ( vegetation deposit$ & press$ toge!r to build up ! coal2 & :5 we look at ! edge ( ! specim5 ! /ratification %[s pla9ly en\gh4 ,! bitum5s =m a simil> ?\gh less p]fect s]ies1 beg9n+ ) ! organic tissues1 & end+1 9 ! op9ion ( "s ( ! be/ *emi/s & m9]alogi/s1 ) diamond4 ,9 fact ! coals & bitum5s =m two di/9ct b p>allel s]ies4 ,! coals are exclusively ( vegetable orig91 :ile ! bitum5s are l>gely ( animal orig94 ,! organic tissues 9 :i* ! two s]ies orig9ate are *emically simil>1--! animal tissues1 :i* produce ! light] =ms ( bitum51 h[ev]1 conta9+ m hydrog5 & less c>bon & oxyg5 ?an vegetable tissues2 :ile ! f9al t]ms1 z j %[n1 are probably *emically id5tical1 be+ pure c>bon1--graphite = ! coals & diamond = ! bitum5s2 s t ! entire process ( *ange 9 ea* s]ies is ess5tially c>bonization1 a gradual elim9ation ( ! gase\s elem5ts1 oxyg5 & hydrog51 until pure solid c>bon alone rema9s4 ,! pr9cipal diff]5ces betwe5 ! coals & bitum5s are ! foll[+3-- ,coals are ri* 9 c>bon1 ) "s oxyg5 & little hydrog54 ,bitum5s are ri* 9 hydrog51 ) "s c>bon & little or no oxyg54 ,coals are entirely insoluble4 ,bitum5s are soluble 9 e!r1 b5zole1 turp5t9e1 etc41 & ! solid =ms are soluble 9 ! m fluid1 naph?a-l v>ieties4 ,coals are nev] liquid1 & _c be melt$ or1 ) trifl+ exceptions1 ev5 s(t5$ by heat4 ,_m bitum5s are naturally liquid1 & all become s on ! application ( heat4 ,! coals p>take ( ! *>act]i/ics ( _! *ief con/itu5t elem5t1 c>bon1 ! mo/ ?or\ghly solid sub/ance kn[n2 :ile ! bitum5s simil>ly %[ ! influ5ce ( hydrog51 ! mo/ p]fectly fluid sub/ance kn[n4 ,! two bitum5s ( ! greate/ geological importance are asphaltum or m9]al pit* & petroleum2 b ^! sub/ances are too famili> to require any f>!r description "h4 7#b7 ,iron-ore ,gr\p4--,^! int]e/+ & important /ratifi$ rocks include ! ?ree pr9cipal oxides ( iron1--limonite1 hematite1 & magnetite1--z well z ! c>bonate ( iron1 sid]ite2 & ! rocks h ess5tially ! same *>act]i/ics z ! m9]als4 ,9 economical importance !y are second only to ! coals2 & ! hi/ory ( _! =mation ?r\gh ! ag5cy ( organic matt] is "o ( ! mo/ int]e/+ *apt]s 9 *emical geology 7see page #bf74 ,! ?ree oxides are easily di/+ui%$ f ea* o!r by ! colors ( _! p[d]s or /reaks1 & ! magnetism ( magnetite1 & f all o!r common rocks by _! high specific gravity4 ,magnetite is ! ri*e/ 9 iron1 & limonite ! poore/4 ,z reg>ds ! degree ( cry/allization & ord] ( occurr5ce 9 ! =mations1 !y =m a s]ies p>allel ) ! coal s]ies1 ?us3-- ,limonite1 nev] cry/all9e1 & f\nd 9 rec5t =mations4 ,hematite1 (t5 cry/all9e1 & f\nd 9 old] =mations4 ,magnetite1 always cry/all9e1 & f\nd 9 olde/ =mations4 ,sid]ite eff]vesces ) /rong acid2 & ?is sep>ates x f all o!r rocks1 except lime/one & dolomite2 & f ^! x is di/+ui%$ by its high specific gravity4 ,z a m9]al1 sid]ite is (t5 light color$2 b z a rock x is always d>k1 & usually black1 f admixture *iefly ( c>bonace\s matt]4 ,9 /udy+ dynamical geology1 we h le>n$ 7page #bh7 ! reason = ! intimate association ( sid]ite ) b$s ( coal1 & ?is acc\nts equally = ! c>bon conta9$ 9 ! rock itself4 ,! connection ( ?is rock ) ! coal-=mations adds mu* to its value z an ore ( iron4 ,f9ally1 ! iron-ores1 at lea/ :]e ( mu* economical importance1 are truly /ratifi$4 ,?is c (t5 be se5 9 h&-specim5s2 & is well %[n by _! relations to o!r rocks1 9 qu>ries & m9es2 & 9 _m cases1 = limonite & hematite1 by ! fossils :i* !y conta94 7#c7 ,silice\s ,gr\p4--,^! rocks are compos$ ( pure silica 9 ! =ms ( qu>tz & opal4 ,:5 fir/ deposit$1 :e!r organically1 l tripolite1 or *emically1 l silice\s tufa1 ! silice\s rocks are s(t & light1 & ! silica is 9 ! =m ( opal4 ,subsequ5tly x *anges to qu>tz1 & ! rocks assume ! mu* h>d] & d5s] =ms ( *]t & novaculite1 respectively4 ,tripolite or ,diatomace\s ,e>?4--,?is int]e/+ rock is s(t1 light1 & looks l clay2 b x is light]1 & ! argillace\s odor is fa9t or want+4 ,x does n eff]vesce ) acid4 ,h5ce1 x is nei!r clay nor *alk4 ,not)/&+ its s(tness1 x is really compos$ ( a h>d sub/ance1 viz41 silica1 9 ! =m kn[n z opal4 ,by rubb+ (f a little ( ! du/1 & exam9+ x "u ! microscope1 we easily prove t ! silica is ma9ly or entirely ( organic orig92 = ! du/ is se5 to be simply a mass ( m or less fragm5t>y organic rema9s1 occurr+ 9 great v>iety1 & ( wond]ful beauty & m9ut5ess4 ,!re are few rocks s unpromis+ on ! ext]ior1 & yet s beautiful )94 ,we h already le>n$ t ^! organic bodies are pr9cipally ,diatom cases1 ,radiol>ia %ells1 & ,sponge spicules4 ,we c =m "s idea ( _! m9ut5ess f ,ehr5b]g's e/imate t a s+le cubic in* ( pure tripolite conta9$ no less ?an #da1jjj1jjj1jjj organisms4 ,! lightness ( tripolite 7sp4 gr41 #a-a4e7 is due to ! facts t opal is a light m9]al 7sp4 gr41 #a4i-b4b71 & t _m ( ! %ells are holl[4 ,tripolite is a good example ( a s(t rock compos$ ( a h>d m9]al2 & x owes its value z a poli%+ mat]ial to ! fact t x consi/s ( a h>d m9]al 9 an exce$+ly f9e /ate ( division4 ,tripolite1 :5 pure1 is sn[-:ite2 b x is r>ely pure1 be+ commonly ei!r argillace\s or calc>e\s4 ,?is rock is n[ =m+ 9 ?\s&s ( places1 9 bo? fre% wat] & ! ocean4 ,fl9t & ,*]t4--,dur+ ! c\rse ( geological "t1 b$s ( tripolite are gradually consolidat$1 *iefly by p]colat+ wat]s1 :i* are con/antly dissolv+ & re-deposit+ ! silica2 &1 f9ally1 9 ! place ( a s(t1 e>?y rock1 we get a h>d1 fl9ty "o1 :i* we call fl9t if x occurs 9 ! new]1 or *]t if x occurs 9 ! old]1 geological =mations4 ,besides =m+ b$s ( ne>ly pure silica1 :i* we call tripolite1 ! microscopic silice\s organisms are diffus$ m or less abundantly ?r\gh o!r rocks1 especially *alk & lime/one4 ,9 su* cases ! consolidation ( ! silica implies its segregation also2 i4e41 ! silica dissolv$ by p]colat+ wat] is deposit$ only ab\t c]ta9 po9ts 9 ! rock1 build+ up r\nd$ concretions or nodules4 ,?us1 a silice\s lime/one becomes1 by ! segregation ( ! silica1 a pure lime/one conta9+ nodules ( *]t1 :i* are usually arrang$ 9 l9es p>allel ) ! /ratification4 ,specim5 #af is a fragm5t ( a fl9t-nodule f ! *alk-=mation ( ,engl&4 ,silice\s ,tufa4--,hot wat]1 & especially hot alkal9e wat]1 circulat+ ?r\gh ! e>?'s cru/1 is always *>g$ ) silica dissolv$ out ( ! rocks2 & :5 su* wat] issues on ! surface 9 a hot spr+ or geys]1 x is cool$ by contact ) ! air1 its solv5t p[] is dim9i%$ !reby1 & a l>ge "p ( ! silica is deposit$ ar\nd ! outlet z a sn[y-:ite por\s mat]ial call$ silice\s tufa4 ,silica deposit$ 9 ?is way is1 l organic silica1 always 9 ! =m ( opal4 ,silice\s tufa is di/+ui%$ f clay1 slate1 *alk1 & lime/one by ! same te/s z tripolite1 & f tripolite itself by ! abs5ce ( microscopic organisms4 ,novaculite4--,?r\gh ! action ( p]colat+ wat] & pressure1 silice\s tufa1 l tripolite1 becomes h>d] & d5s] & is ?us *ang$ to novaculite1 :i* holds ! same relation to *emically deposit$ silica t *]t & fl9t d to organically deposit$ silica4 ,! :ite novaculite obta9$ at ! ,hot ,spr+s ( ,arkansas1 & commonly kn[n z ,arkansas /one1 is a typical example ( ?is rock4 ,! rock :i*1 on acc\nt ( ! use to :i* x is put1 is kn[n z buhr-/one1 is also an excell5t example ( *emically deposit$ silica4 ,x is usually some:at por\s & fossilif]\s4 7#d7 ,calc>e\s ,gr\p4--,^! are ! lime-rocks1 includ+ ! c>bonate ( lime1 9 lime/one & dolomite1 ! sulphate ( lime1 9 gypsum1 & ! phosphate ( lime1 9 phosphate rock4 ,^! rocks are ev5 m closely connect$ 9 orig9 ?an 9 composition2 & x is = ?is reason t rock-salt1 :i* ( c\rse conta9s no lime1 is also includ$ 9 ?is gr\p4 ,lime/ones are =m$ abundantly 9 ! op5 sea1 ?r\gh ! accumulation ( %ells & corals2 b :5 portions ( ! sea become deta*$ f ! ma9 body & gradually dry up1 l ! ,dead ,sea & ,great ,salt ,lake1 dolomite1 gypsum1 & rock-salt are deposit$ 9 succession z *emical precipitates4 ,phosphate rock may be reg>d$ z a v>iety ( lime/one1 result+ f ! accumulation ( ! skeletons & excrem5t ( ! high] animals4 ,lime/one4--,?is is ! li?ologic or rock =m ( c>bonate ( lime or calcite1 & "o ( ! mo/ important1 int]e/+1 & useful ( all rocks4 ,al?\gh s simple 9 composition1--calcite be+ ! only ess5tial con/itu5t1--lime/one embraces _m di/9ct v>ieties1 & is really equival5t to a :ole family ( rocks4 ,a highly fossilif]\s lime/one1 su* z specim5 #ch1 is1 p]haps1 ! be/ v>iety ) :i* to beg9 ! /udy ( ! species4 ,! s(tness ( ! fossil %ells ( :i* ! rock is s l>gely compos$1 & ! fact t !y eff]vesce readily ) dilute acid1 proves t !y are /ill c>bonate ( lime2 & by apply+ ! acid m c>efully1 x c be se5 t ! compact matrix ( ! rock also eff]vesces1 consi/+ ( %ells m f9ely brok5 or comm9ut$ & mix$ ) m or less clay & o!r impurity1 almo/ ! entire rock be+ ( organic orig94 ,on ! coa/ ( ,florida1 & 9 _m o!r places1 we f9d beautiful examples ( %ell-lime/one n[ 9 process ( =mation4 ,^! are at fir/ v op5 & por\s1 because ! int]/ices betwe5 ! ne>ly entire %ells are n yet fill$ up ) small] fragm5ts & s&4 ,b :5 t is done1 we %all h a rock simil> to ! old fossilif]\s lime/one4 ,specim5 #cg4 ,! %ells & fragm5ts1 & ! gra9s ( calc>e\s s&1 are1 z a rule1 quickly cem5t$ toge!r by ! deposition ( c>bonate ( lime betwe5 !m2 s t lime/one is n[h]e obs]v$ occurr+ abundantly 9 an unconsolidat$ =m4 ,lime/one1 z a rule1 is n di/9ctly /ratifi$ 9 h&-specim5s1 b ( c\rse t x is a true s$im5t>y rock is abundantly prov$ by ! fossils2 & x goes almo/ )\t say+ t lime/one1 be+ necess>ily ma9ly compos$ ( organic rema9s1 mu/ be to a great] ext5t ?an any o!r rock ! great /ore-h\se ( fossils2 & 9 no o!r rock are ! fossils s well pres]v$ & p]fect z 9 lime/one4 ,nev]!less1 !re are ext5sive =mations ( lime/one conta9+ no disc]nible traces ( fossils4 ,& "s ( ^! non-fossilif]\s lime/ones1 too1 are ( v rec5t =mation4 ,"s ( ! mod]n coral-reefs1 = example1 are compos$ ( lime/one :i* 0 =m$ only ye/]day1 z x 71 & :i*1 f its mode ( =mation1 mu/ consi/ entirely ( corals2 & yet x %[s no trace ( its organic orig91 b is p]fectly compact1 or1 possibly1 cry/all9e4 ,?is frequ5t oblit]ation ( ! organic rema9s1 z well z ! p]fect consolidation ( ! rock1 is attribut$ to its solubility4 ,! calcium c>bonate is gradually dissolv$ by ! wat]1 & !n deposit$ 9 ! int]/ices 9 o!r p>ts ( ! rock4 ,specim5 #ci is t v>iety ( lime/one kn[n z *alk4 ,x is s(t & e>?y1 resembl+ bo? clay & tripolite1 b diff]+ f ! =m] 9 lack+ ! di/9ct argillace\s odor1 & f bo? by its lively eff]vesc5ce ) acids4 ,x appe>s to be entirely de/itute ( organic rema9s1 b ?is is a defect ( our vision & n ( ! rock2 =1 l ! tripolite1 x (t5 appe>s "u ! microscope to be little else ?an a mass ( %ells4 ,tripolite is a deposit built up ( ! silice\s %ells ( ,diatoms & ,radiol>ia1 :ile *alk is *iefly compos$ ( ! simil> b calc>e\s %ells ( ,=am9if]a4 ,our specim5 is f ! ,cretace\s =mation ( ,engl&2 b we h good reason to believe t *alk is n[ =m+ on a v ext5sive scale4 ,!re are millions ( squ>e miles 9 ! deep] p>ts ( ! ocean :]e ! dr$ge br+s up little else b a p]fectly impalpable1 gray1 calc>e\s slime or ooze4 ,:5 exam9$ microscopically1 ?is is se5 to be compos$ *iefly ( ,=am9if]a %ells1 & among ^! ! g5us ,globig]9a pr$om9ates2 s t ! deposit is frequ5tly call$ ,globig]9a ooze4 ,n[ ?is gray1 calc>e\s ooze1 :5 dri$ & compact$ by pressure1 makes a s(t1 :ite rock :i* c sc>cely be di/+ui%$ f *alk2 9 fact1 x is a mod]n *alk4 ,& !re seems no good reason to d\bt t ! deposition ( *alk has gone on cont9u\sly s9ce ,cretace\s "t--= sev]al millions ( ye>s at lea/4 ,specim5 #dj is also a :ite rock1 easily scrat*$ ) ! knife1 & eff]vesc+ freely ) acid1 & !re=e a v>iety ( lime/one4 ,b its texture is v diff]5t f ! o!r v>ieties we h /udi$4 ,x has a sp>kl+ surface1 :i* we expla9 by say+ t ! rock is cry/all9e4 ,x is1 9 fact1 a mass ( m9ute cry/als ( calcite4 ,! cry/all9e lime/ones h n always be5 cry/all9e1 b x is safe to assume t !y 7 orig9ally entirely uncry/all9e1 & 9 _m cases ri* 9 fossils2 b ! fossils h be5 ma9ly oblit]at$ by ! cry/allization4 ,cry/allization g5]ally 9 rocks is an indication ( great age1 s t we usually say cry/all9e rocks mu/ be old] ?an uncry/all9e rocks ( ! same composition2 & ?is is ma9ly true ) ! lime/ones4 ,:5 ! cry/allization is r f9e1 z 9 our specim51 resembl+ granulat$ sug>1 we h :at is commonly call$ sac*>oidal lime/one4 ,?is is ! typical m>ble4 ,m>ble is n a sci5tific "n1 & ! t]m is usually appli$ to any calc>e\s rock :i* w take a poli%1 & sometimes ev5 to rocks :i* are n calc>e\s at all4 ,9 ! section on dynamical geology1 we le>n$ t ! c>bonate ( calcium or calcite is deposit$ f ! sea-wat]1 & lime/ones =m$1 9 two ways3 fir/1 9 a purely *emical way1 :]e ! wat] becomes saturat$ ) calcite2 &1 second1 organically1 :]e ! calcium c>bonate is tak5 f ! wat] by m>9e organisms to =m _! %ells & skeletons1 & ! gradual accumulation ( ^! on ! ocean-floor builds up a lime/one4 ,z be=e /at$1 ! diff]5ce betwe5 ^! two me?ods ( deposition is n s great z x (t5 seems1 because we "k t ! animals nev] make ! c>bonate ( calcium :i* !y secrete1 b x comes into ! sea ready made ) ! dra9age f ! l&4 ,! lime/ones =m+ at ! pres5t "t are almo/ :olly organic2 b ! rock kn[n z calc>e\s tufa is an exception4 ,?is is =m$ "u ! same g5]al conditions z silice\s tufa1 b mu* m abundantly1 & 9 cold wat] z well z w>m2 because calcite is f> m soluble 7especially 9 wat] conta9+ c>bon dioxide7 ?an opal or qu>tz4 ,x is deposit$1 n only ar\nd ! m\?s ( spr+s1 b also along ! b$s ( ! /reams :i* !y =m1 envelop+ /ones1 roots1 grasses1 etc41 & build+ up usually a loose1 spongy mass hav+ a v *>act]i/ic turface\s texture4 ,! pr9cipal accessory m9]als occurr+ 9 lime/one are3 7#a7 kaol91 =m+ argillace\s or slaty lime/one1 :i* may be recogniz$ by ! argillace\s odor & d>k color2 7#b7 qu>tz1 =m+ silice\s or *]ty lime/one1 kn[n by its h>dness or by ! nodules ( fl9t or *]t2 7#c7 dolomite1 =m+ dolomitic or magnesian lime/one1 :i* eff]vesces less freely ) acid2 & 7#d7 s]p5t9e1 =m+ s]p5t9ic lime/one1 :i* is %>ply di/+ui%$ by ! gre5 gra9s ( s]p5t9e m+l$ ) ! :ite calcite4 ,a concretion>y texture is common ) lime/one4 ,if ! concretions are small1 l mu/>d-se$1 we call ! rock olite2 if l>g]1 l peas1 pisolite4 ,dolomite4--,if = calcite1 :i* is ! sole ess5tial con/itu5t ( all lime/one1 we sub/itute ! alli$ m9]al dolomite1 we h ! rock dolomite4 ,z might be inf]r$ f its composition1 dolomite is v closely relat$ to lime/one1 al?\gh !re are "s important diff]5ces4 ,physically1 ! two rocks diff] ab\t z ! two m9]als d4 ,dolomite is h>d] ?an lime/one1 & be+ also less soluble1 x resi/s ! action ( ! wea!r m4 ,dolomite1 if pure1 eff]vesces feebly1 or n at all1 ) cold dilute acid4 ,"h1 h[ev]1 we h to recognize ! fact t dolomite is r>ely pure2 b !re exi/s1 9 consequ5ce ( ! admixture ( calcite1 a p]fectly gradual passage f pure dolomite to pure lime/one1 & p>allel ) ?is e degree ( vigor 9 ! reaction ) acid4 ,h5ce1 x is entirely an arbitr>y matt] z to :]e we %all draw ! l9e betwe5 dolomitic lime/one & calc>e\s dolomite4 ,dolomite is a v mu* less abundant rock ?an lime/one1 &1 unlike lime/one1 x r>ely conta9s _m fossils1 & is nev] ( organic orig92 i4e41 !re are no organisms :i* secrete ! m9]al dolomite to =m _! h>d p>ts or skeletons4 ,l gypsum & rock-salt1 dolomite is probably nev] deposit$ 9 ! op5 ocean1 b only 9 clos$ bas9s4 ,l lime/one1 x occurs ) bo? ! compact & ! cry/all9e textures4 ,gypsum4--,:5 pure1 ?is rock 7specim5 #cf7 is id5tical ) ! m9]al gypsum 7specim5 #ag71 except t x is r>ely cry/all9e4 ,x is usually1 h[ev]1 n only p]fectly compact1 b m or less d>k-color$ f ! admixture ( clay & o!r impurities4 ,its mo/ notable *>act]i/ics are its s(tness1 ! abs5ce ( ! argillace\s odor1 except :]e x conta9s mu* clayey impurity1 & its non-eff]vesc5ce ) acids4 ,! fir/ two usually s]ve to di/+ui% x f slate1 :ile ! acid te/ sep>ates x readily f lime/one & all o!r c>bonate rocks4 ,! deposition ( gypsum is purely *emical1 & x occurs "u ab\t ! same physical conditions z ! deposition ( salt2 i4e41 9 dry+-up portions ( ! sea4 ,h5ce we usually f9d gypsum associat$ ) b$s ( rock-salt2 &1 s9ce dry+-up seas are few 9 numb]1 & small comp>$ ) ! :ole ext5t ( ! ocean1 we c easily und]/& :y nei!r rock-salt nor gypsum are abundant rocks1 except 9 a few localities4 ,rock-,salt4--,?is int]e/+ & useful rock1 z we h already le>n$1 is deposit$ 9 a purely *emical way1 & only 9 dry+-up portions ( ! sea1 l ! ,dead ,sea1 ,great ,salt ,lake1 etc4 ,9 "s p>ts ( ,europe !re are b$s ( solid rock-salt ov] a hundr$ feet ?ick4 ,phosphate ,rock4--,al?\gh n specially abundant or attractive1 ?is rock is ( great economic int]e/ & importance on acc\nt ( its ext5sive use z a f]tiliz]4 ,"u ! g5]al head ( phosphate rock are includ$3 7#a7 ! typical guano1 :i* is ! consolidat$ excrem5t ( c]ta9 m>9e birds inhabit+ 9 great numb]s small coral isl&s 9 ! dry or ra9less regions ( ! tropics2 7#b7 ! und]ly+ coral rock1 :i* is (t5 *ang$ to phosphate rock ?r\gh ! p]colation ( ! ra9-wat] fall+ on ! guano2 7#c7 accumulations ( ! bones & coprolites ( ! high] animals2 7#d7 phosphatic lime/ones f :i* ! c>bonate ( lime has be5 l>gely dissolv$ away1 leav+ ! m insoluble phosphate ( lime4 7#e7 ,metamorphic ,gr\p 7/ratifi$ silicates74--,all ! *emically & organically =m$ rocks :i* we h /udi$ up to ?is po9t are simple1 i4e41 !y consi/ ea* ( only "o ess5tial m9]al2 b mo/ ( ! rocks 9 ?is great gr\p ( silicates are mix$1 or consi/ ea* ( sev]al ess5tial m9]als4 ,qu>tz is ! only important con/itu5t ( ^! rocks :i* is n1 /rictly speak+1 a silicate1 b 9 a c]ta9 s5se x is also n an exception1 s9ce x may always be reg>d$ z an excess ( acid 9 ! rock4 ,?is gr\p ( /ratifi$ rocks compos$ ( silicate m9]als is ( exceptional importance1 fir/1 on acc\nt ( ! l>ge numb] ( species :i* x includes1 &1 second1 on acc\nt ( ! va/ abundance ( "s ( ! species4 ,^! are1 above all o!rs1 ! rocks ( :i* ! e>?'s cru/ is compos$4 ,) unimportant exceptions1 all ! rocks ( ?is gr\p are cry/all9e2 & !y con/itute ! pr9cipal "p ( :at is g5]ally includ$ "u ! t]m metamorphic rocks--a g5]al "n = all /ratifi$ rocks :i* h be5 s act$ ^u by heat1 pressure1 or *emical =ces z to make !m cry/all9e4 ,al?\gh ! cry/all9e lime/one1 dolomite1 iron-ores1 etc41 %[ u t metamorphic rocks are n want+ 9 ! o!r gr\ps4 ,z already expla9$1 ! metamorphic or cry/all9e /ratifi$ rocks are usually old] ?an ! correspond+ uncry/all9e rocks2 b a po9t ( great] importance "h is ?is3 ! developm5t 9 ! silicate rocks ( cry/all9e *>act]s has usually made x impossible to det]m9e ! me?od ( _! deposition1 :e!r me*anical or *emical4 ,9 a few cases1 z ) ! rock gre5s&1 we "k t ! deposition is *emical2 :ile x is equally c]ta9 t su* common silicate rocks z gneiss1 mica s*i/1 & _m o!rs1 (t5 result f ! cry/allization ( ord9>y me*anical s$im5ts1 l s&/one & conglom]ate4 ,we classify all ^! rocks z ( *emical orig91 h[ev]1 )\t consid]+ ! mode ( _! deposition1 because ! subsequ5t cry/allization is itself ess5tially a *emical process2 & t ju/ifies u 9 say+ t ^! rocks are made :at !y n[ are *iefly by ! action ( *emical =ces4 ,:atev] !y 7 orig9ally1 !y h become1 ?r\gh _! cry/allization1 rocks hav+ a def9ite m9]al composition :i* c be classifi$ *emically4 ,"s ( ! details ( ! classification ( ?is gr\p1 z %[n 9 ! table1 require explanation4 ,9 /udy+ ! silicate m9]als x 0 /at$ to be important to recognize two classes--! acidic & ! basic--! divid+ l9e fall+ 9 ! neighborhood ( #fj p] c5t4 ( silica4 ,?is division is important simply because ,nature has 9 a great degree kept ! acidic & basic m9]als sep>ate 9 ! rocks2 & few ?+s 9 li?ology are m important ?an ! di/9ction ( ! silicate rocks 9 :i* acidic m9]als pr$om9ate f ^? 9 :i* basic m9]als pr$om9ate4 ,! am\nt ( silica :i* any rock ( ?is gr\p conta9s is %[n at a glance by ! *>t4 ,! v]tical brok5 l9es1 ) ! figures at ! top1 indicate ! proportion ( silica1 :i* increases f #cj p] c5t4 on ! "r to #he p] c5t4 on ! left2 s t ! p]c5tage ( silica :i* a rock conta9s det]m9es its position1 ! acidic species be+ on ! left1 & ! basic on ! "r4 ,z mo/ ( ^! rocks are compos$ ( two or m m9]als mix$ 9 v v>i\s proportions1 !re is usually a wide range 9 ! p]c5tage ( silica :i* ! same species may conta92 & ?is is express$ 9 ea* case by ! l5g? ( ! dott$ l9e "u ! "n ( ! rock4 ,?us1 9 sy5ite1 ! silica ranges f #ee p] c5t4 to #fe p] c5t4 ,! horizontal l9e 9 ! *>t sep>ates ! gneisses1 conta9+ feldsp> z an ess5tial con/itu5t1 f ! s*i/s1 9 :i* feldsp> is want+1 except z an accessory con/itu5t4 ,we w take up ! gneisses fir/4 ,gneiss4--,?is is ! mo/ important ( all rocks4 ,x =ms n f> f "o-half ( ,new ,engl&1 & a v l>ge proportion ( ! e>?'s cru/4 ,! "n 7pron\nc$ same z nice7 is kn[n to h orig9at$ among ! ,saxon m9]s1 b its precise d]ivation is lo/ 9 obscurity4 ,to f9d out :at ?is v important rock is1 we w consult specim5 #da4 ,! fir/ glance %[s u t x is n1 l ! rocks we h j be5 /udy+1 compos$ ( a s+le m9]al1 b ( sev]al m9]als1 ! mo/ conspicu\s ( :i* is ! p9k feldsp>--or?oclase4 ,?is we recognize z a feldsp>3 7#a7 by its h>dness1 :i* is a little less ?an t ( qu>tz1 & di/+ui%es x f calcite1 a m9]al hav+ ! g5]al appe>ance ( feldsp>2 7#b7 by its color1 :i* sep>ates x f hornbl5de & augite2 & 7#c7 by its cleavage1 :i* di/+ui%es x easily f qu>tz4 ,f9ally1 we "k x is or?oclase1 & n plagioclase1 by its g5]al aspect1 & by its association ) an abundance ( qu>tz1 :i* is ! next mo/ important con/itu5t ( ! rock4 ,! qu>tz is less abundant ?an ! or?oclase1 & m easily ov]look$1 yet anyone famili> ) ! m9]al w n fail to recognize x4 ,x =ms small1 irregul>1 glassy gra9s1 entirely devoid ( cleavage1 & scrat*+ glass easily4 ,on wea!r$ surfaces ( ! rock ! or?oclase becomes s(t & *alky1 :ile ! qu>tz rema9s cle> & h>d1 & !n ! two m9]als are v easily di/+ui%$4 ,besides ^!1 !re are num]\s black1 ?91 gli/5+ scales1 :i* we c easily prove to be ela/ic1 & recognize z mica4 ,9 mo/ books on ! subject1 ^! ?ree m9]als--or?oclase1 qu>tz1 & mica--are set d[n z ! normal or ess5tial con/itu5ts ( gneiss4 ,b x is n[ recogniz$ by ! be/ li?ologi/s t we may h true gneiss )\t any mica2 or we may h hornbl5de 9 ! place ( mica4 ,qu>tz & or?oclase are ! only ess5tial con/itu5ts ( gneiss2 & :5 ^! alone are pres5t1 we h ! v>iety kn[n z b9>y gneiss4 ,! addition to ^! ess5tial con/itu5ts ( mica1 gives micace\s gneiss2 & ( hornbl5de1 hornbl5dic gneiss4 ,( ^! ?ree pr9cipal v>ieties1 ! micace\s gneiss is by f> ! mo/ common & important4 ,! mica may be ei!r ! :ite species1 muscovite1 or ! black species1 biotite2 b x is usually ! =m]4 ,or?oclase is ! pr$om9ant con/itu5t 9 all typical gneiss1 usually =m+ at lea/ "o-half ( ! rock4 ,! or?oclase may1 h[ev]1 be replac$ to a great] or less ext5t by albite1 or ev5 by oligoclase4 ,b we frequ5tly see ! t]m gneiss c>elessly1 or ignorantly1 appli$ to rocks :i* are de/itute ( feldsp>1 ?\gh hav+ ! g5]al aspect ( gneiss4 ,augite r>ely occurs 9 gneiss2 & h5ce1 :5 we obs]ve a gneiss conta9+ a black m9]al :i* we "k is ei!r augite or hornbl5de1 x is pretty safe to call x ! latt]4 ,mica & hornbl5de1 al?\gh ! pr9cipal1 are n ! only1 accessory m9]als 9 gneiss2 b ! foll[+ species are also ( common occurr5ce3 g>net1 cyanite1 t\rmal9e1 fibrolite1 epidote1 & *lorite4 ,gneisses1 z ! table indicates1 exhibit a wide range 9 ! proportion ( silica :i* !y conta91 v>y+ f #fj to #he p] c5t42 & !re is a concomitant v>iation 9 specific gravity1 f ab\t #b4e 9 ! mo/ acidic to #b4h 9 ! mo/ basic v>ieties4 ,t gneiss is a true1 /ratifi$ rock is v cle>ly %[n 9 specim5 #da2 b1 un=tunately1 ! /ratification is n always s evid5t z 9 ?is case4 ,! mica-scales1 x w be obs]v$1 lie p>allel ) ! /ratification1 & assi/ v mat]ially to make x visible2 & gneisses conta9+ little or no mica1 z well z "s t are ri* 9 mica1 frequ5tly appe> almo/ or q un/ratifi$4 ,^! obscurely /ratifi$ v>ieties are commonly kn[n z granitoid gneiss1 hav+ ! texture & g5]al aspect ( granite4 ,! s$im5t>y orig9 ( gneiss is also cle>ly prov$ by its int]/ratification ) und\bt$ s$im5t>y rocks1 su* z lime/one1 iron-ores1 graphite1 qu>tzite1 etc4 ,sy5ite4--,?is is a mu* abus$ t]m1 b1 z n[ employ$ by ! be/ li?ologi/s1 x is ! "n ( a rock hav+ a s+le ess5tial con/itu5t1 viz41 or?oclase4 ,sy5ite 9 its simple/ v>iety conta9s no?+ b or?oclase2 b 9 addition we usually h ei!r hornbl5de1 =m+ hornbl5dic sy5ite1 or mica1 =m+ micace\s sy5ite4 ,sy5ite1 x w be obs]v$1 is equival5t to gneiss ) ! qu>tz remov$2 b1 :ile gneiss is ! mo/ abundant ( all rocks1 sy5ite is a comp>atively r>e rock2 & ?is is simply ano!r way ( say+ t ne>ly all or?oclase is associat$ ) qu>tz4 ,by admixture ( qu>tz we get a p]fectly gradual passage f sy5ite to gneiss4 ,! or?oclase 9 sy5ite is m frequ5tly replac$ by plagioclase ?an x is 9 gneiss4 ,9 sy5ite1 too1 hornbl5de is mu* m abundant ?an mica2 al?\gh j ! opposite is true 9 gneiss4 ,&1 aga91 9 gneiss ! mica is pr9cipally muscovite2 b 9 sy5ite x is almo/ exclusively biotite4 ,augite is a common accessory 9 ! m basic sy5ite2 b g>net1 t\rmal9e1 & ! o!r accessory m9]als1 occurr+ s frequ5tly 9 gneiss1 are almo/ unkn[n 9 sy5ite4 ,! specific gravity ( sy5ite v>ies f #b4g to #b4i4 ,diorite4--,?is is a m important rock ?an sy5ite2 b x is ( analog\s1 ?\gh m basic1 composition1 conta9+ a s+le ess5tial con/itu5t1 viz41 plagioclase4 ,any ( ! tricl9ic feldsp>s may occur 9 ?is rock1 b oligoclase is mo/ common4 ,l sy5ite1 diorite usually conta9s hornbl5de1 (t5 9 l>ge proportion1 =m+ hornbl5dic diorite1 :i* sometimes passes into rocks compos$ entirely ( hornbl5de4 ,x also1 b less frequ5tly1 conta9s mica1 =m+ micace\s diorite4 ,! mica is usually biotite1 r>ely muscovite4 ,mica & hornbl5de also (t5 occur toge!r 9 diorite1 & ! same is true ( sy5ite & gneiss4 ,qu>tz is ( common occurr5ce 9 ! m acidic v>ieties ( diorite1 & augite 9 ! m basic4 ,?is is a good example ( a basic rock1 = all its normal con/itu5ts are basic2 b ! p]c5tage ( silica v>ies f #de 9 ^? v>ieties ri*e/ 9 labradorite & augite to #fj or m 9 ^? conta9+ m or less qu>tz & or?oclase4 ,!re is a correspond+ *ange ( color f d>k to light1 & ( specific gravity f #b4g to #c4a4 ,diorite is n ri* 9 accessory m9]als2 besides ^? already m5tion$1 ! mo/ important are *lorite1 epidote1 pyrite1 & magnetite4 ,few rocks are m cle>ly /ratifi$ ?an diorite1 :e!r we consid] ! h&-specim51 or its relations to o!r =mations4 ,x is an abundant rock 9 ,new ,engl&4 ,norite4--,l diorite1 ?is is ess5tially a plagioclase rock2 b !re are1 nev]!less1 important diff]5ces4 ,! plagioclase 9 diorite is ma9ly ! m acidic species1 l oligoclase2 :ile 9 norite ! m basic species1 su* z labradorite & anor?ite1 pr$om9ate4 ,hornbl5de1 :i* we h obs]v$ to be an important & r con/ant con/itu5t ( diorite & sy5ite1 is mu* less abundant 9 norite2 b its place is tak5 by augite & ! alli$ m9]als1 hyp]/h5e & en/atite4 ,black mica is common 9 norite2 b :ite mica1 or?oclase1 & qu>tz r>ely occur4 ,norite is ! mo/ basic ( all ! feldspa?ic rocks1 z gneiss is ! mo/ acidic2 :ile sy5ite & diorite /& z connect+ l9ks1 =m+ a gradual passage betwe5 ! two extremes4 ,?us1 9 pass+ f gneiss to norite1 we h obs]v$ a gradual dim9ution ( ! qu>tz1 a gradual *ange 9 feldsp> f or?oclase to ! mo/ basic plagioclase2 at fir/ a gradual increase 9 hornbl5de1 & !n a gradual *ange f hornbl5de to augite2 &1 f9ally1 a gradual sub/itution ( black mica = :ite4 ,! am\nt ( silica has decreas$ ov] #dj p] c5t42 & ! specific gravity has increas$ f #b4e 9 ! lighte/ gneiss to at lea/ #c4b 9 ! heavie/ norite4 ,we h also pass$ f light color$ rocks to d>k2 & f ^? resi/+ atmosph]ic action to ^? easily decompos$4 ,! mo/ *>act]i/ic accessory con/itu5ts ( norite1 besides ^? already m5tion$1 are magnetite & *rysolite2 ?\gh g>net1 s]p5t9e1 & pyrite (t5 occur4 ,9 texture1 ?is rock v>ies f compact to v co>sely cry/all9e4 ,! specim5 ( labradorite 7,no4 #bc71 f ! norite ( ,labrador1 af=ds "s idea ( ! co>s5ess ( ! cry/allization 9 mu* ( ?is rock4 ,x is n a common rock1 except 9 c]ta9 regions1 ! be/ kn[n ( :i* 9 ea/]n ,nor? ,am]ica are ! coa/ ( ,labrador1 v>i\s po9ts 9 ,canada nor? ( ! ,/4 ,lawr5ce1 & ! ea/]n bord] ( ! ,adirondack ,m\nta9s4 ,9 h&-specim5s1 norite r>ely appe>s /ratifi$2 b 9 ! solid l$ges ! /ratification is (t5 z di/9ct z c\ld be desir$4 ,_m li?ologi/s call ! rocks "h designat$ norite gabbro1 & class !m all 9 ! eruptive division z ess5tially a co>se v>iety ( diabase4 ,9 a simil> mann]1 diorite & sy5ite are d5i$ a place 9 ! s$im5t>y s]ies4 ,b ! /ratifi$ plagioclase rocks seem to h z /rong a claim to recognition z gneiss4 ,we turn n[ to ! important & int]e/+ division ( ! non-feldspa?ic rocks or s*i/s4 ,mica ,s*i/4--,?is is1 next to gneiss1 ! mo/ abundant rock 9 ,new ,engl&4 ,specim5 #dc is a typical example1 & f x we c readily le>n :at mica s*i/ is4 ,a glance suffices to %[ t x is *iefly compos$ ( mica1 b n entirely2 =1 on c>efully exam9+ ! edges ( ! specim51 we _c fail to see ?9 lay]s ( h>d1 glassy qu>tz int]wov5 ) ! mica4 ,! qu>tz lay]s are %ort & ov]lapp+1 & we h "h a good illu/ration ( ! s*i/ose texture2 ?is is1 9 fact1 a typical s*i/4 ,mica s*i/ usually consi/s1 z 9 ?is in/ance1 ( mica & qu>tz2 b x may be compos$ ( mica alone2 & sometimes kaol9 or clay takes ! place ( ! qu>tz1 =m+ argillace\s mica s*i/4 ,! mica 9 ! latt] is usually 9 v f9e scales & r inconspicu\s1 & ! rock (t5 passes into ord9>y clay slate4 ,simil>ly1 :5 ! mica becomes defici5t 9 ! qu>tzose mica s*i/1 a passage into ord9>y qu>tzite is ! result4 ,a little feldsp> is sometimes pres5t 9 ! rock1 :i* ?us passes into micace\s gneiss4 ,specim5 #dc conta9s sev]al cry/als ( r$ g>net1 giv+ ! v>iety g>netif]\s mica s*i/4 ,!re is no o!r rock t conta9s su* a l>ge v>iety ( beautiful accessory m9]als z mica s*i/2 & = ! m9]alogi/ x is "o ( ! mo/ attractive rocks4 ,few rocks are m di/9ctly /ratifi$2 & ! /ratification c usually be obs]v$ 9 h&-specim5s4 ,! mica 9 ^! rocks may be ei!r muscovite or biotite1 or bo?2 b ! =m] is mo/ common4 ,no rock %[s a great] v>iation 9 ! p]c5tage ( silica :i* x conta9s ?an mica s*i/1 z we pass f v>ieties :i* are ne>ly all qu>tz to ^? :i* are ne>ly all mica4 ,closely relat$ to mica s*i/ is ! rock n[ kn[n z hydromica s*i/1 9 :i* ! ord9>y anhydr\s micas are replac$ by hydromica4 ,x is di/+ui%$ f mica s*i/ by be+ some:at s(t]1 less h>% to ! t\*1 & less lu/r\s4 ,x is to be reg>d$ usually z an incipi5t mica s*i/1 :i* has n yet become anhydr\s2 ?\gh x may sometimes be j ! rev]se2 viz43 an old mica s*i/ :i* has become hydrat$ ?r\gh ! action ( meteoric wat]s4 ,x conta9s few] accessory m9]als ?an mica s*i/4 ,hornbl5de ,s*i/4--,?is is a /ratifi$ aggregate ( hornbl5de & qu>tz4 ,! qu>tz is granul> & 9 ?9 lay]s1 z 9 mica s*i/2 b ! micace\s /ructure is want+1 & consequ5tly ! rock does n cleave readily 9 ! direction ( ! b$d+4 ,! hornbl5de is mo/ly f9ely cry/all9e1 b sometimes occurs 9 l>ge1 blad$ cry/als4 ,g>net & "s o!r m9]als are ( common occurr5ce 9 ! rock2 b x is n ri* 9 accessories l mica s*i/4 ,! *ief difficulty 9 recogniz+ ?is rock consi/s 9 det]m9+ :e!r ! :ite m9]al is all qu>tz or p>tly feldsp>4 ,9 ! latt] case1 ( c\rse1 x becomes a hornbl5dic gneiss4 ,amphibolite 7,hornbl5de ,rock74--,?is is ! "n appli$ to a rock hav+ hornbl5de z its sole ess5tial con/itu5t4 ,hornbl5de s*i/ sometimes passes into amphibolite1 ?r\gh ! abs5ce ( qu>tz2 & s does diorite1 :5 ! feldsp> is defici5t or want+4 ,specim5 #bj1 ?\gh small1 is a typical example ( ?is rock4 ,! physical & *emical *>act]i/ics are ess5tially ! same z = ! m9]al hornbl5de4 ,! texture v>ies f co>sely to f9ely cry/all9e4 ,! cry/als are usually %ort & ?ick1 & lie 9 all directions 9 ! rock1 :i* is ?us v massive1 ! s*i/ose texture be+ entirely want+1 & ! /ratification r>ely %[+ 9 small masses4 ,biotite is a common accessory 9 amphibolite1 & g>net & magnetite frequ5tly occur4 ,by ! sub/itution ( augite = hornbl5de1 9 ! description ( amphibolite1 we get ! mu* r>]1 b o!rwise v simil>1 rock1 pyrox5ite4 ,talc ,s*i/ 7,/eatite or ,soap/one74--,al?\gh n abundant1 ?is is a useful & famili> rock4 ,! composition is impli$ 9 ! "n2 & by comp>+ x ) ! specim5 ( talc 7,no4 #eh7 we c readily see t !y are ess5tially id5tical4 ,typical talc s*i/ is pure talc2 b ! talc is (t5 mix$ ) m or less qu>tz or feldsp>2 & mica1 *lorite1 hornbl5de1 g>net1 & o!r m9]als are ( common occurr5ce4 ,?is rock embraces two di/9ct v>ieties1 ! massive & ! s*i/ose1 or foliat$4 ,! =m] is ! common soap/one 7specim5 #ga71 :i* is a confus$ mass ( cry/als ly+ 9 all directions1 & ) no visible /ratification 9 ! small mass4 ,9 ! latt]1 z 9 specim5 1 ! talc scales lie 9 p>allel planes1 giv+ ! rock a micace\s /ructure1 & caus+ x to split easily 9 ! direction ( ! /ratification4 ,! cleavage surfaces are (t5 wavy or corrugat$2 & ! same is true ( all s*i/ose rocks4 ,talc s*i/ is easily di/+ui%$ f all o!r rocks by its light-grayi% or gre5i% color1 comb9$ ) its extreme s(tness1 & its smoo?1 slipp]y feel4 ,*lorite ,s*i/4--,! "o ess5tial con/itu5t ( ?is rock is *lorite1 & ! m9]al specim5 7,no4 #bf7 answ]s equally well z an example ( ! rock4 ,z ) talc s*i/1 qu>tz1 feldsp>1 & hydromica are r>ely entirely abs5t4 ,besides ^!1 ! pr9cipal accessories are hornbl5de1 magnetite1 g>net1 & epidote4 ,?is rock also agrees ) talc s*i/ 9 pres5t+ two pr9cipal v>ieties1 ! massive & ! s*i/ose4 ,x is easily di/+ui%$ f talc s*i/ by its d>k] color & /reak1 :i* are v *>act]i/ic2 :ile its gre5 color1 s(tness1 & unctu\s feel sep>ate x f all o!r rocks4 ,?is is ! mo/ basic ( all ! silicate rocks2 b1 9 consequ5ce ( conta9+ a l>ge proportion ( wat]1 x is n ! heavie/4 ,x is1 9 fact1 int]e/+ & important to obs]ve t all ^! hydr\s silicate rocks--talc s*i/1 *lorite s*i/1 gre5s&1 & s]p5t9e--are di/9ctly light] 9 ea* case ?an anhydr\s rocks conta9+ ! same proportion ( silica4 ,!y are also notable1 z a class1 = _! s(tness1 smoo? feel1 & gre5 color4 ,s]p5t9e4--,z ! "n implies1 ?is rock is simply ! m9]al s]p5t9e occurr+ 9 l>ge masses1 & its *>act]i/ics are precisely ! same4 ,x is f9e-gra9$1 massive1 compact1 r s(t1 b v t\gh1 & v>ies 9 color f v d>k gre5 to light gre5i%-yell[4 ,! d>k colors pr$om9ate1 & specim5 #be is a typical example4 ,s]p5t9e is (t5 intimately associat$ ) lime/one & dolomite4 ,! :ite ve9s runn+ irregul>ly ?r\gh ! v>iety kn[n z ,v]d ,antique ,m>ble1 h[ev]1 are n calcite1 z commonly suppos$1 b magnesite4 ,!y d n eff]vesce freely ) cold1 dilute acid1 = ! entire rock is magnesian1 & x is probable h be5 at "o "t simply cracks along :i* wat] hold+ c>bon dioxide has p5etrat$1 *ang+ ! magnesia f a silicate to a c>bonate4 ,geologi/s 71 at "o "t1 almo/ unanim\s 9 ! op9ion t all s]p5t9e is ( eruptive orig92 b n[ x is conc$$ by ! great majority to be 9 "s cases a s$im5t>y rock4 ,x is f\nd int]/ratifi$ ) gneiss1 lime/one1 all ! s*i/s1 & _m o!r /ratifi$ rocks4 ,:5 occupy+ ! position ( an eruptive x is nev] an orig9al rock2 b has be5 =m$ by ! alt]ation1 9 situ1 ( "s basic anhydr\s rock1 mo/ commonly oliv9e basalt4 ,gre5s&4--,?is rock 7specim5 #bg7 consi/s *iefly ( ! m9]al glauconite1 m+l$ usually ) m or less s&1 clay1 or calc>e\s matt]4 ,x is usually v friable1 or 9 an entirely unconsolidat$ /ate4 ,x is mo/ abundant 9 ! new] geological =mations1 especially ! ,cretace\s & ,t]ti>y2 & is1 p]haps1 ! only "o ( ! /ratifi$ silicate rocks n[ =m+ on an ext5sive scale 9 ! ocean4 ,its value z a f]tiliz]1 = :i* purpose x is ext5sively employ$1 is due to ! pota% t x conta9s4 ,foll[+ is a sy/ematic summ>y ( ! m9]alogical composition ( ! rocks ( ?is great division ( silicates2 & ?is1 comb9$ ) ! classification on page #fi1 pres5ts 9 a cond5s$ =m all ! m important facts conta9$ 9 ! prec$+ descriptions4 ,only ! m con/ant & normal con/itu5ts ( ! species are enum]at$ 9 ea* case3-- ,names ( ,species4 ,con/itu5t ,m9]als4 ---------------------------------------- ---------------- ,or?oclase & ,qu>tz4 ,gneiss ,or?oclase1 ,qu>tz1 & ,mica4 ,or?oclase1 ,qu>tz1 & ,hornbl5de4 ---------------------------------------- ---------------- ,or?oclase4 ,sy5ite ,or?oclase & ,hornbl5de4 ,or?oclase & ,mica4 ---------------------------------------- ---------------- ,plagioclase 7*iefly ,oligoclase74 ,diorite ,plagioclase & ,hornbl5de4 ,plagioclase & ,mica4 ---------------------------------------- ---------------- ,plagioclase 7*iefly ,labradorite74 ,norite ,plagioclase & ,augite 7,diallage74 ,plagioclase & ,mica4 ---------------------------------------- ---------------- ,mica4 ,mica ,s*i/ ,mica & ,qu>tz4 ,mica & ,kaol94 ---------------------------------------- ---------------- ,hornbl5de ,s*i/ ,hornbl5de & ,qu>tz4 ---------------------------------------- ---------------- ,amphibolite ,hornbl5de4 ,pyrox5ite ,pyrox5e4 ---------------------------------------- ---------------- ,talc ,s*i/ ,talc4 ---------------------------------------- ---------------- ,*lorite ,s*i/ ,*lorite4 ---------------------------------------- ---------------- ,s]p5t9e ,s]p5t9e4 ---------------------------------------- ---------------- ,gre5s& ,glauconite4 #b4 ,eruptive or ,un/ratifi$ ,rocks4 ,! rocks ( ?is great class are =m$ by ! cool+ & solidification ( mat]ials t h come up f a great dep? 9 ! e>?'s cru/ 9 a melt$ & highly heat$ condition4 ,:5 ! fissures 9 ! e>?'s cru/ rea* d[n to ! great res]voirs ( liquid rock1 & ! latt] wells up & ov]fl[s on ! surface1 =m+ a volcano1 !n we may1 z 0 po9t$ out on page #cc1 divide ! eruptive mass into two p>ts3 fir/1 t :i* has actually fl[$ out on ! surface1 & cool$ & solidifi$ 9 contact ) ! air1 =m+ a lava fl[2 second1 t :i* has fail$ to rea* ! surface1 b cool$ & solidifi$ 9 ! fissure1 =m+ a dike4 ,lava fl[s or volcanic rocks & dikes or plutonic rocks are id5tical 9 composition2 b !re is a va/ diff]5ce 9 texture1 due to ! widely diff]5t conditions "u :i* ! rocks h solidifi$4 ,! dike or fissure rocks solidify "u enorm\s pressure1 & ?is makes !m heavy & solid--free f pores4 ,!y are surr\nd$ on all sides by w>m rocks3 ?is causes !m to cool v sl[ly1 & all[s ! v>i\s m9]als "t to cry/allize4 ,o!r ?+s be+ equal1 ! sl[] ! cool+ ! co>s] ! cry/allization2 & h5ce1 ! great] ! dep? bel[ ! surface at :i* ! cool+ takes place1 ! co>s] ! cry/allization4 ,! volcanic rock1 on ! o!r h&1 cools "u v slight pressure2 & ! /eam1 :i* exi/s abundantly 9 ne>ly all igne\s rocks at ! "t ( _! eruption1 is able to exp&1 =m+ innum]able small vesicles or bubbles 9 ! liquid lava2 & ^! rema9 :5 x has become solid4 ,cool+ 9 contact ) ! air1 ! lava cools quickly1 & has b little *ance = cry/allization4 ,h5ce1 to sum up ! matt]1 we say3 plutonic rocks are solid & cry/all9e2 & volcanic rocks are usually por\s or vesicul>1 & uncry/all9e4 ,z we desc5d into ! e>?'s cru/1 x is p]fectly manife/ t ! volcanic mu/ %ade (f ins5sibly into ! dike rocks1 & we f9d x impossible to draw any b an arbitr>y plane ( division betwe5 !m2 b ?is is no argum5t aga9/ ?is classification1 =1 z already /at$1 all is gradation 9 geology1 & we exp]i5ce j ! same difficulty 9 draw+ a l9e betwe5 conglom]ate & s&/one1 or betwe5 gneiss & mica s*i/1 z betwe5 ! dike rocks & volcanic rocks4 ,we w n[ obs]ve to :at ext5t ! di/9ctions betwe5 ^! two great classes ( eruptives c be trac$ 9 ! rocks !mselves1 beg9n+ ) ! dike rocks4 ,b fir/ x is important to notice ! g5]al fact1 cle>ly express$ 9 ! classification1 t1 ) p]haps "s trifl+ exceptions :i* ne$ n be m5tion$ "h1 all eruptive rocks are silicates1 & ne>ly all are feldspa?ic silicates4 ,!y are ( def9ite m9]alogical composition1 &1 l ! *emically & organically =m$ /ratifi$ rocks1 c be classifi$ *emically4 ,b1 al?\gh !re are eruptives correspond+ closely 9 composition to ! feldspa?ic silicates1 :i* we h j /udi$1 we f9d among !m little to repres5t ! non-feldspa?ic silicates1 & no?+ correspond+ 9 composition to ! lime/ones1 dolomites1 gypsum1 fl9t1 tripolite1 silice\s tufa1 iron-ores1 bitum5s or coals4 #a4 ,,plutonic 7,,dike7 ,,rocks4--,^! are also kn[n z ! anci5t eruptive rocks1 & = ?is reason3 ,x is impossible1 ( c\rse1 = u to obs]ve !m except :]e !y occur on or ne> ! e>?'s surface4 ,b1 s9ce !y are =m$ :olly bel[ ! surface1 & usually at great dep?s 9 ! e>?1 x is evid5t t !y c appe> on ! surface only z ! result ( enorm\s erosion2 & erosion is a sl[ process1 dem&+1 9 ^! cases1 _m ?\s&s or millions ( ye>s4 ,!re=e1 ! m anci5t dike rocks alone are )9 our rea*2 ^? ( rec5t =mation be+ /ill deeply buri$ 9 ! e>?'s cru/4 ,x foll[s1 z a coroll>y to ?is explanation1 t ! co>s5ess ( ! cry/allization ( any dike rock mu/ be a r\gh measure ( its age & ( ! am\nt ( erosion :i* ! region has suff]$ s9ce its eruption4 ,z reg>ds composition1 ! dike rocks pres5t1 z already /at$1 ess5tially ! same comb9ations ( m9]als z ! feldspa?ic silicates ( ! /ratifi$ s]ies1 b occurr+ "u diff]5t physical conditions & hav+ a widely diff]5t orig94 ,! only important diff]5ce 9 texture betwe5 ! two classes ( rocks is t ! s$im5t>y rocks are /ratifi$ & ! dike rocks are n2 & :5 we consid] t ! dike rocks sometimes pres5t a lam9at$ /ructure t resembles /ratification1 :ile ! s$im5t>y rocks frequ5tly appe> un/ratifi$1 x is easy to und]/& :y1 9 ! abs5ce ( any m>k$ diff]5ce 9 composition1 geologi/s h (t5 f\nd x difficult to di/+ui% ! two classes ( rocks4 ,we also f9d "h ! explanation & ! ju/ification ( ! fact t ! names ( ! dike rocks are 9 mo/ cases ! same z ^? ( ! s$im5t>y rocks ( simil> composition4 ,granite4--,granite 7f ! ,lat9 granum1 a gra97 is a cry/all9e-granul> rock1 agree+ 9 composition ) gneiss4 ,! ess5tial con/itu5ts are qu>tz & or?oclase2 & :5 !y alone are pres5t we h ! v>iety b9>y granite4 ,mica1 h[ev] 7commonly muscovite1 sometimes biotite1 & frequ5tly bo?7 is usually add$ to ^!1 =m+ micace\s granite 7specim5 #dd72 & (t5 hornbl5de1 =m+ hornbl5dic granite 7specim5 #de74 ,! or?oclase is sometimes replac$ 9 "p by tricl9ic species1 especially albite & oligoclase4 ,accessory m9]als are n s abundant 9 granite z 9 gneiss2 b1 besides ^? nam$1 g>net1 t\rmal9e1 pyrite1 apatite1 & *lorite are mo/ common4 ,or?oclase is always ! pr$om9ant +r$i5t2 &1 except :5 !re is mu* hornbl5de pres5t1 usually det]m9es ! color ( ! granite4 ,?us1 specim5s #dd & #de are gray because !y conta9 gray or?oclase2 :ile all r$ granites conta9 r$ or p9k or?oclase4 ,! qu>tz has usually be5 ! la/ ( ! con/itu5ts to cry/allize or solidify2 &1 hav+ be5 ?us oblig$ to adapt itself to ! cont\rs ( ! or?oclase & mica1 x is r>ely obs]v$ 9 di/9ct cry/als4 ,9 texture1 ! granites v>y f p]fectly compact v>ieties1 approa*+ petrosilex1 to ^? :i* are s co>sely cry/all9e t s+le cry/als ( or?oclase measure sev]al in*es 9 l5g?4 ,( c\rse "o ( ! mo/ important ?+s to be obs]v$ ab\t granite1 especially 9 comp>+ x ) gneiss1 is ! complete abs5ce ( any?+ l /ratification2 t1 z be=e /at$1 be+ ! only important di/9ction betwe5 ! two rocks4 ,gneiss is ! mo/ abundant ( all /ratifi$ rocks1 & granite /&s 9 ! same relation to ! eruptive s]ies4 ,sy5ite4--,?is is an in/ance :]e /ratifi$ & eruptive rocks1 agree+ 9 composition1 h ! same "n4 ,t rocks consi/+ ( or?oclase1 ( or?oclase & hornbl5de1 or ( or?oclase & mica1 i4e41 hav+ ! composition ( sy5ite1 d occur 9 bo? ! eruptive & /ratifi$ s]ies !re c be no d\bt4 ,!y %\ld1 h[ev]1 h di/9ct names on acc\nt ( _! unlike orig9s2 & w\ld h b = ! practical difficulty 9 det]m9+1 9 _m cases1 :e!r ! rock is /ratifi$ or n4 ,! be/ t we c d n[1 :5 we desire to be specific1 & h ! necess>y in=mation1 is to say /ratifi$ sy5ite or eruptive sy5ite1 z ! case may be4 ,diorite4--,"h1 aga91 we f9d id5tity ( names1 z well z ( composition1 betwe5 ! two great s]ies4 ,eruptive diorite is an abundant & well kn[n rock1 & consi/s ( ! same m9]als z /ratifi$ diorite comb9$ 9 ! same proportions4 ,diorite includes a l>ge "p ( ! dike rocks commonly kn[n z 8trap0 & 8gre5/one40 ,! pr9cipal accessories are *lorite1 epidote1 pyrite1 magnetite1 apatite1 & qu>tz4 ,! texture v>ies f p]fectly compact or felsitic to co>sely cry/all9e2 av]ag+1 h[ev]1 less co>se ?an sy5ite & granite4 ,diabase4--,by ref]r+ to ! classification x w be se5 t diabase occupies ! same position among ! dike rocks z norite among ! /ratifi$ rocks4 ,l norite x consi/s usually ( ! m basic v>ieties ( plagioclase ) or )\t augite1 diallage1 or hyp]/h5e4 ,augite1 or "o ( its repres5tatives1 is usually pres5t1 & is (t5 ! pr9cipal con/itu5t4 ,specim5 #a %[s a some:at equal developm5t ( ! feldsp> & augite4 ,! "n gabbro is sometimes appli$ to ! co>s] & m feldspa?ic diabases1 & especially to ^? conta9+ diallage or hyp]/h5e 9 ! place ( common augite4 ,9 ! op9ion ( "s high au?orities1 h[ev]1 x is unnecess>y to recognize two species "h2 & x makes ! classification m simple & symmetrical n to d x4 ,! pr9cipal accessories 9 diabase are biotite1 *lorite1 magnetite1 pyrite1 calcite1 & oliv9e4 ,*lorite is (t5 an important con/itu5t1 giv+ ! rock a gre5i% aspect2 b "h1 z well z 9 diorite1 ! *lorite is due *iefly or entirely to ! alt]ation ( ! augite & feldsp>2 & ! *loritic v>ieties ( diorite & diabase toge!r make up ! old species 8gre5/one40 ,simil>ly1 ! m compact & d>k] v>ieties ( ^! two rocks1 =m+ regul>1 wall-l dikes1 are kn[n z 8trap40 ,specim5 #df4 ,9 consequ5ce ( _! m basic composition1 diabase & diorite are usually /rongly contra/$ ) granite & sy5ite 9 color & specific gravity1 be+ d>k] & heavi]4 ,! basic rocks1 too1 decay mu* m readily ?an ! acidic4 #b4 ,,volcanic ,,rocks4--,z reg>ds composition1 we %all f9d no?+ new 9 ! volcanic s]ies2 = ! rocks ( ?is gr\p pres5t ess5tially ! same comb9ation ( m9]als z ! dike rocks4 ,9 composition1 ! dike & volcanic rocks are id5tical2 b 9 texture1 z already expla9$1 !re is a va/ diff]5ce4 ,! volcanic rocks diff] s widely 9 texture f bo? ! dike & /ratifi$ species1 t !re is r>ely any difficulty 9 di/+ui%+ !m2 & h5ce !y h 9 e in/ance di/9ct names4 ,volcanic rocks are r>ely f\nd 9 ?is "p ( ! _w2 & specim5s ( mo/ ( !m are difficult to obta94 ,= ?is reason !y c only be notic$ briefly "h1 s9ce x is ! plan ( ?is ,guide to give especial att5tion only to ^? portions ( ! subject :i* c be illu/rat$ by mat]ial )9 easy rea* ( tea*]s4 ,rhyolite4--,?is rock corresponds 9 composition ) granite & gneiss1 b is less frequ5tly micace\s4 ,! or?oclase 9 rhyolite1 & g5]ally 9 volcanic rocks1 is ! cle>1 pellucid v>iety--sanid9e4 ,x is m difficult to sep>ate f qu>tz ?an ord9>y or?oclase1 ! *ief di/+ui%+ feature be+ its cleavage4 ,plagioclase & hornbl5de are common1 b n abundant1 con/itu5ts4 ,! mica1 :5 pres5t1 is usually biotite4 ,! texture ( rhyolite is (t5 m or less di/9ctly porphyritic1 hav+ a f9ely cry/all9e or granul> matrix1 ) int]sp]s$ cry/als ( sanid9e & qu>tz4 ,! rock has usually a r\gh1 h>% feel2 & :ile ! co>s] v>ieties h ! aspect ( granite1 ! f9] approa* petrosilex2 b all are some:at por\s1 :i* is se5 9 ! l[] specific gravity ( rhyolite z comp>$ ) granite & gneiss4 ,tra*yte4--,9 texture & g5]al aspect rhyolite & tra*yte are ne>ly id5tical4 ,tra*yte1 h[ev]1 is d>k]1 conta9s little or no qu>tz1 & m hornbl5de & plagioclase4 ,9 fact1 x agrees 9 composition ) sy5ite4 ,?is is "o ( ! mo/ important ( ! volcanic rocks4 ,obsidian4--,obsidian is %>ply di/+ui%$ f all o!r rocks by its p]fect vitre\s texture2 x is a true volcanic glass4 ,its surface 7specim5 #dg7 is smoo? & glassy1 & its fracture em95tly con*oidal4 ,to ! nak$ eye1 & usually "u ! microscope1 ! typical v>iety is p]fectly homog5e\s2 *emical analysis1 h[ev]1 %[s t x has ! composition1 commonly ( rhyolite1 b sometimes ( tra*yte4 ,obsidian is1 9 fact1 simply rhyolite or tra*yte :i*1 cool+ quickly1 has n _h "t to cry/allize1 b has rema9$ p]man5tly 9 ! amorph\s or glassy /ate4 ,! composition is sometimes p>tially reveal$ :]e a portion ( ! sanid9e comes out 9 di/9ct cry/als porphyritically int]sp]s$ ?r\gh ! glass4 ,! homog5eity ( ! texture is sometimes di/urb$3 by num]\s m9ute conc5tric cracks1 =m+ :at is kn[n z p]litic /ructure & ! v>iety p]lite2 by num]\s small sph]ical concretions1 =m+ ! sph]ulitic /ructure & ! v>iety sph]ulite2 & also by ! b&+1 :i* is ! result ( fl[+ :ile 9 a pla/ic /ate1 :]eby portions ( ! glass ( slightly diff]5t colors are drawn out into lay]s & int]lam9at$4 ,! b&s are r>ely cont9u\s = any di/ance1 be+ usually m]ely elongat$ l5ticul> /reaks4 ,! glassy /ate is g5]ally "o ( inf]ior d5sity1 & h5ce we f9d t obsidian is light] ?an ! cry/all9e rocks ( ! same composition4 ,obsidian is a good illu/ration ( a non-ess5tial color1 = its capacity & jet-black color are due entirely to impurities4 ,9 v ?9 flakes x is transp>5t & :ite4 ,x also =ms a :ite p[d] :5 cru%$1 i4e41 x has a :ite /reak4 ,obsidian is (t5 vesicul>1 f ! expansion ( ! /eam & o!r gases :i* x conta9$ :5 liquid4 ,! mo/ ?or\ghly vesicul> v>ieties are kn[n z pumice 7specim5 #dh74 ,! vesicul> texture1 by r5d]+ ! rock imp]vi\s to light1 conceals ! impurities1 & ?us we get a sn[-:ite pumice f black obsidian4 ,! vesicles are frequ5tly elongat$1 sometimes 9 a def9ite direction1 ?\gh (t5 =m+ an irregul> net-"w ( glassy fibres4 ,pumice is (t5 light en\gh to float on wat]1 & x is transport$ ?\s&s ( miles by ! oceanic curr5ts4 ,x is employ$ 9 ! arts1 & good specim5s c be obta9$ at almo/ any drug-/ore4 ,petrosilex & ,felsite4--,%>ply def9$ gr\ps are unkn[n 9 li?ology1 b all is gradation2 & betwe5 rhyolite & tra*yte1 :i* are always m or less di/9ctly cry/all9e1 & obsidian1 :i* is a true glass & p]fectly amorph\s1 !re is no break4 ,x is impossible to draw a %>p l9e & say1 ,"h ! vitre\s texture ends & ! cry/all9e beg9s2 = ! transition is n abrupt1 b gradual4 ,we recognize1 really1 9 ^! feldspa?ic rocks1 an int]m$iate /ate1 :i* is nei!r cry/all9e nor colloid1 b bo?2 & ?is li?ologi/s h designat$ ! felsitic texture4 ,felsitic matt] _c1 ev5 ) ! highe/ p[]s ( ! microscope1 be resolv$ into sep>ate gra9s or p>ticles2 & x does n exhibit1 except p]haps v indi/9ctly1 ! ph5om5on ( d\ble refraction4 ,9 o!r words1 x is n truly cry/all9e or /ony1 & yet x is j z cle>ly n amorph\s or glassy4 ,feldspa?ic rocks exhibit+ ! felsitic texture 9 :ole or 9 "p are kn[n z felsites4 ,_m high au?orities hold t true felsites are f\nd only among ! eruptive rocks2 :ile o!rs claim t !y are 9 "p1 or :olly1 ( s$im5t>y orig94 ,! writ] accepts ! =m] view4 ,! felsites are 9 "p acid lavas :i* h cool$ too sl[ly to =m a true glass1 l obsidian1 & yet too quickly to become truly cry/all9e1 l rhyolite & tra*yte4 ,b !y are also 9 l>ge "p simply devitrifi$ obsidian4 ,glass is an un/able =m ( m9]al matt]2 & e species ( glass1 includ+ obsidian1 t5ds ) ! lapse ( "t to become cry/all9e or /ony1 ! amorph\s *ang+ to ! felsitic /ructure4 ,?us1 9 _m cases or usually1 :at we n[ call felsites 7 orig9ally true glassy obsidian4 ,be+ p]fectly intimate mixtures ( ! compon5t m9]als1 ! composition ( felsites c usually be det]m9$ ) c]ta9ty only by means ( *emical analysis4 ,by ?is means *iefly1 x has be5 prov$ t !re are felsites agree+ 9 composition ) bo? rhyolite & tra*yte4 ,!re is ?is g5]al diff]5ce 9 composition1 h[ev]1 betwe5 ^! cry/all9e rocks & ! felsites2 viz43 mica1 hornbl5de1 & augite are g5]ally want+ 9 ! latt]4 ,f ?is x foll[s t ! felsites are1 ) unimportant exceptions1 compos$ ei!r ( qu>tz & feldsp> or ( feldsp> alone4 ,! physical diff]5ces betwe5 ! felsites ( unlike composition are n great2 b !y are suffici5t to w>rant ! division ( ! felsites into two species3 a basic species1 to :i* ! t]m felsites may prop]ly be re/rict$2 & an acidic species1 = :i* petrosilex is a v appropriate "n4 ,accord+ to ?is arrangem5t1 felsite is compos$ *iefly ( or?oclase1 &1 z ! table %[s1 agrees 9 composition ) tra*yte2 :ile petrosilex consi/s ma9ly ( or?oclase & qu>tz1 agree+ 9 composition ) rhyolite4 ,we f9d "h no?+ new 9 composition2 b petrosilex & felsite are simply ! cry/all9e rocks :i* we h already /udi$1 repeat$ "u a diff]5t texture4 ,! typical felsite or petrosilex is compos$ entirely ( felsitic matt]1 & is p]fectly homog5e\s1 l fl9t or jasp]1 :i* x closely resembles 9 h>dness & o!r physical *>act]i/ics4 ,z a rule1 h[ev]1 ! rock is n entirely homog5e\s1 b !re is a manife/ t5d5cy 9 ! compon5t m9]als1 & especially 9 ! feldsp>1 to sep>ate out1 usually 9 ! =m ( cry/als4 ,9 ! b&$ v>iety 7specim5 #db7 ! rock is built up ( ?9 lay]s1 :i* are (t5 alt]nately qu>tzose & feldspa?ic4 ,!re is n a p]fect sep>ation ( ! m9]als2 b t ! qu>tz is *iefly 9 ! d>k lay]s1 & ! feldsp> 9 ! light1 is %[n by ! way 9 :i* ! lay]s are affect$ by ! wea!r4 ,"o ( ! mo/ common v>ieties is :]e a portion1 frequ5tly a l>ge portion1 ( ! feldsp> comes out 9 ! =m ( di/9ct1 sep>ate cry/als1 produc+ a porphyritic texture4 ,specim5s #e1 #f1 & #g are examples ( porphyritic felsite2 & aft] exam9+ ^! we c no long] d\bt t feldsp> is an important con/itu5t ( ! rock4 ,petrosilex & felsite are m g5]ally porphyritic ?an any o!r rocks2 & !y are commonly call$ porphyry4 ,x is bett]1 h[ev]1 s9ce almo/ any rock may be porphyritic1 & s9ce ?is texture _c be correlat$ ) any p>ticul> composition1 n to use porphyry z a rock-"n1 b simply z ! "n ( a v important rock-texture4 ,! b&$ & porphyritic textures are ab\t equally *>act]i/ic ( petrosilex & felsite4 ,9 petrosilex1 qu>tz1 z well z feldsp>1 is sometimes porphyritically develop$1 =m+ ! v>iety kn[n z qu>tz-porphyry4 ,!re is no limit to ! proportion ( ! qu>tz & feldsp> :i* may cry/allize out 9 ?is way1 & ?us we f9d a p]fectly gradual passage f normal petrosilex or felsite to ?or\ghly cry/all9e granite & sy5ite4 ,&esite4--,?is rock has ne>ly ! texture ( rhyolite & tra*yte1 b is d>k] & heavi]1 & corresponds 9 composition to diorite1 consi/+ ( plagioclase & hornbl5de1 ) usually m or less sanid9e1 qu>tz1 augite1 biotite1 & magnetite4 ,basalt4--,! rock be>+ ?is famili> "n repres5ts diabase among ! dike rocks4 ,x is ! mo/ basic ( ! volcanic rocks1 & consi/s ( ! m basic v>ieties ( plagioclase1 especially labradorite1 ) augite1 magnetite1 & titanic iron4 ,oliv9e is a v common & *>act]i/ic con/itu5t1 & ! plagioclase is (t5 replac$ 9 "p by leucite & nephelite4 ,! basalts are usually black1 & ( high specific gravity2 & v>y 9 texture f compact to co>sely cry/all9e4 ,! contraction due to cool+ frequ5tly results 9 ! developm5t ( a column> /ructure ( rem>kable regul>ity1 ! columns be+ normally hexagonal & /&+ p]p5dicul>ly to ! cool+ surfaces ( ! mass4 ,?is /ructure occurs 9 o!r eruptive rocks1 b is mo/ *>act]i/ic ( basalt4 ,ta*ylite4--,ta*ylite is a highly basic volcanic glass1 /&+ 9 ! same relation to basalt & &esite t obsidian does to tra*yte & rhyolite4 ,x is mu* heavi] ?an obsidian1 & is p]fectly black & opaque1 except 9 ! f9e/ fibres4 ,x is a comp>atively r>e rock1 = ! reason t basalt & &esite cry/allize m readily ?an ! acidic rocks on pass+ f ! liquid to ! solid /ate4 ,on ! surface ( ! basic lava1 h[ev]1 :]e x is 9 contact ) ! air1 & congeals almo/ in/antly1 a film ( glass is =m$2 b ?is may n be m ?an a small fraction ( an in* 9 ?ickness4 ,l obsidian1 ta*ylite is (t5 vesicul>2 b ! vesicul> basic rocks1 z well z ! solid1 are usually /ony4 ,!y occur 9 va/ abundance 9 _m volcanic regions1 & may be consid]$ ! typical lava 7specim5 #di74 ,9 ! m anci5t lavas1 ! vesicles are frequ5tly fill$ by v>i\s m9]als--*lorite1 epidote1 qu>tz1 calcite1 etc4--deposit$ by infiltrat+ wat]s1 & d]iv$ 9 mo/ cases f ! decomposition ( ! orig9al con/itu5ts ( ! rock4 ,?us ! vesicul> is *ang$ to ! amygdaloidal texture1 & ! lava becomes an amygdaloid 7specim5 #ej74 ,! amygdaloidal texture is common 9 ! basic lavas & r>e 9 pumice1 simply because ! =m] are m readily decompos$ & conta9 a great] v>iety ( bases f :i* second>y m9]als c be =m$4 ,porphyrite & ,melaphyr4--,^! two rocks hold ess5tially ! same relation z reg>ds orig9 & /ructure to ! basic lavas t petrosilex & felsite d to ! acidic lavas4 ,porphyrite agrees 9 composition ) &esite1 & melaphyr ) basalt4 ,!y are usually d>k-color$ rocks hav+ a compact or felsitic texture4 ,porphyrite is1 z ! "n implies1 v commonly porphyritic2 :ile melaphyr is (t5 vesicul> or brecciat$1 exhibit+ all ! /ructural features ( ta*ylite & basalt1 & be+ 9 its old] =ms v g5]ally amygdaloidal4 ,volcanic ,tuff & ,agglom]ate4--,besides ! cry/all9e1 glassy1 & felsitic lavas1 already describ$1 & due *iefly to ! rate ( cool+ ( ! liquid rock1 we may recognize a f\r? class to include ! v abundant lavas :i*1 dur+ explosive eruptions1 are eject$ 9 ! solid /ate1 be+ viol5tly bl[n out ( ! crat] 9 ! =m ( du/ & fragm5ts4 ,fall+ on ! slopes ( ! volcano or ov] ! surr\nd+ c\ntry1 z 9 ! case ( ! buri$ city ( ,pompeii1 ! fragm5tal lavas rema9 l>gely un/ratifi$4 ,b :51 z frequ5tly happ5s1 !y fall into ! sea1 !y are assort$ by ! waves & curr5ts & arrang$ 9 lay]s aft] ! mann] ( ord9>y s$im5ts1 ) :i* !y are (t5 m or less mix$4 ,be=e !y become consolidat$ ! f9] fragm5tal lava1 ( :atev] composition1 is call$ volcanic du/1 & ! co>s] lapilli or volcanic s&2 :ile ! consolidat$ mat]ials are kn[n z tuff & agglom]ate respectively4 ---------------------------------------- -------------------------------- ,,supplem5t ,,to ,,li?ology4 ,illu/ration ,,ve9 ,,rocks4 ,all rocks are n embrac$ 9 ! s$im5t>y & eruptive divisions1 b !re is a ?ird gr& division1 :i*1 al?\gh r>ely m5tion$ or recogniz$ 9 ! m compreh5sive works on geology1 x is deem$ be/ n to leave entirely unnotic$ "h4 ,^! are ! ve9 rocks4 ,!y pres5t an imm5se numb] ( v>ieties1 & yet1 tak5 altoge!r1 =m b a small fraction ( ! e>?'s cru/4 ,!y are1 h[ev]1 ! great repositories ( ! preci\s & o!r metals1 & h5ce are objects ( f> great] int]e/ to ! m9] & practical man ?an ! eruptive rocks1 or1 9 "s p>ts ( ! _w1 ev5 ?an ! s$im5t>y rocks4 ,! ve9 rocks1 l ! eruptive rocks1 occupy fissures 9 ! e>?'s cru/ int]sect+ ! /ratifi$ =mations2 b ! fissures fill$ ) ve9 rocks are call$ ve9s1 & n dikes4 ,we w fir/ notice ! mode ( =mation ( a typical ve91 & !n exam9e its cont5ts4 ,geologi/s are agre$ t wat] p5etrates to a v great dep? 9 ! e>?'s cru/4 ,all m9]als are m or less soluble 9 wat]2 & we may consid] ! wat] circulat+ ?r\gh ! rocks1 especially at consid]able dep?s1 z1 9 mo/ cases1 a saturat$ solution ( ! v>i\s m9]als ( :i* !y are compos$4 ,v slight *anges 9 ! conditions w cause saturat$ solutions to deposit "p ( _! m9]al load4 ,! wat] at great dep?s has a high temp]ature1 & is subject$ to an enorm\s pressure2 & bo? ( ^! circum/ances favor solution4 ,suppose1 n[1 t ^! hot subt]ranean wat]s ent] a fissure 9 ! cru/ & fl[ upw>ds1 p]haps issu+ on ! surface z a w>m m9]al spr+2 z !y approa* ! surface1 ! temp]ature & pressure1 & consequ5tly _! solv5t p[]1 are dim9i%$2 & a portion ( ! dissolv$ m9]als mu/ be deposit$ on ! walls ( ! fissure1 :i* ?us becomes n>r[]1 & 9 ! c\rse ( "t is gradually fill$ up4 ,! ve9 is !n complete2 & ! m9]al wat]s are =c$ to seek a new outlet4 ,ve9s h ! same g5]al =ms z dikes1 s9ce ! fissures are =m$ 9 ! same way = bo?2 b ! ve9 is ( sl[ gr[?1 & may require ages = its completion1 :ile ! dike is =m$ 9 an h\r or a day4 ,x is n[ g5]ally believ$ t wat] is an important ag5t 9 ! =mation ( eruptive rocks2 s9ce !y all conta9 wat] at ! "t ( _! eruption2 & s9ce x has be5 demon/rat$ t1 :ile ord9>y rocks require a temp]ature ( #bjjj to #cjjj = _! fusion 9 ! abs5ce ( wat]1 !y are liquifi$ at temp]atures bel[ #ajjj 9 ! pres5ce ( wat]4 ,9 o!r words1 common rocks are v infusible & insoluble bodies1 & heat & wat] act+ indep5d5tly h little effect ^u !m2 b :5 fire & wat] are comb9$ 9 :at is n[ kn[n z aqueo-igne\s fusion1 !y prove v effici5t ag5ts ( liquefaction4 ,if we adopt ^! views1 !n x c be %[n t1 9 orig91 ve9s & dikes diff] 9 degree only1 & are n fundam5tally unlike2 & ! =mation & relations ( ! ?ree great classes ( rocks may be summ>iz$ z foll[s3-- ,! ocean & atmosph]e1 op]at+ on ! e>?'s surface1 h work$ ov] & /ratifi$ ! cru/1 until ! s$im5t>y rocks h n[ an av]age ?ickness v>i\sly e/imat$ at f t5 to ?irty or =ty miles4 ,?is entire ?ickness ( /ratifi$ rocks1 & a consid]able dep? ( ! und]ly+ un/ratifi$ cru/1 mu/ be saturat$ ) wat]2 & all b ! m sup]ficial portions ( ?is wat]-soak$ cru/ mu/ be v hot1 ! temp]ature increas+ /eadily d[nw>ds f ! surface4 ,bo? eruptive & ve9 rocks orig9ate 9 ?is highly heat$1 hydrat$ cru/4 ,eruptive rocks are =m$ :5 ! heat1 aid$ by m or less wat]1 s(t5s ! rocks1 ei!r /ratifi$ or un/ratifi$1 by aqueo-igne\s fusion1 & ! pla/ic mat]ials are =c$ up ?r\gh fissures to or t[>d ! surface4 ,ve9 rocks are =m$ :5 ! wat]1 aid$ by m or less heat1 dissolves ! rocks1 ei!r /ratifi$ or un/ratifi$1 by :at may be call$ igneo-aque\s solution1 & subsequ5tly deposits ! m9]al matt] 91 i4e41 on ! walls (1 fissures lead+ up to or t[>d ! surface4 ,9 ! case ( ! dike rocks1 heat is ! *ief ag5t1 & wat] m]ely an auxili>y2 :ile ) ! ve9 rocks x is j ! rev]se4 ,b betwe5 ! two x is probably impossible to draw any %>p l9e4 ,! wat] circulat+ ?r\gh ! cru/1 & saturat$ ) its v>i\s m9]al con/itu5ts1 has be5 call$ ! 8juice0 ( ! cru/2 & ve9s are =m$ by ! conc5tration ( ?is e>?-juice 9 fissures4 ,"o ( ! mo/ important *>act]i/ics ( ! ve9 rocks1 z a class1 is ! imm5se v>iety :i* !y pres5t2 = ne>ly e kn[n m9]al is embrac$ among _! con/itu5ts2 & ^! are comb9$ 9 all possible ways & proportions1 s t ! numb] ( comb9ations is almo/ endless4 ,! solv5t p[] ( ! subt]ranean wat]s v>ies = diff]5t m9]als2 & appe>s (t5 to be greate/ = ! r>] species4 ,9 o!r words1 !re is a sort ( selective action1 :]eby _m m9]als :i* exi/ 9 /ratifi$ & eruptive rocks1 s ?9ly diffus$ z to entirely escape ! mo/ ref9$ obs]vation1 are conc5trat$ 9 ve9s 9 masses ( s5sible size2 & our li/s ( kn[n m9]als & *emical elem5ts are und\bt$ly mu* long] ?an !y w\ld be if ^! wond]ful /oreh\ses ( f9e m9]als :i* we call ve9s _h nev] be5 explor$4 ,z a rule1 ! m9]als 9 ve9s =m l>g] & m p]fect cry/als ?an we f9d 9 ei!r ( ! o!r great classes ( rocks4 ,?is is simply because ! conditions are m favorable = cry/allization 9 ve9s ?an 9 dikes or s$im5t>y /rata4 ,9 bo? dike & /ratifi$ rocks1 ! gr[+ cry/als are surr\nd$ on all sides by solid or semi-solid matt]2 &1 be+ ?us hamp]$1 x is simply impossible t !y %\ld become ei!r l>ge or p]fect4 ,9 ! ve91 on ! o!r h&1 !re are usually no su* ob/acles to be ov]come2 b ! cry/als1 />t+ f ! walls ( ! fissure1 gr[ t[>d its c5tre1 _! gr[+ ends project+ into a free space1 :]e !y h fre$om to develop _! normal =ms & to atta9 a size limit$ only1 9 _m cases1 by ! bread? ( ! fissure4 ,)1 possibly1 "s r>e exceptions1 all ! l>ge & p]fect cry/als ( qu>tz1 feldsp>1 mica1 b]yl1 apatite1 fluorite1 & ( m9]als g5]ally1 :i* we see 9 m9]alogical cab9ets1 h orig9at$ 9 ve9s4 ,^? fissures :i* become ! seats ( m9]al ve9s are really ,nature's laboratories = ! production ( r>e & beautiful m9]al specim5s2 & h5ce ! ve9 rocks are ! *ief resort ( ! m9]alogi/1 to :om !y are ( f> great] int]e/ ?an all ! eruptive & /ratifi$ rocks comb9$4 ,! lead+ *>act]i/ics1 !n1 ( ! ve9 rocks may be summ>iz$ z foll[s3 7#a7 ,!y conta9 ne>ly all kn[n m9]als1 includ+ _m r>e species & elem5ts :i* are unkn[n outside ( ?is class ( rocks4 7#b7 ,^! m9]al con/itu5ts1 occurr+ s+ly & comb9$1 give rise to a numb] ( v>ieties ( rocks s va/ z to baffle detail$ description4 7#c7 ,!y exce$ all o!r rocks 9 ! co>s5ess ( _! cry/allization1 & 9 ! p]fection & beauty ( ! s+le cry/als :i* !y af=d4 ,,petrology4 ,9 li?ology we inve/igate ! nature ( ! mat]ials compos+ ! e>?'s cru/--! v>i\s m9]als & aggregates ( m9]als1 or rocks2 :ile 9 petrology we consid] ! =ms & modes ( arrangem5t ( ! rock-masses1--9 o!r words1 ! ar*itecture ( ! e>?4 ,petrology is ! complem5t ( li?ology1 & 9 _m respects x is ! mo/ fasc9at+ division ( geology1 s9ce 9 no o!r direction 9 ?is sci5ce are we br\ght con/antly into su* intimate relations ) ! beautiful & sublime 9 nature4 ,! /ructures ( rocks are ! basis ( ne>ly all natural sc5]y2 = :at we call sc5]y is usually m]ely ! ext]nal expression1 z develop$ by ! p[]ful b delicate sculpture ( ! ag5ts ( erosion--ra9 & fro/1 riv]s & glaci]s1 etc4--( ! geological /ructure ( ! c\ntry4 ,& to ! practis$ eye ( ! geologi/1 a f9e l&scape is n simply a pleasantly or gr&ly div]sifi$ surface1 b x has dep?2 = he reads 9 ! sup]ficial l9eam5ts ! /ructure ( ! rocks out ( :i* !y are c>v$4 ,b1 :ile ! magnitude ( ! ph5om5a adds greatly to ! *>m ( ! /udy1 x also increases ! difficulties & taxes ! +5uity ( ! tea*] ^: "w mu/ be done indoors4 ,accord+ to our ideal me?od1 natural sci5ce ought to be taught ) natural specim5s2 & yet "h our ma9 reliance mu/ be ^u pictures & diagrams4 ,nature1 h[ev]1 has n be5 :olly unm9dful ( our ne$s2 = %e has work$ (t5 ^u a v small z well z a v l>ge scale2 _m ( ! gr&e/ ph5om5a be+ repeat$ 9 m9iature4 ,?us we obs]ve rock-folds or ar*es miles 9 bread? & =m+ m\nta9 masses1 & ( all sizes f t d[n to ! m9ute/ wr9kle4 ,s ) ve9s1 faults1 etc4 ,& ! wond]ful ?+ is t ^! small examples1 :i* may be br\ght into ! class-room1 are usually1 except 9 size1 exactly l ! l>ge4 ,n[ ! aim ( e tea*] 9 ?is dep>tm5t %\ld be to secure a collection ( ^! natural models4 ,x is n an easy ?+ to d1 except "o has pl5ty ( "t2 = !y c r>ely be pur*as$ ( deal]s1 b mu/ usually come z ! *oice/ fruit ( repeat$ excursions to ! natural l$ges & qu>ries1 ! sea%ore & ! m\nta9s4 ,b = ! difficulty ( gett+ ! specim5s !re is "s comp5sation1 s9ce x may be truly said t = ! collector specim5s obta9$ 9 ?is way h an int]e/1 a value1 & a p[] ( in/ruction beyond :at !y w\ld o!rwise possess4 ,classification ( ,/ructures4 ,! /ructures ( rock divide1 at ! outset1 into two classes3--7#a7 ! orig9al /ructures1 or ^? produc$ at ! same "t & by ! same =ces z ! rocks !mselves1 & :i* are1 !re=e1 peculi> to ! class ( rocks 9 :i* !y occur 7e4g4 /ratification1 ripple-m>ks1 fossils1 etc472 & 7#b7 ! subsequ5t /ructures1 or ^? develop$ 9 rocks subsequ5tly to _! =mation1 & by =ces t act m or less uni=mly ^u all classes ( rocks1 & :i* are1 !re=e1 9 a l>ge degree1 common to all k9ds ( rocks 7e4g4 folds1 faults1 jo9ts1 etc474 ,! orig9al /ructures are conv5i5tly & naturally classifi$ 9 accordance ) ! ?ree great classes ( rocks3 7#a7 /ratifi$ rocks1 7#b7 eruptive rocks1 & 7#c7 ve9 rocks2 :ile ! subsequ5t /ructures1 n be+ peculi> to p>ticul> classes ( rocks1 are prop]ly divid$ into ^? produc$ by 7#a7 ! subt]ranean or igne\s ag5cies1 & 7#b7 ! sup]ficial or aque\s ag5cies4 ,illu/ration3 ,fig4 #a4--,section ?r\gh s$im5t deposit$ by ra9 9 a roadside pool3 a4 surface ( roadway2 b4 lay] ( small pebbles & co>se s&2 c4 f9e s& pass+ into d2 d4 ! f9e/ s& & mud4 ,orig9al ,/ructures ( ,/ratifi$ ,rocks4 ,,/ratification4--,all rocks =m$ by /rew+ mat]ials 9 wat]1 & _! deposition 9 successive1 p>allel1 horizontal lay]s1 are /ratifi$2 & ?is /ructure is _! /ratification4 ,x is ! mo/ important ( all rock /ructures2 & !re is no k9d ( /ructure ! orig9 ( :i* is m fully or c]ta9ly kn[n4 ,! deposition ( s$im5t 9 c>efully assort$ horizontal lay]s is readily br\ght )9 ! compreh5sion ( *ildr5 by simple exp]im5ts ) s& & clay 9 wat]2 & /ill bett] by ! exam9ation ( ! deposits =m$ 9 roadside pools dur+ heavy ra9s 7,fig4 #a71 & by digg+ into bea*es & s&b>s1 :i* e *ild w recognize z =m$ ( mat]ials arrang$ by wat]4 ,great /ress %\ld be laid ^u ! fact t a lake l ,erie or ,*ampla9 is simply a l>ge pool ) sev]al m or less turbid /reams fl[+ into x1 :ile ! s+le /ream fl[+ out is cle>1 ! s$im5t hav+ evid5tly be5 deposit$ 9 ! lake2 & t e lake is1 l ! roadside pool1 be+ gradually fill$ up ) s$im5t>y or /ratifi$ rocks4 ,b ! ocean is a /ill l>g] pool1 receiv+ mud & s& f _m /reams2 & s9ce we "k t no?+ escapes f ! ocean b invisible vapor1 x is pla9 t ! mud & s& & all o!r k9ds ( s$im5t c>ri$ into ! ocean mu/ be deposit$ on its floor1 & *iefly1 z we h se51 on t "p ne>e/ ! l&4 ,! consolidation ( bea*es1 b>s1 & mud-flats is all t is necess>y to conv]t !m into /ratifi$ =mations ( conglom]ate s&/one & slate4 ,let u notice n[1 m p>ticul>ly1 ! causes ( visible /ratification4 ,z we c easily prove by an exp]im5t ) clay 9 a bottle ( wat]1 if ! same k9d ( mat]ial is deposit$ cont9u\sly !re w be no visible /ratification 9 ! deposit4 ,x w be z truly /ratifi$ z any =mation1 b n visibly s2 because !re is no?+ 9 ! nature ( ! mat]ial or ! way 9 :i* x is laid d[n to br+ out di/9ct l9es ( /ratification4 ,cont9u\s & uni=m deposition obta9s v frequ5tly 9 nature1 b r>ely cont9ues long en\gh to p]mit ! =mation ( ?ick b$s or /rata4 ,h5ce1 :ile ! /ratification is almo/ always visible on ! l>ge surfaces ( s&/one1 slate1 etc41 expos$ 9 qu>ries & railway cutt+s1 & may usually be se5 9 ! qu>ri$ blocks1 x is (t5 n app>5t 9 h& specim5s1 :i* may repres5t a s+le homog5e\s lay]4 ,!re is "o important exception1 & t is :]e ! p>ticles1 al?\gh ( ! same k9d1 are flat or elongat$4 ,pebbles ( ^! =ms are common on _m bea*es2 & s9ce !y are necess>ily arrang$ horizontally by ! action ( ! wat]1 !y w1 by _! p>allelism1 make ! /ratification ( ! pudd+-/one visible4 ,! same result is accompli%$ /ill m di/9ctly by ! mica scales1 etc41 9 s&/one & slates1 ! leaves & flatt5$ /ems ( vegetation 9 bitum9\s coal1 & ! flat %ells 9 lime/one4 ,9 all o!r cases1 visible /ratification implies "s *ange 9 ! conditions2 ei!r ! deposition 0 int]rupt$1 or diff]5t k9ds ( mat]ial 7 deposit$ at diff]5t times4 ,! fir/ cause produces planes ( easy splitt+1 or fissility1 especially 9 f9e-gra9$ rocks1 l %ale4 ,?is %aly /ructure or lam9ation-cleavage may be due1 9 "s cases1 to pressure1 b x is commonly und]/ood to mean t ea* ?9 lay] ( clay became p>tially consolidat$ be=e ! next "o 0 deposit$ ^u x1 s t ! two c\ld n p]fectly coh]e4 ,p>allel planes ( easy splitt+ are1 h[ev]1 by !mselves1 ( little value z indications ( /ratification1 s9ce ! lam9ation-cleavage is n easily di/+ui%$ f slaty-cleavage 7ro(+ slate7 & p>allel jo9t+1 /ructures develop$ subsequ5tly to ! deposition ( s$im5ts & q indep5d5t ( ! /ratification4 ,! second cause1 or v>iations 9 ! k9d ( s$im5t1 gives alt]nat+ lay]s diff]+ 9 color1 texture1 or composition1 z is se5 frequ5tly 9 s&/one1 slate1 gneiss1 etc42 & ( all ! indications ( /ratification ^! are ! mo/ important & reliable4 ,illu/ration3 ,fig4 #b4--,section %[+ /rata & lam93 a4 conglom]ate2 b4 s&/one2 c4 %ale2 d4 lime/one4 ,a lay] compos$ ?r\gh\t ( ess5tially ! same k9d ( rock1 z conglom]ate or s&/one1 & %[+ no m>k$ planes ( division1 is usually reg>d$ z "o b$ or /ratum1 al?\gh x may v>y consid]ably 9 texture or color2 :ile ! ?9n] portions compos+ ! /ratum & diff]+ slightly 9 color1 texture1 & composition1 & ! ?9 %eets into :i* %aly rocks split1 are ! lam9 or leaves4 ,9 ,fig4 #b ! /rata are designat$ by lett]s1 & ! f9e l9es & r[s ( dots %[ ! con/itu5t lam91 :ile ! :ole section may be reg>d$ z a small "p ( a great geological =mation4 ,! geological record is writt5 *iefly 9 ! s$im5t>y rocks2 & ! =mations1 /rata1 & lam9 may be reg>d$ z ! volumes1 *apt]s1 & pages 9 ! hi/ory ( ! e>?4 ,n[ e feature ( a rock1 li?ological or petrological1 f9ds its highe/ int]e/ 9 ! light :i* x ?r[s ^u ! hi/ory ( ! rock1 i4e41 ^u ! conditions ( its =mation4 ,obs]ve :at ! section 9 ,fig4 #b tea*es conc]n+ ! geological hi/ory ( t locality2 premis+ t any *apt] ( geological hi/ory writt5 9 ! /ratifi$ rocks %\ld be read f ! bottom upw>ds1 s9ce ! l[e/ /rata mu/ h be5 =m$ fir/ & ! highe/ la/4 ,! l[e/ /ratum expos$ is conglom]ate1 indicat+ a %+le bea* swept by /rong curr5ts :i* c>ri$ away ! f9] mat]ial4 ,upw>ds1 ! conglom]ate becomes f9] & %ades (f into s&/one1 & f9ally into %ale1 %[+ t ! wat] has become gradually deep] & m tranquil1 ! %ore hav+1 9 consequ5ce ( ! subsid5ce1 advanc$ t[>d ! l&4 ,! next two /rata %[ t ?is movem5t is probably rev]s$2 at any rate1 ! curr5ts become /rong] aga91 & ! %ale passes gradually into s&/one & conglom]ate4 ,! bea* condition prevails n[ = a long "t1 & ?ick b$s ( s& & gravel are =m$4 ,! sea !n deep5s aga91 & we obs]ve a ?ird passage f co>se to f9e s$im5t4 ,?is locality is n[ remote f ! %ore1 ! g5tle curr5ts br++ only ! f9e/ mud1 :i* sl[ly builds up ! ?ick b$ ( %ale1 9 ! upp] "p ( :i* %ells are abundant1 indicat+ t ! deposition ( me*anical s$im5t has almo/ ceas$1 & t ! %ale is *ang+ to lime/one4 ,! purity ( ! lime/one1 & ! cr9oids & o!r m>9e organisms :i* x conta9s1 prove t ?is has n[ become ! deep1 cle> sea2 & ?is condition is ma9ta9$ = a long p]iod1 = ! lime/one is v ?ick1 & ?is rock is =m$ ) extreme sl[ness4 ,! mo/ important po9t to be ga9$ "h is t e l9e ( /ratification & e *ange 9 ! "* ( ! s$im5ts is due to "s *ange ( correspond+ magnitude 9 ! conditions "u :i* ! rock 0 =m$4 ,! slight & local *anges 9 ! conditions occur frequ5tly & m>k (f ! individual lam9 & /rata1 :ile ! m important & wide-spread *anges det]m9e ! b\nd>ies ( ! gr\ps ( /rata & ! =mations4 ,/rata are subject to con/ant lat]al *anges 9 texture & composition1 i4e41 a b$ or =mation r>ely holds ! same li?ological *>act]i/ics ov] an ext5d$ area4 ,!re are "s /rik+ exceptions1 especially among ! f9]-gra9$ rocks1 l slate1 lime/one1 & coal1 :i* h be5 deposit$ "u uni=m conditions ov] wide areas4 ,x is ! g5]al rule1 h[ev]1 p>ticul>ly ) ! co>se-gra9$ rocks1 :i* h be5 deposit$ 9 %all[ wat] ne> ! l&1 t ! same cont9u\s /ratum und]goes great *anges 9 ?ickness & li?ological "* :5 foll[$ horizontally4 ,a /ratum ( conglom]ate becomes f9] gra9$ & gradually *anges into s&/one1 :i* %ades (f imp]ceptibly into slate1 & slate into lime/one1 etc4 ,:]e ! /ratum is conglom]ate1 its ?ickness w usually be mu* great] & m v>iable ?an :]e x is compos$ ( ! f9] s$im5ts4 ,! rapidity ( ^! *anges 9 c]ta9 cases is well %[n by ! p>allel sections 9 ,fig4 #c4 ,^! repres5t precisely ! same b$s1 z ! connect+ l9es indicate1 at po9ts only tw5ty feet ap>t4 ,illu/ration3 ,fig4 #c4--,p>allel sections %[+ rapid lat]al *anges 9 /rata3 c4 clay2 s4 s&2 ss4 s&/one2 l4 lignite2 f4 fireclay4 ,:5 we glance at ! conditions "u :i* /ratifi$ rocks are n[ be+ =m$1 x is pla9 t all /rata mu/ t]m9ate at ! m>g9 ( ! sea 9 :i* !y 7 deposit$1 & 9 ! m>g9al portions ( t sea1 especially1 mu/ exhibit frequ5t & rapid *anges 9 composition1 etc4 ,! s$im5ts =m+ ! surface ( ! sea-bottom at ! pres5t "t may be reg>d$ z belong+ to "o cont9u\s /ratum2 & x is in/ructive to exam9e a *>t ( any "p ( our coa/1 su* z ,massa*usetts ,bay1 on :i* ! nature ( ! bottom is indicat$ = ea* s\nd+1 & obs]ve ! di/ribution ( ! diff]5t k9ds ( s$im5t4 ,on an irregul> coa/ l ?is1 especially1 ! gravel1 s&1 & mud ( diff]5t colors & textures1 & ! diff]5t k9ds ( %elly bottom1 =m a pat*work1 ! pat*es be+1 = ! mo/ "p1 ( limit$ ext5t & %ad+ (f gradually into ea* o!r4 ,on a m regul> coa/1 l t ( ,new ,j]sey1 ! s$im5ts are di/ribut$ ) correspond+ uni=mity1 ! *anges are less frequ5t & m gradual1 & we h "h a bett] *ance to obs]ve ! normal arrangem5t ( ! s$im5ts along a l9e f ! %ore seaw>ds--gravel1 s&1 mud1 & %ells4 ,on ! bea* we f9d ! %+le & co>se pebbles1 %ad+ (f rapidly into f9e pebbles & s&4 ,! zone or belt ( s&y bottom may v>y 9 wid? f a mile or two to tw5ty miles or m1 becom+ gradually f9] & *ang+ into clay or mud1 :i* cov]s1 usually1 a mu* broad] zone1 sometimes ext5d+ into ! deep] p>ts ( ! sea1 b gradually giv+ way to calc>e\s s$im5ts4 ,h5ce we may say t ! f9] ! s$im5t ! great] ! area ov] :i* x is spread2 b1 on ! o!r h&1 ! co>s] ! s$im5t ! m rapidly x increases 9 ?ickness4 ,9 o!r words1 ! horizontal ext5t ( a =mation deposit$ 9 any giv5 p]iod ( "t is inv]sely1 & ! v]tical ext5t or ?ickness is directly1 proportional to ! size ( ! p>ticles4 ,obs]vations made 9 deep wells & m9es1 & :]e1 by upturn+ & erosion1 ! edges ( ! /rata are expos$ on ! surface1 %[ t ! v]tical ord] ( ! diff]5t k9ds ( s$im5t>y rocks 9 ! e>?'s cru/ is extremely v>iable4 ,b :5 we take a g5]al view ( a great =mation1 x is (t5 app>5t t x consi/s *iefly ( co>se-gra9$ rocks 9 ! l[] "p & f9e-gra9$ rocks 9 ! upp] "p4 ,?is is1 9 g5]al1 a necess>y consequ5ce ( ! fact t a great ?ickness ( s$im5ts c only be =m$ on a subsid+ sea-floor4 ,su* a =mation mu/ consi/ *iefly ( %ore deposits1 & be deposit$ ne> ! %ore :]e ! sea is %all[4 ,h5ce1 #aj1jjj feet ( s$im5ts implies ne>ly t am\nt ( subsid5ce4 ,9 consequ5ce1 ! %ore l9e & ! sev]al zones ( s$im5t advance t[>ds ! l&2 & s& is deposit$ :]e gravel 0 at fir/1 & z ! subsid5ce cont9ues1 bo? clay & lime/one are f9ally deposit$ ov] ! orig9al bea*4 ,:5 ! sea-floor rises1 ! ord] ( ! s$im5ts is rev]s$2 & x w be obs]v$ t 9 consequ5ce ( ! advance & retreat ( ! %ore-l9e1 ! =mations gr[ edgewise to a consid]able ext5t4 ,illu/ration3 ,fig4 #d4--,ov]lap & uncon=mability4 ,,ov]lap ,,& ,,int]position ,,( ,,/rata4--,ano!r consequ5ce ( ! con/ant oscillation ( ! %orel9e is t successive deposits 9 ! same sea w (t5 cov] diff]5t & unequal areas4 ,:51 9 consequ5ce ( subsid5ce1 "o =mation ext5ds beyond & cov]s ! edge ( ano!r1 z %[n 9 ,fig4 #d1 we h ! ph5om5on describ$ z ov]lap4 ,int]position is simil>1 be+ ! case :]e a =mation 7,fig4 #e1 c47 does n1 9 c]ta9 directions1 cov] s wide an area z ! /rata 7b4 d47 above & bel[ x1 :i* are ?us sometimes f\nd 9 contact1 al?\gh normally sep>at$ by ! entire ?ickness ( ! int]m$iate &1 seem+ly1 int]pos$ /ratum4 ,illu/ration3 ,fig4 #e4--;,int]position ( /rata4 ,,uncon=mability4--,we h already se5 t ! rocks on ! l& are be+ con/antly worn away by ! ag5ts ( erosion2 & x is also a matt] ( common obs]vation t ! /rata ?us expos$ are (t5 n horizontal1 b highly incl9$1 hav+ be5 greatly di/urb$ & crumpl$ dur+ _! elevation4 ,n[1 :5 su* a l&-surface subsides to =m ! sea-bottom1 & new /rata are spread horizontally ov] x1 !y w lie across ! upturn$ & erod$ edges ( ! old] rocks1 & fill ! holl[s worn out ( ! latt]1 z %[n 9 ,fig4 #f2 & ! new =mation is !n said to re/ uncon=mably ^u ! old]4 ,two /rata or =mations are uncon=mable :5 ! old] has suff]$ erosion 7,fig4 #f71 or bo? di/urbance & erosion 7,fig4 #d7 be=e ! deposition ( ! new]4 ,illu/ration3 ,fig4 #f4--,uncon=mability4 ,:5 /rata are con=mable1 ! deposition may be presum$ to h be5 ne>ly or q cont9u\s2 b uncon=mability cle>ly proves a prolong$ int]ruption ( ! deposition dur+ :i* ! elevation1 erosion1 & subsid5ce ( ! sea-bottom took place4 ,! section 9 ,fig4 #g %[s a second uncon=mability1 prov+ t ! sea-bottom has "h be5 lift$ ?ree times to =m dry l&4 ,an uncon=mability may sometimes be cle>ly e/abli%$ :5 ! actual contact ( ! two =mations _c be se51 z :]e ! new =mation is a conglom]ate conta9+ fragm5ts ( ! old]4 ,,irregul>ities ,,( ,,/ratification4--,^! are especially noticeable 9 s&/one & conglom]ate1 :i* h be5 deposit$ *iefly by /rong1 local1 & v>iable curr5ts2 ! k9d & quantity ( s$im5t1 ( c\rse1 v>y+ ) ! /r5g? & direction ( ! curr5t4 ,two k9ds ( irregul>ity only may be specially notic$ "h3 7#a7 contemporane\s erosion & deposit1 :]e1 9 consequ5ce ( a *ange 9 ! curr5ts1 f9e mat]ial rec5tly deposit$ is p>tially swept away & its place tak5 by co>s] s$im5ts2 & 7#b7 oblique lam9ation1 or curr5t-b$d+1 :]e ! /rata are horizontal z usual1 b ! compon5t lam9 are incl9$ at v>i\s angles4 ,?is /ructure is *>act]i/ic ( s$im5ts swept along by /rong curr5ts1 especially :5 deposit$ 9 %all[ bas9s or depressions4 ,illu/ration3 ,fig4 #g4--;,d\ble ,uncon=mability3 q4 qu>tzite2 s4 s&/one2 d4 drift4 ,,ripple-,,m>ks4--,all :o h be5 on a bea* or s&-b> mu/ h notic$ ! l9es ( wavy ridges & holl[s1 or ripples1 on ! surface ( ! s&4 ,^! are s&-waves1 produc$ by wat] mov+ ov] ! s&1 or by air mov+ ov] dry s&1 z ord9>y waves are =m$ by air mov+ ov] wat]4 ,ea* tide usually effaces ! ripple-m>ks made by its pr$ecessor & leaves a new s]ies1 to be oblit]at$ by ! next tide4 ,b :]e s$im5t is con/antly accumulat+1 a rippl$ surface may be g5tly ov]spread by a new lay]1 & ?us pres]v$4 ,o!r s]ies ( ripples may1 9 l mann]1 be =m$ & pres]v$ 9 ov]ly+ lay]s2 & :5 ! bea* becomes a firm s&/one1 a section ( x w %[ ! rippl$ surfaces almo/ z di/9ctly z :5 !y 7 fir/ =m$ 7,fig4 #h74 ,ripple-m>ks are mo/ p]fect 9 f9e s&4 ,!y are n =m$ 9 gravel1 because x is too co>se2 nor 9 clay1 because x is too t5aci\s4 ,!y are usually limit$ to %all[ wat]2 & are always reg>d$ z prov+ t ! rocks 9 :i* !y occur are %all[-wat] or bea* deposits4 ,!y are normally at "r angles to ! curr5t t produces !m1 & :]e ?is *anges ) ! direction ( ! w9d1 cross-ripples & o!r irregul>ities are introduc$4 ,ripple-m>ks are also usually p>allel ) ! bea*1 & :5 !y are f\nd 9 ! rocks !y give u ! direction1 z well z ! position1 ( ! anci5t %ore-l9e4 ,aga91 ! friction ( ! wat] pu%es ! s&-gra9s along1 roll+ !m up on "o side ( ! ripple & lett+ !m fall d[n on ! o!r4 ,h5ce ripples1 =m$ by a curr5t are always mov+ & are unsymmetrical on ! cross-section1 pres5t+ a long1 g5tle slope t[>d ! curr5t1 & a %ort1 /eep slope away f x1 ! arr[ 9 ! figure indicat+ ! direction ( ! curr5t1 or ( ! sea 9 ! case ( a bea*4 ,& we may ?us le>n f ! fossil ripples1 9 "s cases1 n only ! position & direction ( ! anci5t %ore1 b also on :i* side ! l& lay1 & on :i* side ! sea4 ,:5 ! wat] is 9 a /ate ( oscillation1 )\t any di/9ct curr5t1 m symmetrical ripples are produc$4 ,illu/ration3 ,fig4 #h4--,ripple-m>ks 9 s&/one4 ,,rill-,,m>ks1 ,,ra9-,,pr9ts1 ,,& ,,sun-,,cracks4--8,"o ( ! mo/ fasc9at+ p>ts ( ! "w ( a field-geologi/ consi/s 9 trac+ ! %ores ( =m] seas & lakes1 & ?us recon/ruct+ ! geography ( successive geological p]iods40 ,8 conclusions1 z we h already se51 are bas$ l>gely ^u ! nature ( ! s$im5ts2 b /ill m conv9c+ is ! evid5ce af=d$ by ^? sup]ficial features ( ! /rata1 :i*1 l ripple-m>ks1 seem1 by !mselves1 q insignificant4 ,& among ^! he lays special emphasis ^u ^? :i* %[ t dur+ _! deposition /rata h at int]vals be5 laid b>e to sun & air4 ,dur+ ebb tide wat] :i* has be5 left at ! upp] edge ( ! bea* runs d[n across ! bea* 9 small rills1 :i* excavate m9iature *annels2 & :5 ^! are pres]v$ 9 ! h>d rocks1 !y prove t ! latt] are bea* deposits1 &1 l ! ripple-m>ks1 %[ ! direction ( ! old %ore4 ,if a heavy %[] ( ra9 falls on a muddy bea* or flat1 ! s$im5t deposit$ by ! return+ tide may cov]1 )\t oblit]at+1 ! small b *>act]i/ic impressions ( ! individual drops2 & ^! m>k+s are frequ5tly f\nd well pres]v$ 9 ! h>de/ slates & s&/ones1 te/ify+ unequivocally to ! conditions "u :i* ! rocks 7 =m$4 ,9 "s cases ! ra9-pr9ts are f\nd to be ridg$ up on "o side only1 9 su* a mann] z to indicate t ! drops z !y fell 7 driv5 aslant by ! w9d4 ,! prom95t side ( ! m>k+1 !re=e1 indicates ! side t[>ds :i* ! w9d blew4 ,muddy s$im5ts1 especially 9 lakes & riv]s1 are (t5 expos$ to ! air & sun dur+ p]iods ( dr\?1 & z !y gradually dry up1 polygonal cracks are =m$4 ,! s$im5t ( ! next lay] w fill ^! sun-cracks2 & :51 z (t5 happ5s1 x is slightly diff]5t f ! dessicat$ lay]1 !y may /ill be trac$4 ,sun-cracks pres]v$ 9 ?is way are v *>act]i/ic ( argillace\s rocks1 &1 ( c\rse1 prove t 9 e>ly times1 z at ! pres5t day1 s$im5ts ( ?is class 7 expos$ by ! tempor>y retreat ( ! wat]4 ,! foot-pr9ts or trails ( l&-animals are (t51 z 9 ! s&/ones & %ales ( ! ,connecticut ,valley1 associat$ )1 & ( c\rse /rongly corroborate1 all ^! o!r evid5ces ( %ore deposits4 ,f ! foot-pr9ts pres]v$ 9 ! rocks we pass naturally to ! consid]ation ( ! fossil rema9s ( plants & animals f\nd entomb$ 9 ! /rata4 ,,fossils4--,al?\gh fossils f9d _! highe/ int]e/ 9 ! light :i* !y ?r[ ^u ! succession ( life on ! globe1 !y may also be prop]ly reg>d$ z /ructural features ( /ratifi$ rocks2 & any "o :o has se5 ! dead %ells1 crabs1 fi%es1 etc41 on ! bea* w readily und]/& h[ fossils get into ! rocks4 ,x is n our prov9ce "h to /udy ! /ructure ( ! fossils !mselves1 = t w\ld involve u 9 a c\rse 9 paleontology1 a task belong+ to ! biologi/ r ?an ! geologi/2 b we w m]ely obs]ve ! ?ree pr9cipal degrees 9 ! pres]vation ( fossils3-- #a4 ,orig9al composition n completely *ang$4--,ext9ct elephants h be5 f\nd froz5 9 ! riv]-bluffs ( ,sib]ia s p]fectly pres]v$ t dogs & wolves ate _! fle%4 ,! bodies ( animals are also f\nd well pres]v$ 9 peat-bogs4 ,all coal is simply fossil vegetation reta9+ 9 a l>ge degree ! orig9al composition2 & ! same is true ( f]ns1 etc41 pres]v$ z black impressions 9 ! rocks4 ,all bones & %ells consi/ ( m9]al matt] :i* makes !m h>d1 & animal matt] :i* makes !m t\gh & /rong4 ,9 v _m cases1 especially 9 ! new] =mations1 ! animal matt] is /ill p>tially1 & ! m9]al matt] almo/ :olly1 intact4 #b4 ,orig9al composition completely *ang$1 b =m & /ructure pres]v$4--,all k9ds ( fossils are commonly call$ petrifactions1 b only ^? pres]v$ 9 ?is second way are truly petrifi$1 i4e41 turn$ to /one4 8,petrifi$ wood is ! be/ illu/ration1 & 9 a good specim5 n only ! ext]nal =m ( ! wood1 n only its g5]al /ructure--b>k1 wood1 radiat+ silv]-gra91 & conc5tric r+s ( gr[?--are disc]nible1 b ev5 ! microscopic cellul> /ructure ( ! wood1 & ! exquisite sculptur+ ( ! cell-walls1 are p]fectly pres]v$1 s t ! k9d ( wood may (t5 be det]m9$ by ! microscope ) ! utmo/ c]ta9ty4 ,yet n "o p>ticle ( ! organic matt] ( ! wood rema9s4 ,x has be5 entirely replac$ by m9]al matt]2 usually by "s =m ( silica4 ,! same is true ( ! %ells & bones ( animals40--,,le ,,conte4 #c4 ,orig9al composition & /ructure bo? oblit]at$1 & =m alone pres]v$4--,?is occurs mo/ commonly ) %ells1 al?\gh fossil trees are also (t5 good illu/rations4 ,! g5]al result is accompli%$ 9 sev]al ways3 7a7 ,! %ell aft] be+ buri$ 9 ! s$im5t may be remov$ by solution1 leav+ a m\ld ( its ext]nal =m1 7b7 ,?is m\ld may subsequ5tly be fill$ by ! infiltration ( f9] s$im5t1 =m+ a ca/ ( ! ext]ior ( ! %ell4 7c7 ,! %ell1 be=e its solution1 may h be5 fill$ ) mud2 & if ! %ell itself is !n dissolv$1 we h a ca/ ( its int]ior 9 a m\ld ( its ext]ior4 ,,"t ,,requir$ ,,= ,,! ,,=mation ,,( ,,/ratifi$ ,,rocks4--,_m attempts h be5 made to det]m9e ! "t requir$ = ! deposition ( any giv5 ?ickness ( /ratifi$ rocks4 ,( c\rse1 only r\ghly approximate results c be hop$ = 9 mo/ cases2 b ^! are at lea/ suffici5t to make x c]ta9 t geological "t is v long4 ,! av]age relative rate ( gr[? ( diff]5t k9ds ( s$im5t is1 h[ev]1 less op5 to d\bt1 = we h already se5 t co>se s$im5ts l gravel & s& accumulate mu* m rapidly ?an f9] s$im5ts l clay & lime/one2 & we are sometimes able to comp>e ^! two classes ( rocks on a v l>ge scale4 ,?us1 dur+ :at is kn[n z ! ,paleozoic era1 a sea ext5d$ f ! ,blue ,ridge to ! ,rocky ,m\nta9s4 ,along ! ea/]n m>g9 ( ?is sea1 :]e ! ,alleghany ,m\nta9s n[ /&1 s$im5ts--*iefly conglom]ate & s&/one1 ) "s slate & less lime/one--accumulat$ to a ?ickness ( ne>ly #dj1jjj feet4 ,t[>d ! we/1 away f ! old %ore-l9e1 ! co>se s$im5ts gradually die out1 & ! =mations become f9] & ?9n]4 ,9 we/]n ,ohio & ,indiana1 slate & lime/one pr$om9ate2 :ile 9 ! c5tral "p ( ! anci5t sea1 9 ,ill9ois & ,miss\ri1 ! paleozoic s$im5ts are almo/ :olly lime/ones1 & h a ?ickness ( only #djjj to #ejjj feet4 ,9 o!r words1 :ile "o foot ( lime/one 0 =m+ 9 ! ,mississippi ,valley1 eight to t5 feet ( co>s] s$im5ts 7 deposit$ 9 ,p5nsylvania4 ,! be/ e/imates %[ t coral-reefs rise--i4e41 lime/ones are =m$ on !m--at ! rate ( ab\t "o foot 9 two hundr$ ye>s4 ,b coral lime/ones gr[ mu* m rapidly ?an lime/ones 9 g5]al4 ,s&/ones sometimes accumulate s rapidly t trees are buri$ be=e !y h "t to decay & fall 7,fig4 #i74 ,su* a buri$ =e/1 l a coal-b$1 repres5ts a l& surface1 & proves a subsid5ce ( ! l&2 & 9 "s cases1 z indicat$ by ! section1 repeat$ oscillations ( ! cru/ may be prov$ 9 ?is way4 ,! mud deposit$ by ! annual ov]fl[ ( ! ,nile is =ty feet ?ick ne> ! anci5t city ( ,memphis2 & ! p$e/al ( ! /atue ( ,rameses ,,ii41 believ$ to h be5 erect$ ,b4,c4 #acfa1 is buri$ to a dep? ( n9e feet1 f\r in*es1 indicat+ t #ac1ejj ye>s h elaps$ s9ce ! ,nile began to spread its mud ov] ! s&s ( ! des]t4 ,illu/ration3 ,fig4 #i4--;,erect fossil trees4 ,b ! greate/ difficulty 9 e/imat+ ! "t requir$ = ! =mation ( any s]ies ( /rata arises f ! fact t we _c usually ev5 guess at ! l5g? ( ! p]iods :5 ! deposition has be5 p>tially or :olly int]rupt$4 ,n[ & !n1 h[ev]1 we f9d evid5ce t ^! p]iods may be v long4 ,a lay] ( fossil %ells 9 s&/one or slate proves an int]ruption ( me*anical deposition4 ,b$s ( coal1 fossil =e/s1 & o!r indications ( l& surfaces are /ill m conclusive4 ,! int]position ( /rata 7,fig4 #e7 proves a prolong$ int]ruption ( deposition ov] ! area n cov]$ by ! int]pos$ b$4 ,b ! mo/ important ( all evid5ce is t af=d$ by uncon=mability2 & ! l5g? ( ! lo/ int]val betwe5 ! two =mations is measur$ approximately by ! erosion ( ! old]4 ,orig9al ,/ructures ( ,eruptive ,rocks4 ,! /ructures ( ?is class are divisible into ^? p]ta9+ to ! volcanic rocks & ^? p]ta9+ to ! fissure or dike rocks4 ,b s9ce volcanoes are r>e 9 ?is "p ( ! _w1 :ile dikes are well develop$ 9 _m sections ( our c\ntry1 x seems be/ to give our att5tion *iefly to ! latt]4 ,illu/ration3 ,fig4 #aj4--,typical dikes4 ,illu/ration3 ,fig4 #aa4--,section ( a granite mass4 ,! t]m dike is a g5]al "n = all masses ( eruptive rocks t h cool$ & solidifi$ 9 fissures or cavities 9 ! e>?'s cru/4 ,b ! "n is commonly re/rict$ to ! m regul>1 wall-l masses 7,fig4 #aj71 ^? hav+ extremely irregul> outl9es1 l mo/ masses ( granite 7,fig4 #aa71 be+ kn[n simply z eruptive masses4 ,! propriety ( ?is di/9ction is app>5t :5 we consid] ! orig9 ( dike z a geological t]m4 ,x 0 fir/ us$ 9 ?is s5se 9 s\!rn ,scotl&1 :]e almo/ any k9d ( a wall or b>ri] is call$ a dike4 ,! dikes trav]se ! diff]5t /ratifi$ =mations l gigantic walls1 :i* are (t5 enc\nt]$ by ! coal-m9]s1 & on ! surface are frequ5tly left 9 relief by ! erosion ( ! s(t] enclos+ rock1 s t 9 ! we/ ( ,scotl&1 especially1 !y are actually made use ( = enclosures4 ,9 o!r cases ! dike has decay$ fa/] ?an ! enclos+ rock1 & its position is m>k$ by a dit*-l depression4 ,! n>r[1 /raight1 & p]p5dicul> clefts or *asms obs]v$ on _m coa/s are usually due to ! removal ( ! wall-l dikes by ! action ( ! waves4 ,dikes are sometimes m]e plates ( rock1 traceable = a few y>ds only2 & !y range 9 size f t up to ^? a hundr$ feet or m 9 wid?1 & traceable = scores ( miles across ! c\ntry1 _! outcrops =m+ prom95t ridges4 ,! sides ( dikes are (t5 z p>allel & /raight ( ^? ( built walls1 ! resemblance to human workman%ip be+ height5$ by ! num]\s jo9ts :i*1 int]sect+ ea* o!r along ! face ( a dike1 rem9d u ( well-fitt$ masonry4 ,,=ms ,,( ,,dikes4--,a dike is ess5tially a ca/+4 ,melt$ rock is =c$ up f ! heat$ int]ior into a cavity or crack 9 ! e>?'s cru/1 cools & solidifies !re1 &1 l a metallic ca/+1 assumes ! =m ( ! fissure or m\ld4 ,9 o!r words1 ! =m ( ! dike is exactly t ( ! fissure into :i* ! lava 0 inject$4 ,n[ ! =ms ( fissures dep5d p>tly ^u ! nature ( ! =ce t produces !m1 b v l>gely ^u ! /ructure--& especially ! jo9t-/ructure--( ! enclos+ rocks4 ,ne>ly all rocks are trav]s$ by planes ( division or cracks call$ jo9ts1 :i* usually run 9 sev]al directions1 divid+ ! rock into blocks4 ,& x is probable t dike-fissures are mo/ commonly produc$1 n by break+ ! rocks anew1 b by wid5+ or op5+ ! pre-exi/+ jo9t-cracks4 ,h5ce ! /raight & regul> jo9t+ ( slate1 lime/one & mo/ s$im5t>y rocks is accompani$ by wall-l dikes--! typical dikes 7,fig4 #aj72 :ile ! m irregul> jo9t+ ( granite & o!r massive rocks gives rise to s9u\s1 bran*+1 v>iable dikes4 ,! g5]al dep5d5ce ( dikes ^u ! jo9t-/ructure ( ! rocks is prov$ by ! facts t dikes1 l jo9ts1 are normally v]tical or highly incl9$1 & t !y are usually p>allel ) ! pr9cipal sy/ems ( jo9ts 9 ! same di/rict4 ,! wall-l dikes also give (f bran*es1 b usually 9 a regul> mann]1 z %[n 9 ,fig4 #ab4 ,illu/ration3 ,fig4 #ab4--;,dike ) regul> bran*es4 ,,/ructure ,,( ,,dikes4--,! rock trav]s$ by a dike is call$ ! c\ntry or wall rock4 ,fragm5ts ( ?is are (t5 torn (f by ! igne\s mat]ial1 & become enclos$ 9 ! latt]4 ,su* enclos$ fragm5ts may sometimes =m ! ma9 "p ( ! dike1 :i* !n1 s9ce !y are necess>ily angul>1 (t5 assumes ! aspect ( a breccia4 ,?is is ! only important exception to ! rule t dikes are homog5e\s 9 composition2 i4e41 9 ! same dike we c usually f9d--f end to end1 f side to side1 & probably f top to bottom--no ess5tial diff]5ce 9 composition4 ,b !re is (t5 a m>k$ contra/ 9 texture betwe5 diff]5t p>ts ( a dike1 & especially betwe5 ! sides & c5tral portion4 ,! liquid rock loses heat mo/ rapidly :]e x is 9 contact ) ! cold walls ( ! fissure1 & solidifies be=e x has "t to cry/allize1 rema9+ compact & sometimes ev5 glassy2 :ile 9 ! middle ( ! dike1 unless x is v n>r[1 x cools s sl[ly z to develop a di/9ctly cry/all9e texture4 ,!re is no abrupt *ange 9 texture1 b a gradual passage f ! compact bord] to ! co>sely cry/all9e or porphyritic middle portion4 ,x is obvi\s t a simil> gradation 9 texture mu/ exi/ betwe5 ! top & bottom ( a dike4 ,,contact ,,ph5om5a4--,"u ?is head are gr\p$ ! int]e/+ & important ph5om5a obs]vable along ! contact betwe5 ! dike & wall-rock4 ,^! ?r[ light ^u ! conditions ( =mation ( dikes1 & are (t5 dep5d$ ^u to %[ :e!r a rock mass is a dike or n4 ,! /ud5t w obs]ve "h3-- #a4 ,! detail$ =m ( ! contact4 ,x may be /raight & simple1 or exce$+ly irregul>1 ! dike p5etrat+ ! wall1 & enclos+ fragm5ts ( x1 z 9 ,fig4 #aa1 :i* is a typically igne\s contact4 #b4 ,! alt]ation ( ! wall-rock by heat4 ,?is may consi/ 93 7a7 coloration1 %ales & s&/ones be+ r$d5$ 9 ! same way z :5 clay is burnt = bricks2 7b7 bak+ & induration1 s&/one be+ conv]t$ into qu>tzite & ev5 jasp]2 clay1 slate1 etc41 be+ n only bak$ to a fl9ty h>dness1 b actually vitrifi$1 z 9 porcela9ite2 & bitum9\s coal be+ conv]t$ into natural coke or an?racite2 & 7c7 cry/allization1 *alk1 & o!r lime/ones be+ *ang$ to m>ble1 & cry/als ( pyrite1 calcite1 qu>tz1 etc41 be+ develop$ 9 slate1 s&/one1 & o!r rocks4 #c4 ,! alt]ation ( ! dike-rock by 7a7 m rapid cool+1 & 7b7 ! access ( !rmal wat]s4 ,! alt]ation ( ! wall-rock may ext5d only a few in*es or _m y>ds f ! dike1 gradually dim9i%+ ) ! di/ance2 & ! cases are surpris+ly num]\s :]e !re is no p]ceptible alt]ation2 &1 aga91 ! alt]ation is usually mutual1 ! dike-rock be+ alt]$ 9 texture1 color1 & composition4 ,illu/ration3 ,fig4 #ac4--;,ideal cross-section ( a laccolite4 ,illu/ration3 ,fig4 #ad4--;,ideal cross-section ( a volcano4 ,,intrusive ,,b$s4--,we commonly ?9k ( dikes z cutt+ across ! /rata1 b !y (t5 lie 9 planes p>allel ) !m2 & ! same dike may run across ! b$s 9 "s p>ts ( its c\rse & betwe5 !m 9 o!rs 7,fig4 #ab71 or ! con=mable dike maybe simply a lat]al bran* ( a ma9 v]tical dike1 z %[n 9 ! same figure4 ,all dikes or portions ( dikes ly+ con=mably betwe5 ! /rata are call$ intrusive b$s or %eets4 ,:5 a dike fails to rea* ! surface1 b spreads out horizontally betwe5 ! /rata1 =m+ a ?ick dome or ov5-%ap$ intrusive b$1 ! latt] is call$ a laccolite 7,fig4 #ac74 ,laccolites are sometimes ( imm5se volume1 conta9+ sev]al cubic miles ( rock4 ,fig4 #ad enables u to comp>e ! laccolite ) ! volcano4 ,9 ! "o case a l>ge m\nd ( eruptive mat]ial accumulates betwe5 ! /rata1 ! ov]ly+ b$s be+ lift$ into a dome2 :ile 9 ! o!r case ! fissure or v5t rea*es ! surface1 & ! m\nd ( lava is built up on top ( ! gr\nd4 ,,cotemporane\s ,,b$s4--,:5 ! lava emitt$ by a crat] is suffici5tly liquid1 x spreads out horizontally1 =m+ a volcanic %eet or b$4 ,if su* an eruption is subm>9e1 or ! lava fl[ is subsequ5tly cov]$ by ! sea1 s$im5t>y deposits are =m$ ov] x2 & b$s ( lava :i* ?us come to lie con=mably betwe5 s$im5t>y /rata are kn[n z cotemporane\s %eets or b$s1 because !y belong1 9 ord] ( "t1 9 ! position 9 :i* we f9d !m1 be+1 l any memb] ( a /ratifi$ s]ies1 new] ?an ! und]ly+ & old] ?an ! ov]ly+ /rata4 ,cotemporane\s lava-fl[s are sometimes repeat$ aga9 & aga9 9 ! same di/rict1 & ?us important =mations are built up ( alt]nat+ igne\s & aque\s deposits4 ,evid5tly1 ! /ud5t :o w\ld read correctly ! record ( igne\s activity 9 ! pa/ mu/ be able to di/+ui% intrusive & cotemporane\s b$s4 ,! pr9cipal po9ts to be consid]$ 9 mak+ ?is di/9ction are3 7#a7 ,! intrusive b$ is ess5tially a dike1 d5se & m or less cry/all9e 9 texture1 alt]+1 & (t5 enclos+ fragm5ts (1 bo? ! und]ly+ & ov]ly+ /rata1 & frequ5tly jogg+ across or p5etrat+ ! s$im5ts4 7#b7 ,! cotemporane\s b$1 on ! o!r h&1 be+ ess5tially a lava-fl[1 is mu* less d5se & cry/all9e1 be+ usually di/9ctly scoriace\s or amygdaloidal1 especially at ! bord]s1 & ! und]ly+ /rata alone %[+ heat action1 or occurr+ z enclosures 9 ! lava2 = ! ov]ly+ /rata are new] ?an ! lava1 & (t5 consi/ l>gely1 at ! base1 ( wat]-worn fragm5ts ( ! lava4 ,,ages ,,( ,,dikes4--,! ages ( dikes may be e/imat$ 9 sev]al ways4 ,!y are necess>ily new] ?an any /ratifi$ =mation :i* !y int]sect or ( :i* !y enclose fragm5ts2 b any =mation cross+ ! top ( a dike mu/ usually be reg>d$ z new] ?an ! dike1 especially if x conta9s wat]-worn fragm5ts ( ! dike rock4 ,! relative ages ( diff]5t dikes are det]m9$ by _! relations to ! /ratifi$ =mations2 & /ill m easily by _! mutual int]sections1 on ! pr9ciple t :5 two dikes cross ea* o!r1 ! int]sect+ mu/ be new] ?an ! int]sect$ dike4 ,x is sometimes possible1 9 ?is way1 to prove sev]al di/9ct p]iods ( eruption 9 ! same limit$ di/rict4 ,! textures ( dikes also (t5 af=d reliable indications ( _! ages2 =1 z we h already se51 ! upp] "p ( a dike1 cool+ rapidly & "u little pressure1 mu/ be less d5se & cry/all9e ?an ! deep-seat$ portion1 :i* cools sl[ly & "u great pressure4 ,n[1 ! l[]1 co>sely cry/all9e "p ( a dike c usually be expos$ on ! surface only z ! result ( enorm\s erosion2 & erosion is a sl[ process1 requir+ va/ p]iods ( "t4 ,h5ce1 :5 we see a co>se-gra9$ dike outcropp+ on ! surface1 we are ju/ifi$ 9 reg>d+ x z v old1 = all ! f9e-gra9$ upp] "p has be5 gradually worn away by ! action ( ! ra91 fro/1 etc4 ,o!r ?+s be+ equal1 co>se-gra9$ mu/ be old] ?an f9e-gra9$ dikes2 & ! texture ( a dike is at once a measure ( its age & ( ! am\nt ( erosion :i* ! region has suff]$ s9ce x 0 =m$4 ,,eruptive ,,masses4--,9 /rik+ contra/ ) ! m or less wall-l dikes are ! highly irregul>1 & ev5 ragg$1 outl9es ( ! eruptive masses2 & x is wor? :ile to notice ! probable cause ( ?is contra/4 ,! true dikes are =m$1 = ! mo/ "p1 ( comp>atively f9e-gra9$ rocks--! typical 8traps02 :ile ! eruptive masses consi/ *iefly ( ! co>se-gra9$ or granitic v>ieties4 ,n[ we h j se5 t ! co>se-gra9$ rocks h be5 =m$ at great dep?s 9 ! e>?'s cru/1 :ile ! f9e-gra9$ are comp>atively sup]ficial4 ,b we h good reason = believ+ t ! jo9t-/ructure1 ^u :i* ! =ms ( dikes s l>gely dep5d1 is n well develop$ at great dep?s1 :]e ! rocks are t\gh5$1 if n s(t5$1 by ! high temp]ature4 ,9 o!r words1 trap dikes are =m$ 9 ! jo9t$ =mations1 :i* break regul>ly2 :ile ! granitic masses are =m$ :]e ! abs5ce ( jo9t-/ructure & a high temp]ature comb9e to cause extremely irregul> rifts & cavities :5 ! cru/ is brok54 ,,volcanic ,,pipes ,,or ,,necks4--,e volcano & e lava-fl[ or volcanic %eet mu/ be connect$ ) ! e>?'s int]ior by a *annel or fissure1 :i* becomes a dike :5 ! lava ceases to fl[4 ,b ! conv]se proposition is n true1 = x is probable t _m dikes did n orig9ally rea* ! surface1 b h be5 expos$ by subsequ5t d5udation4 ,?is is conspicu\sly ! case ) laccolites & o!r =ms ( intrusive %eets4 ,volcanic %eets or b$s h probably (t5 result$ f ! ov]fl[ ( ! lava at all po9ts ( an ext5sive fissure or sy/em ( fissures2 b ! v5t ( ! true volcano mu/ be m circumscrib$1 an approximately circul> op5+ 9 ! e>?'s cru/1 al?\gh d\btless orig9at+ 9 a fissure or at ! int]section ( two or m fissures1 ! lava cont9u+ to fl[ at ! wide/ "p ( ! w\nd 9 ! cru/ long aft] x has congeal$ 9 ! n>r[] p>ts4 ,su* a tube is kn[n z ! neck or pipe ( ! volcano2 & volcanic necks are a highly int]e/+ class ( dikes1 s9ce !y det]m9e ! exact location ( _m an anci5t volcano1 :]e ! volcanic pile itself has long s9ce be5 swept away4 ,necks & dikes are ! d[nw>d prolongations or roots ( ! volcanic cone or %eet1 & _c be expos$ on ! surface until ! volcanic fires h gone out & ! ag5ts ( erosion h remov$ ! great] "p ( ! eject$ mat]ials4 ,h5ce1 equally ) ! dikes :i* orig9ally fail$ to rea* ! surface1 !y1 :]ev] op5 to our obs]vation1 te/ify to ext5sive erosion & a va/ antiquity4 ,orig9al ,/ructures ( ,ve9 ,rocks4 ,_m ?+s call$ ve9s are improp]ly s call$1 su* z dikes ( granite & trap1 & b$s ( coal & iron-ore4 ,! small]1 m irregul>1 bran*+ dikes1 especially1 are v commonly call$ ve9s1 & to di/+ui% ! true ve9s f ^! eruptive masses1 !y are designat$ z m9]al ve9s or lodes1 al?\gh ! t]m lode is usually re/rict$ to ! metallif]\s ve9s4 ,,orig9 ,,( ,,ve9s4--,v>i\s !ories ( ! =mation ( ve9s h be5 propos$1 b ! mo/ ( ^! are ( hi/oric int]e/ m]ely1 = geologi/s are n[ well agre$ t ne>ly all true ve9s h be5 =m$ by ! deposition ( m9]als f solution 9 fissures or cavities 9 ! e>?'s cru/4 ,9 _m cases1 especially :]e ! ve9s are ( limit$ ext5t1 x seems probable t a "p or all ( ! m9]al matt] 0 d]iv$ f ! imm$iately enclos+ rocks1 be+ dissolv$ out by p]colat+ wat]2 & ^! are kn[n z segregation or lat]al secretion ve9s4 ,b x is q c]ta9 t z a g5]al rule ! m9]al solutions h come *iefly f bel[1 ! deep-seat$ !rmal wat]s well+ up ?r\gh any *annel op5$ to !m1 & gradually deposit+ ! dissolv$ m9]als on ! walls ( ! fissure z ! temp]ature & pressure are dim9i%$4 ,?is case1 h[ev]1 diff]s f ! fir/ only 9 d]iv+ ! ve9-=m+ m9]als f m remote & deep] portions ( ! enclos+ rocks2 & ?us we see t ve9-=mation1 :e!r on a l>ge or a small scale1 is always ess5tially a process ( segregation4 ,we "k t e volcano & e lava fl[ mu/ be connect$ bel[ ! surface ) a dike2 & x is almo/ equally c]ta9 t ! wat]s ( m9]al spr+s =m+ tuface\s m9]al deposits on ! surface1 z 9 ! geys] di/ricts1 also deposit a portion ( ! dissolv$ m9]als on ! walls ( ! subt]ranean *annels1 :i* are ?us be+ gradually fill$ up & conv]t$ into m9]al ve9s1 :i* w be expos$ on ! surface :5 erosion has remov$ ! tuface\s ov]fl[4 ,?is connection ( ve9-=mation ) ! sup]ficial deposits ( exi/+ spr+s has be5 cle>ly prov$ 9 sev]al important in/ances 9 ,nevada & ,cali=nia4 ,ve9s occur *iefly 9 old1 metamorphic1 & highly di/urb$ =mations1 :]e !re is abundant evid5ce ( ! =m] exi/5ce ( pr(\nd fissures1 & 9 regions simil> to ^? 9 :i* !rmal spr+s occur to-day4 ,9 ! supplem5t to ! li?ological section ! /ud5t w f9d ! =mation ( a typical ve9 briefly describ$ & contra/$ ) t ( a typical dike2 also a brief acc\nt ( ! li?ological peculi>ities ( ve9 rocks1 & g5]al /atem5ts conc]n+ _! relative abundance & va/ economic importance4 ,,ext]nal ,,*>act]i/ics ,,( ,,ve9s4--,! typical ve9 may be describ$ z a fissure ( indef9ite l5g? & dep?1 fill$ ) m9]al sub/ances deposit$ f solution4 ,ext]nally1 x is v simil> to ! typical dike1 = ! fissures are made 9 ! same way = bo?4 ,ve9s are normally highly incl9$ to ! horizon2 !y exhibit 9 ne>ly e respect ! same g5]al relations to ! /ructure ( ! c\ntry rock z dikes2 & ! ages ( ve9s are det]m9$ 9 ! same way z ! ages ( dikes4 ,! ext5sive m9+ op]ations to :i* ve9s h be5 subject$ 9 all p>ts ( ! _w1 h made our k ( _! =ms bel[ ! surface v full & accurate4 ,x has be5 le>n$ 9 ?is way t v (t5 ! correspond+ portions ( ! walls ( a ve9 d n co9cide 9 position1 b "o side is high] or l[] ?an ! o!r1 %[+ t ! walls slipp$ ov] ea* o!r :5 ! fissure 0 =m$ or subsequ5tly2 & ?is fault+ or displacem5t ( ! walls appe>s to be mu* m common ) ve9s ?an ) dikes1 p]haps because ! fissures rema9$ op5 mu* long]4 ,?is slipp+ ( ! walls is ! pr9cipal cause ( ! almo/ con/ant *anges 9 ! wid? ( ve9s4 ,=1 s9ce ! walls are nev] true planes1 & are (t5 highly irregul> any unequal movem5ts mu/ br+ !m ne>] toge!r at "s po9ts ?an at o!rs4 ,z a rule1 ! enorm\s friction accompany+ ! fault+1 ei!r cru%es ! wall-rock1 or poli%es & /riates x1 produc+ ! highly *>act]i/ic surfaces kn[n z slick5-sides4 ,:]e ! wall is f9ely pulv]iz$ 9 ?is way1 or is p>tially decompos$ be=e or aft] ! fill+ ( ! fissure1 a ?9 lay] ( s(t1 argillace\s mat]ial is =m$1 sep>at+ ! ve9 prop] f ! wall-rock4 ,! m9]s call ?is ! selvage2 & x is a v *>act]i/ic feature ( ! true fissure ve9s4 ,fragm5ts ( ! wall-rock are frequ5tly enclos$ 9 ve9s1 & ! latt] sometimes bran* or divide 9 su* a way z to surr\nd a l>ge mass ( ! wall1 :i* is kn[n z a 8horse40 ,a simil> result is accompli%$ :5 a fissure is re-op5$ aft] be+ fill$1 if ! new fissure does n co9cide exactly ) ! old4 ,x has be5 prov$ t ve9s h ?us be5 re-op5$ & fill$ sev]al times 9 succession2 & 9 ?is way fragm5ts ( ! old] ve9 mat]ial become enclos$ 9 ! new]4 ,al?\gh usually det]m9$ 9 direction by ! jo9t-/ructure ( ! c\ntry rock1 ve9s are (t5 p>allel ) ! b$d+1 especially 9 highly incl9$1 s*i/ose =mations4 ,su* int]b$d$ ve9s are commonly di/9ctly l5ticul> 9 =m1 occupy+ rifts 9 ! /rata :i* ?9 out 9 all directions & are (t5 v limit$ 9 ext5t4 ,:e!r con=m+ ) ! jo9t-/ructure or b$d+1 ve9s are commonly arrang$ 9 sy/ems by _! p>allelism1 ^? ( diff]5t sy/ems or directions usually diff]+ 9 age & composition1 & ! old] ve9s be+ g5]ally fault$ or displac$ :5 int]sect$ by ! new]4 ,,int]nal ,,*>act]i/ics ,,( ,,ve9s4--,int]nally1 ve9s & dikes are /rongly contra/$2 & x is ^u ! int]nal features1 *iefly1 z previ\sly expla9$1 t we mu/ dep5d = _! di/9ction4 ,9 metallif]\s ve9s ! m9]als conta9+ ! metal s\ght = 7! gal5ite1 sphal]ite1 etc47 are ! ore2 :ile ! non-metallif]\s m9]als 7! qu>tz1 feldsp>1 calcite1 etc47 are call$ ! gangue or ve9-/one prop]4 ,al?\gh ! comb9ations ( m9]als 9 ve9s are almo/ endless1 yet c]ta9 associations ( ores ) ea* o!r & ) diff]5t gangue m9]als are tol]ably con/ant1 & con/itute an important subject = ! /ud5t ( metallurgy & m9+4 ,:5 a ve9 is compos$ ( a s+le m9]al1 z qu>tz1 x may rival a dike 9 its homog5eity4 ,mo/ important ve9s1 h[ev]1 are compos$ ( sev]al or a l>ge numb] ( m9]als1 :i* may be sometimes m or less uni=mly mix$ ) ea* o!r1 b are usually di/ribut$ 9 ! fissure 9 a v irregul> mann]4 ,! great granite ve9s :i* are work$ = mica1 feldsp> & qu>tz1 are good illu/rations1 on a l>ge scale1 ( ! /ructure ( ve9s 9 :i* sev]al m9]als h be5 deposit$ cotemporane\sly4 ,! individual m9]als are f\nd to a l>ge ext5t1 9 great1 irregul> masses1 ) no ord] obs]vable 9 _! arrangem5t4 ,:5 a m9]al is deposit$ f solution1 x cry/allizes by pref]5ce on a surface ( simil> composition1 ?us qu>tz on qu>tz1 feldsp> on feldsp>1 & s on2 & x seems probable t ?is selective action ( ! wall-rock may be a pr9cipal cause ( ! irregul> di/ribution ( m9]als 9 ve9s4 ,x has (t5 be5 obs]v$ 9 metallif]\s ve9s t ! ri*ness v>ies ) ! nature ( ! adjac5t c\ntry rock4 ,?is dep5d5ce ( ! cont5ts ( a fissure ^u ! wall-rock may be due 9 "p to ! selective deposition ( ! m9]als1 & 9 "p to _! d]ivation f ! contigu\s portions ( ! c\ntry or wall-rock1 z 9 ! s-call$ segregat$ ve9s4 ,temp]ature & pressure ex]t an important influ5ce ^u *emical precipitation1 & x is1 !re=e1 probable t ! composition ( _m ve9s v>ies ) ! dep?4 ,illu/ration3 ,fig4 #ae4--;,ideal section ( a ve94 ,frequ5tly1 p]haps usually1 ! m9]als ( composite ve9s are deposit$ 9 succession1 in/ead ( cotemporane\sly1 giv+ rise to ! rem>kable b&$ /ructure s *>act]i/ic ( ?is class ( ve9s4 ,! fir/ m9]al deposit$ 9 ! fissure =ms a lay] cov]+ ea* wall1 & is 9 turn cov]$ by lay]s ( ! second m9]al1 & t by ! ?ird1 & s on1 until ! fissure is fill$1 or ! solution exhau/$4 ,! di/+ui%+ features ( ?is /ructure are %[n 9 ,fig4 #ae1 9 :i* w w repres5ts ! wall-rock1 a a1 b b1 c c are successive lay]s ( qu>tz1 fluorite & b>ite1 & ! c5tral b&1 d1 is gal5ite4 ,s9ce ! ve9 gr[s f ! outside inw>d1 ! out] lay]s are ! olde/1 & ! c5tral lay]s are ! newe/2 aga91 ! lay]s are symmetrically arrang$1 be+ repeat$ 9 ! rev]se ord] on opposite sides ( ! middle ( ! ve92 &1 la/ly1 9 lay]s compos$ ( prismatic cry/als1 z qu>tz 7see ! figure72 ! cry/als are p]p5dicul> to ! wall & (t5 project into1 & ev5 ?r\gh1 ! succe$+ lay]s4 ,su* a cry/all9e lay] is call$ a 8comb0 & ! int]lock+ ( ! lay]s 9 ?is way is describ$ z ! comb-/ructure ( ! ve94 ,! b&+ ( ve9s is ?us /rongly contra/$ ) /ratification1 & ) ! /ructure 9 dikes due to ! m rapid cool+ along ! walls4 ,! duplicate lay]s are (t5 discont9u\s & ( unequal ?ickness1 on acc\nt ( ! /rong t5d5cy to segregation 9 ! mat]ials4 ,?is is cle>ly %[n 9 ,fig4 #af1 drawn on a r$uc$ scale f a poli%$ section ( a lead ve9 9 ,cumb]l&1 ,engl&1 conta9$ 9 ! ,museum ( ! ,bo/on ,society ( ,natural ,hi/ory4 ,9 ?is ! gangue m9]als are fluorite 7f7 & b>ite 7b74 ,! c5tral b& 7f g7 is a d>k] fluorite conta9+ irregul> masses ( gal5ite4 ,! b&$ /ructure ( ve9s is exactly reproduc$ 9 m9iature 9 ! b&+ ( agates1 geodes1 & ! amygdules =m$ 9 old lavas4 ,unfill$ cavities frequ5tly rema9 along ! middle ( ! ve94 ,:5 small1 ^! are kn[n z 8pockets40 ,!y are commonly l9$ ) cry/als2 & :5 ! latt] are m9ute1 ! pockets are call$ druses4 ,9 metallif]\s ve9s1 ! ore is mu* m abundant 9 "s p>ts ?an 9 o!rs1 & ^! ore-bodies1 especially :5 some:at def9ite 9 outl9e1 are kn[n 9 _! diff]5t =ms & 9 diff]5t localities1 z c\rses1 slants1 %oots1 *imneys1 & bonanzas ( ore4 ,! int]sections & junctions ( ve9s are (t5 among ! ri*e/ p>ts1 z if ! meet+ ( dissimil> solutions _h det]m9$ ! precipitation ( ! ore4 ,illu/ration3 ,fig4 #af4--,section ( a lead ve91 "o-fif? natural size4 ,metallif]\s ve9s1 especially1 are usually deeply decompos$ along ! outcrop by ! action ( atmosph]ic ag5cies4 ,! ore is oxidiz$1 & to a l>ge ext5t remov$ by solution1 leav+ ! qu>tz & o!r gangue m9]als 9 a por\s /ate1 /a9$ by oxides ( iron1 copp]1 & o!r metals1 =m+ ! gossan or blossom-rock ( ! ve94 ,,peculi> ,,types ,,( ,,ve9s4--,9 calc>e\s or lime/one =mations1 especially1 ! jo9t-cracks & b$d+-cracks are (t5 wid5$ ?r\gh ! solution ( ! rock by infiltrat+ wat]1 & ?us become ! *annels ( a m or less ext5sive subt]ranean dra9age1 by :i* !y are m rapidly enl>g$ to a sy/em ( gall]ies & *amb]s1 &1 9 "s cases1 l>ge lime/one cav]ns4 ,! wat] dripp+ into ! cav]n f ! ov]ly+ lime/one is highly *>g$ ) c>bonate ( lime1 :i* is l>gely deposit$ on ! ceil+ & floor ( ! cav]n1 =m+ /alactitic & /alagmitic deposits4 ,^! are masses ( m9]al matt] deposit$ f solution 9 cavities 9 ! e>?'s cru/1 & are ess5tially ve9-=mations4 ,portions ( cav]ns des]t$ by ! fl[+ /reams by :i* !y 7 excavat$1 are (t5 fill$ up 9 ?is way1 be+ conv]t$ into irregul> ve9s ( calcite4 ,b calcite is n ! only m9]al f\nd 9 ^! cav]n deposits1 = b>ite & fluorite1 & v>i\s lead & z9c ores1 especially ! sulphides ( ^! metals--gal5ite & sphal]ite--h also be5 lea*$ out ( ! surr\nd+ lime/one & conc5trat$ 9 ! cav]ns4 ,! celebrat$ lead m9es ( ! ,mississippi ,valley1 & "s ( ! ri*e/ silv]-lead m9es ( ,utah & ,nevada are ( ?is "*4 ,! =ms ( ^! cav]n-deposits v>y almo/ indef9itely1 & are (t5 highly irregul>4 ,! pr9cipal types are kn[n z ga%-ve9s1 flats & %eets 7,fig4 #ag71 *amb]s & pockets4 ,:]e jo9ts & o!r cracks h op5$ slightly 9 diff]5t directions & become fill$ ) infiltrat$ ores1 we h :at ! ,g]man m9]s call a /ock-"w1--an irregul> network ( small & int]lac+ ve9s4 ,illu/ration3 ,fig4 #ag4--;,ga%-ve9s & %eets4 ,an impregnation is an irregul> segregation ( metallif]\s m9]als 9 ! mass ( "s eruptive or cry/all9e rock4 ,its outl9es are n %>ply def9$1 b x %ades (f gradually into ! enclos+ rock4 ,fahlb&s are simil> ill-def9$ deposits or segregations 9 /ratifi$ rocks4 ,an impregnation or ve9 occurr+ along ! contact betwe5 two dissimil> rocks is call$ a contact deposit4 ,^! are usually f\nd betwe5 =mations ( diff]5t geological ages1 & especially betwe5 eruptive & s$im5t>y rocks4 ,subsequ5t ,/ructures produc$ by ,subt]ranean ,ag5cies4 ,! subt]ranean =ces conc]n$ 9 ! =mation ( rocks are *iefly v>i\s manife/ations ( t enorm\s tang5tial pressure develop$ 9 ! e>?'s cru/1 p>tly by ! cool+ & %r9kage ( its int]ior1 b l>gely1 x is probable1 by ! dim9ution ( ! velocity ( ! e>?'s rotation by tidal friction1 & ! consequ5t dim9ution ( ! oblat5ess ( its =m4 ,x is well kn[n t ! c5trifugal =ce aris+ f ! e>?'s rotation is suffici5t to *ange ! o!rwise sph]ical =m ( ! e>? to an oblate sph]oid1 ) a diff]5ce ( tw5ty-six miles betwe5 ! equatorial & pol> diamet]s4 ,x is also well kn[n t :ile ! e>? turns f we/ to ea/ on its axis1 ! tidal wave moves ar\nd ! globe f ea/ to we/1 ?us act+ l a p[]ful friction-brake to /op ! e>?'s rotation4 ,our day is consequ5tly l5g!n+1 & ! e>?'s =m z gradually approa*+ ! p]fect sph]e4 ,?is means a v decid$ %ort5+ & consequ5t crumpl+ ( ! equatorial circumf]5ce1 & is equival5t to a m>k$ %r9kage ( ! e>?'s int]ior1 s f> z ! equatorial regions are conc]n$4 ,! mo/ important & direct result ( ! horizontal ?ru/1 :e!r due to cool+ or tidal friction1 is ! corrugation or wr9kl+ ( ! cru/2 & ! e>?-wr9kles are ( ?ree ord]s ( magnitude1--cont95ts1 m\nta9-ranges1 & rock-folds or ar*es4 ,cont95ts & ocean-bas9s1 al?\gh ! mo/ important & p]man5t /ructural features ( ! e>?'s cru/1 d n dem& fur!r consid]ation "h1 s9ce _! =ms & relations are adequately describ$ 9 ! bett] text-books ( physical geography4 ,! =ms & di/ribution ( m\nta9-ranges might be dismiss$ 9 ! same way2 b1 unlike cont95ts1 ! /ructure ( m\nta9s1 ^u :i* _! reliefs ma9ly dep5d1 is q fully expos$ to our obs]vation1 & is "o ( ! mo/ important fields ( ! /ud5t ( /ructural geology4 ,m\nta9s1 h[ev]1 z previ\sly expla9$1 comb9e ne>ly all ! k9ds ( /ructure produc$ by ! subt]ranean ag5cies1 & _! consid]ation1 !re=e1 belongs at ! end r ?an ! beg9n+ ( ?is section4 ,,incl9$ ,,or ,,fold$ ,,/rata4--,normally1 /rata are horizontal1 & dikes & ve9s are v]tical or ne>ly s4 ,h5ce ! /ratifi$ rocks are m expos$ to ! crumpl+ action ( ! tang5tial pressure 9 ! e>?'s cru/ ?an ! eruptive & ve9 rocks2 & x is = ?is reason & p>tly because ! /ratifi$ rocks are va/ly m abundant ?an ! o!r k9ds1 t ! effects ( ! corrugation ( ! cru/ are /udi$ *iefly 9 ! =m]4 ,b x %\ld be und]/ood t fold$ dikes & ve9s are n uncommon4 ,t ! /ratifi$ rocks h1 9 _m in/ances1 suff]$ great di/urbance subsequ5t to _! deposition1 is v evid5t2 =1 :ile ! /rata mu/ h be5 orig9ally approximately /raight & horizontal1 !y are n[ (t5 curv$1 or %>ply b5t & contort$1 & highly incl9$ or ev5 v]tical4 ,all incl9$ b$s or /rata are portions ( great folds or ar*es4 ,?us we may feel sure :5 we see a /ratum slop+ d[nw>d into ! gr\nd1 t its incl9ation or dip does n cont9ue at ! same angle1 b t at "s mod]ate dep? x gradually *anges & ! b$ rises to ! surface aga94 ,simil>ly1 if we look 9 ! opposite direction & ?9k ( ! b$ z slop+ upw>d--we "k t ! surface ( ! gr\nd is be+ con/antly l[]$ by erosion1 & consequ5tly t ! incl9$ /ratum =m]ly ext5d$ high] ?an x does n[1 b n indef9itely high]2 =1 9 imag9ation1 we see x curv+ & desc5d+ to ! level ( ! pres5t surface aga94 ,h5ce x =ms1 at ! same "t1 "p ( "o side ( a great concave ar*1 & ( a great convex ar*1 j z e incl9$ surface on ! gr\nd indicates bo? a hill & a valley4 ,& guid$ by ?is pr9ciple we c (t5 recon/ruct ) mu* probability folds t h be5 m or less completely swept away by erosion1 or t are buri$ beyond our sight 9 ! e>?'s cru/4 ,! ar*es ( ! /rata are r>ely di/9ctly indicat$ 9 ! topography1 b mu/ be /udi$ :]e ! gr\nd has be5 p>tly dissect$1 z 9 cliffs1 gorges1 qu>ries1 etc4 ,!y are also1 z a rule1 f> m irregul> & complex ?an !y are usually conceiv$ or repres5t$4 ,! wr9kles ( our clo?+ are (t5 bett] illu/rations ( rock-folds ?an ! models & diagrams us$ = t purpose4 ,?is becomes self-evid5t :5 we reflect t ! e>?'s cru/ is exce$+ly het]og5e\s 9 composition & /ructure1 & mu/1 !re=e1 yield unequally to ! unequal /ra9s impos$ ^u x4 ,! folds or undulations ( ! /rata may be pr(itably comp>$ ) wat]-waves4 ,9 fact1 ! comp>ison is s close t !y h be5 n inaptly call$ rock-waves4 ,folds1 l waves1 unless v l>ge1 r>ely cont9ue = any great di/ance1 b die out & are replac$ by o!rs1 giv+ rise to ! en e*elon or /ep-l arrangem5t4 ,! plan ( bo? a wave & a fold is a m or less elongat$ ellipse1 ea* /ratum 9 a fold be+ semi-ellipsoidal or boat-%ap$4 ,9 o!r words1 a normal fold is an elongat$ m\nd ( conc5tric /rata1 be+ highe/ at ! c5tre1 slop+ v gradually t[>d ! ends1 & mu* m abruptly t[>d ! sides4 ,illu/ration3 ,fig4 #ah4--;,anticl9al & syncl9al folds4 ,! imag9>y l9e pass+ longitud9ally ?r\gh a fold1 ab\t :i* ! /rata appe> to be b5t1 is ! axis2 & ! plane ly+ midway betwe5 ! two sides ( a fold & includ+ ! axis is ! axial plane4 ,! two pr9cipal k9ds ( folds are ! anticl9e 7,fig4 #ah1 ,a71 :]e ! /rata dip away f ! axis2 & ! syncl9e 7,fig4 #ah1 ,b71 :]e !y dip t[>d ! axis4 ,!y are commonly1 b n always1 correlative1 l hill & valley4 ,rock-folds are ( all sizes1 f almo/ microscopic wr9kles to great ar*es miles 9 l5g? & bread?1 & ?\s&s ( feet 9 height4 ,! small] folds1 or su* z may be se5 9 h& specim5s & ev5 9 consid]able blocks ( /one1 are commonly call$ contortions1 & x is int]e/+ to obs]ve t !y are1 9 ne>ly ev]y?+ except size1 precisely l ! l>ge folds1 s t !y answ] admirably z geological models4 ,l>ge folds1 h[ev]1 are almo/ necess>ily curves1 b contortions are frequ5tly angul> 7,fig4 #ai74 ,) folds1 z ) waves1 ! small undulations are borne ^u ! l>ge ones2 b ! contortions are n uni=mly di/ribut$4 ,an inspection ( ,fig4 #ah %[s t :5 ! rocks are fold$ !y mu/ be 9 a /ate ( t5sion on ! anticl9es 7,a71 & 9 a /ate ( compression 9 ! syncl9es 7,b71 & ! latt] is evid5tly ! normal position ( ! puck]+s or contortions ( ! /rata1 z %[n 9 ,fig4 #bj4 ,contortions are also mo/ commonly f\nd 9 ?9-b$d$1 flexible rocks1 su* z %ales & s*i/s4 ,& :5 we f9d !m 9 h>d1 rigid rocks1 l gneiss & lime/one1 x mu/ mean ei!r t ! /ructure 0 develop$ ) extreme sl[ness1 or t ! rock 0 m flexible !n & possibly pla/ic4 ,illu/ration3 ,fig4 #ai4--;,contort$ /rata4 ,illu/ration3 ,fig4 #bj4--;,contort$ syncl9e4 ,illu/ration3 ,fig4 #ba4--,section ( anticl9al m\nta9s4 ,x is v int]e/+ to notice ! relations ( anticl9al & syncl9al folds to ! ag5ts ( erosion4 ,at ! "t ! folds are made1 ! anticl9als1 ( c\rse1 are ridges1 & ! syncl9als1 valleys1 & ?is relation sometimes cont9ues1 z %[n 9 ,fig4 #ba2 b we h se5 t ! rocks 9 ! tr\gh ( ! syncl9al are compress$ & compact$1 i4e41 made m capable ( resi/+ erosion1 :ile ^? on ! cre/ ( ! anticl9al are /ret*$ & brok51 i4e41 made m susceptible ( erosion4 ,! consequ5ce is t ! anticl9als are usually worn away v mu* fa/] ?an ! syncl9als2 s mu* fa/] t 9 _m cases ! topographic features are completely transpos$1 & 9 place ( anticl9al ridges & syncl9al valleys 7,fig4 #ba7 we f9d syncl9al ridges & anticl9al valleys 7,fig4 #bb74 ,illu/ration3 ,fig4 #bb4--,section ( syncl9al m\nta9s4 ,illu/ration3 ,fig4 #bc4--,monocl9al fold4 ,illu/ration3 ,fig4 #bd4--,unsymmetrical & inv]t$ folds4 ,besides ! anticl9al & syncl9al folds already expla9$1 !re are folds t slope 9 only "o direction1 "o-sid$ or monocl9al folds 7,fig4 #bc74 ,anticl9al & syncl9al folds are symmetrical :5 ! dip or slope ( ! /rata is ! same on bo? sides & ! axial plane is v]tical4 ,! great majority ( folds1 h[ev]1 are unsymmetrical1 ! opposite slopes be+ unequal1 & ! axial planes incl9$ to ! v]tical 7,fig4 #bd1 ,a74 ,?is means t ! compress+ or plicat+ =ce has be5 great] f "o side ?an f ! o!r1 z indicat$ by ! arr[s4 ,x act$ ) ! greate/ int5sity on ! side ( ! g5tl] slope1 ! t5d5cy evid5tly hav+ be5 to cr[d or tip ! fold ov] 9 ! direction ( ! /eep slope4 ,:5 ! /eep slope approa*es ! v]tical1 ?is t5d5cy is almo/ unresi/$1 & :5 x passes ! v]tical1 gravitation assi/s 9 ov]turn+ ! fold 7,fig4 #bd1 ,b74 ,su* highly unsymmetrical folds1 includ+ all cases :]e ! two sides ( ! fold slope 9 ! same direction1 are describ$ z ov]turn$ or inv]t$1 al?\gh ! latt] t]m is n /rictly applicable to ! entire fold1 b only to ! /rata compos+ ! "u or lee side ( x4 ,fig4 #bd1 ,b1 %[s t ^! b$s are completely inv]t$1 ! old]1 z ! figures indicate1 ly+ con=mably ^u ! new]4 ,?is inv]sion is "o ( ! mo/ important features ( fold$ /rata1 & x has l$ to _m mi/akes 9 det]m9+ _! ord] ( succession4 ,9 ! great m\nta9-*a9s1 especially1 x is exhibit$ on ! gr&e/ scale1 great gr\ps ( /rata be+ fold$ ov] & ov] ea* o!r z we might fold c>pets4 ,an inv]t$ /ratum is l a flatt5$ ,s or ,z1 & may be pi]c$ by a v]tical %aft ?ree times1 z has actually happ5$ 9 "s coal m9es4 ,folds are op5 :5 ! sides are n p>allel1 & clos$ :5 !y are p>allel1 ! =m] be+ repres5t$ by a half-op51 & ! latt] by a clos$1 book4 ,clos$ folds are usually inv]t$1 & :5 ! tops h be5 remov$ by erosion 7,fig4 #be71 ! repetition ( ! /rata may escape detection1 & ! ?ickness ( ! section be1 9 consequ5ce1 greatly ov]e/imat$4 ,?us1 a geologi/ trav]s+ ! section 9 ,fig4 #be w\ld see ?irty-two /rata1 all incl9$ to ! left at ! same angle1 ^? on ! "r app>5tly pass+ bel[ ^? on ! left1 & all =m+ "p ( "o great fold4 ,! repetition ( ! /rata 9 rev]se ord]1 z indicat$ by ! numb]s1 & ! /ructure bel[ ! surface1 %[1 h[ev]1 t ! section really consi/s ( only f\r b$s involv$ 9 a s]ies ( f\r clos$ folds1 ! true ?ickness ( ! b$s 9 ?is section be+ only "o-eigh? z great z ! app>5t ?ickness4 ,illu/ration3 ,fig4 #be4--,s]ies ( clos$ folds4 ,! mo/ important features to be not$ 9 obs]v+ & describ+ incl9$ or fold$ /rata are ! /rike & dip4 ,! /rike is ! compass be>+ or horizontal direction ( ! /rata4 ,x is ! direction ( ! outcrop ( ! /rata :]e ! gr\nd is level4 ,x may also be def9$ z ! direction ( a level l9e on ! surface ( a /ratum1 & is usually p>allel ) ! axis ( ! fold4 ,illu/ration3 ,fig4 #bf4--;,dip & /rike4 ,! dip is ! incl9ation ( ! b$s to ! plane ( ! horizon1 & embraces two elem5ts3 7a7 ! direction ( ! dip1 :i* is always at "r angles to ! /rike1 be+ ! l9e ( /eepe/ desc5t on ! surface ( ! /ratum1 & 7b7 ! am\nt ( ! dip1 :i* is ! value ( ! angle betwe5 ! l9e ( /eepe/ desc5t & ! horizon4 ,9 ,fig4 #bf1 s t is ! direction ( ! /rike1 & d p t ( ! dip4 ,! /rike & direction ( ! dip are det]m9$ ) ! compass1 & ! am\nt ( ! dip ) ! cl9omet]1 an in/rum5t = measur+ v]tical angles4 ,! /rike is mu* less v>iable ?an ! dip1 be+ (t5 ess5tially con/ant ov] ext5sive di/ricts2 :ile ! dip1 except 9 v l>ge or clos$ folds1 is con/antly *ang+ 9 direction & am\nt4 ,:5 ! dip & surface bread? ( a s]ies ( /rata h be5 measur$1 x is a simple problem 9 trigonometry to det]m9e ! true ?ickness1 & ! dep? bel[ ! surface ( any p>ticul> /ratum at any giv5 di/ance f its outcrop4 ,:5 ! /rata are v]tical1 ! surface bread? or trav]se measure is equal to ! ?ickness4 ,by ! outcrop ( a /ratum or =mation we ord9>ily und]/& its actual exposure on ! surface1 :]e x projects ?r\gh ! soil 9 l$ges or qu>ries4 ,b ! t]m is also m broadly def9$ to mean ! exposure ( ! /ratum z x w\ld appe> if ! soil 7 entirely remov$4 ,x is in/ructive to obs]ve ! relations ( ! outcrop to ! =m ( ! surface4 ,its bread? v>ies ) its incl9ation to ! surface1 appe>+ n>r[ & %[+ its true ?ickness :]e x is p]p5dicul> to ! surface1 & broad5+ out rapidly :]e ! surface cuts x obliquely4 ,! outcrops ( horizontal /rata =m level l9es or b&s along ! sides ( hills & valleys1 ess5tially cont\r l9es 9 ! topography2 & appe> z irregul>1 s9u\s b&s bord]+ ! /reams & valleys 9 ! map-view ( ! c\ntry4 ,! outcrops ( v]tical /rata1 dikes1 or ve9s1 on ! o!r h&1 are repres5t$ by /raight l9es & b&s on ! map4 ,:ile ! outcrops ( incl9$ /rata are deflect$ to ! "r or left 9 cross+ ridges & valleys1 accord+ to ! direction & am\nt ( _! incl9ation4 ,a geological map %[s ! surface di/ribution ( ! rocks1 i4e41 gives 9 "o view ! =ms & arrangem5t ( ! outcrops ( all ! rocks 9 ! di/rict mapp$1 includ+ ! tr5d or /rike ( ! fold$ /rata4 ,! map may be li?ological1 ea* k9d ( rock1 z granite1 s&/one1 lime/one1 etc41 be+ repres5t$ by a diff]5t color2 or1 x may be hi/orical1 ea* color repres5t+ "o geological =mation1 i4e41 ! rocks =m$ dur+ "o p]iod ( geological "t1 )\t ref]5ce to _! li?ological "*4 ,b 9 ! be/ maps ^! two me?ods are comb9$4 ,! geological section %[s ! arrangem5t ( ! rocks bel[ ! surface1 reveal+ ! dip ( ! /rata & supplem5t+ ! map1 bo? modes ( repres5tation1 ! horizontal & v]tical1 be+ requir$ to give a complete idea ( ! geological /ructure ( a c\ntry4 ,= a detail$ & satisfactory explanation ( ! con/ruction & use ( geological maps & sections1 /ud5ts are ref]r$ to ,pr(4 ,geikie's 8,outl9es ( ,field ,geology40 ,,cleavage ,,/ructure4--,?is important /ructure is n[ kn[n to be1 l rock-folds1 a direct result ( ! great horizontal pressure 9 ! e>?'s cru/4 ,x is entirely di/9ct 9 its nature & orig9 f cry/all9e cleavage1 & may prop]ly be call$ li?ologic cleavage4 ,x is also ess5tially unlike /ratification & jo9t-/ructure4 ,x agrees ) /ratification 9 divid+ ! rocks into ?9 p>allel lay]s1 b ! cleavage planes are normally v]tical in/ead ( horizontal4 ,& ! cleavage planes diff] f jo9ts 9 runn+ 9 only "o direction1 divid+ ! rock into lay]s2 :ile jo9ts1 z we %all see1 trav]se ! same mass ( rock 9 v>i\s directions1 divid+ x into blocks4 ,illu/ration3 ,fig4 #bg4--,slaty cleavage 9 contort$ /rata4 ,! pr9cipal *>act]i/ics ( li?ologic cleavage are3 7#a7 ,x is r>e1 except 9 f9e-gra9$1 s(t rocks1 hav+ its be/ developm5t 9 ! slates1 ro(+ slates & s*ool slates af=d+ typical examples4 ,h5ce x is commonly kn[n z slaty cleavage4 7#b7 ,! cleavage planes are highly incl9$ or v]tical1 v con/ant 9 dip & /rike1 & q indep5d5t ( /ratification4 7#c7 ,x is usually associat$ ) fold$ /rata1 & (t5 ) di/ort$ nodules or fossils4 ,! m important ( ^! *>act]i/ics are illu/rat$ by ,fig4 #bg4 ,?is repres5ts a block ( contort$ /rata 9 :i* ! d>k lay]s are slate ) v p]fect cleavage p>allel to ! left-h& %ad$ side ( ! block2 :ile ! :ite lay]s are s&/one & q de/itute ( cleavage4 ,_m explanations ( ?is int]e/+ /ructure h be5 propos$1 b t fir/ advanc$ by ,%>pe may be reg>d$ z fully e/abli%$4 ,he said t slaty cleavage is always due to p[]ful pressure at "r angles to ! planes ( cleavage4 ,all ! *>act]i/ics ( cleavage not$ above are 9 h>mony ) ?is !ory4 ,cleavage is limit$ to f9e-gra9$ or s(t rocks1 because ^! alone c be modifi$ int]nally by pressure1 )\t rupture4 ,h>d] & m rigid rocks may be b5t or brok51 b !y appe> insusceptible ( m9ute wr9kl+ or o!r *ange ( /ructure affect+ e p>ticle ( ! mass4 ,s9ce ! cleavage planes are normally v]tical1 ! pressure1 accord+ to ! !ory1 mu/ be horizontal4 ,t ?is horizontal pressure exi/s & is adequate 9 direction & am\nt1 is prov$ by ! folds & contortions ( ! cleav$ /rata2 =1 z %[n 9 ,fig4 #bg1 ! cleavage planes co9cide ) ! /rike ( ! fold+s1 & are ?us p]p5dicul> to ! pressure horizontally z well z v]tically4 ,! di/ortion ( ! fossils 9 cleav$ slates is pla9ly due to pressure at "r angles to ! cleavage1 = !y are compress$ or %ort5$ 9 t direction1 & ext5d$ or flatt5$ out 9 ! planes ( cleavage4 ,aga91 ,tyndall has %[n t ! magnetism ( cleav$ slate proves t x has be5 p[]fully compress$ p]p5dicul>ly to ! cleavage4 ,&1 f9ally1 repeat$ exp]im5ts by ,sorby & o!rs h prov$ t a v p]fect cleavage may be develop$ 9 clay 7unconsolidat$ slate7 by compression1 ! planes ( cleavage be+ at "r angles to ! l9e ( pressure4 ,:51 h[ev]1 ,%>pe's !ory _h be5 ?us fully demon/rat$1 ! "q z to h[ pressure produces cleavage /ill rema9$ unansw]$4 ,sorby held t clay conta9s =eign p>ticles ) unequal axes1 su* z mica-scales1 etc41 & t ^! are turn$ by ! pressure s z to lie 9 p>allel planes p]p5dicul> to its l9e ( action1 ?us produc+ easy splitt+ or cleavage 9 ^? planes4 ,& he prov$ by exp]im5ts t a mixture ( clay & mica-scales does behave 9 ?is way4 ,b ,tyndall %[$ t ! cleavage is m p]fect j 9 proportion z ! clay is free f =eign p>ticles1 & 9 su* a p]fectly homog5e\s sub/ance z beeswax1 he develop$ a m p]fect cleavage ?an is possible 9 clay4 ,8 !ory1 :i* is n[ univ]sally accept$1 is1 t ! clay itself is compos$ ( gra9s :i* are flatt5$ by pressure1 ! granul> /ructure ) irregul> fracture 9 all directions1 *ang+ to a scaly /ructure ) v easy & plane fracture or splitt+ 9 "o def9ite direction4 ,obs]vations on di/ort$ fossils & nodules h %[n t :5 slaty cleavage is develop$1 ! rock is1 on ! av]age1 r$uc$ 9 ! direction ( ! pressure to two-fif?s ( its orig9al ext5t1 & correspond+ly ext5d$ 9 ! v]tical direction4 ,?us1 :e!r rocks yield to ! horizontal pressure 9 ! e>?'s cru/1 by fold+ & corrugation1 or by ! flatt5+ ( _! con/itu5t p>ticles1 !y are alike %ort5$ horizontally & ext5d$ v]tically2 & x is impossible to ov]e/imate ! importance ( ^! facts 9 ! =mation ( m\nta9s4 ,,faults ,,or ,,displacem5ts4--,we may readily conceive t ! =ces :i* 7 adequate to elevate1 corrugate1 & ev5 cru% va/ masses ( solid rock 7 also suffici5t to crack & break !m2 & s9ce ! fractures indicate t ! /ra9s h be5 appli$ unequally1 x w be se5 t unequal movem5ts ( ! p>ts mu/ (t5 result4 ,if ?is unequal movem5t takes place1 i4e41 if ! rocks on opposite sides ( a fracture ( ! e>?'s cru/ d n move toge!r1 b slip ov] ea* o!r1 a fault is produc$4 ,! two sides may move 9 opposite directions1 or 9 ! same direction b unequally1 or "o side may rema9 /ation>y :ile ! o!r moves up or d[n4 ,x is simply ess5tial t ! movem5t %\ld be unequal 9 direction1 or am\nt1 or bo?2 t !re %\ld be an actual slip1 s t /rata t 7 once cont9u\s no long] correspond 9 position1 b lie at diff]5t levels on opposite sides ( ! fracture4 ,! v]tical diff]5ce 9 movem5t is kn[n z ! ?r[1 slip1 or displacem5t ( ! fault4 ,fault-fractures r>ely approa* ! horizontal direction1 b are usually highly incl9$ or approximately v]tical4 ,:5 ! fault is incl9$1 z 9 ,fig4 #bh1 ! actual slipp+ 9 ! plane ( ! fault exce$s ! v]tical ?r[1 = ! movem5t is !n p>tly horizontal1 ! b$s be+ pull$ ap>t endwise4 ,! incl9ation ( faults1 z ( ve9s & dikes1 %\ld be measur$ f ! v]tical & call$ ! hade4 ,faults are sometimes hundr$s ( miles 9 l5g?2 & ! ?r[ may v>y f a fraction ( an in* to ?\s&s ( feet4 ,illu/ration3 ,fig4 #bh4--,section ( a normal fault4 ,illu/ration3 ,fig4 #bi4--,section ( a rev]s$ fault4 ,transv]se sections1 su* z are repres5t$ by ,fig4 #bh & _m specim5s & models1 d n give ! complete plan or idea ( a fault2 b ?is is se5 m p]fectly 9 ,fig4 #cj4 ,we le>n f ?is t a typical fault is a fracture along :i* ! /rata h sagg$ or settl$ d[n unequally4 ,! mo/ important po9t to be obs]v$ "h is t ! /rata d n drop bodily1 b are m]ely b5t1 ! ?r[ be+ greate/ at ! middle ( ! fault & gradually dim9i%+ t[>d ! ends4 ,9 o!r words1 e simple fault mu/ die out gradually2 = we _c conceive ( a fault z end+ abruptly1 except :]e x turns ^u itself s z to completely enclose a block ( ! /rata1 :i* may drop d[n bodily2 b ! fault is !n really endless4 ,a fault may be repres5t$ on a map by a l9e2 if a simple fault1 by a s+le /raight l9e4 ,b faults are (t5 comp\nd1 & are repres5t$ by bran*+ l9es2 t is1 ! e>?'s cru/ has be5 brok5 irregul>ly1 & ! p>ts adjo9+ ! fracture h sagg$ or ris5 unequally4 ,illu/ration3 ,fig4 #cj4--;,ideal view ( a complete fault4 ,! rock above an incl9$ fault1 ve91 or dike 7,fig4 #bh7 is call$ ! hang+ wall1 & t bel[ ! foot wall4 ,n[ incl9$ faults are divid$ into two classes1 accord+ to ! relative movem5ts ( ! two walls4 ,usually1 ! hang+ wall slips d[n & ! foot wall slips up1 z 9 ,fig4 #bh4 ,faults on ?is plan are s ne>ly ! univ]sal rule t !y are call$ normal faults4 ,!y indicate t ! /rata 7 9 a /ate ( t5sion1 = _! brok5 ends are pull$ ap>t horizontally1 s t a v]tical l9e may cross ! plane ( a /ratum )\t t\*+ x4 ,a few important faults h be5 obs]v$1 h[ev]1 9 :i* ! foot-wall9999no hyph5 be=e has fall5 & ! hang+-wall9999 has ris5 7,fig4 #bi74 ,^! are kn[n z rev]s$ faults2 & !y indicate t ! /rata 7 9 a /ate ( lat]al compression1 ! brok5 ends ( ! b$s hav+ be5 pu%$ horizontally pa/ ea* o!r1 s t a v]tical l9e or %aft may int]sect ! same b$ twice1 z has be5 actually demon/rat$ 9 ! case ( "s b$s ( coal4 ,illu/ration3 ,fig4 #ca4--;,explanation ( normal faults4 ,! usual explanation ( normal faults is giv5 9 ,fig4 #ca4 ,! incl9$ fractures ( ! e>?'s cru/ mu/ (t5 be conv]g+1 b\nd+1 or enclos+ l>ge ,v-%ap$ blocks 7,a1 ,b74 ,if n[1 ?r\gh any cause1 z ! fold+ ( ! /rata1 !y are br\ght into a /ate ( t5sion1 s t ! fractures are wid5$1 ! ,v-%ap$ masses1 be+ unsupport$1 settle d[n1 ! fractures b\nd+ !m becom+ normal faults1 z is se5 by trac+ ! b$ ,x ?r\gh ! dislocations4 ,! s+le fracture bel[ ! block ,a is incl9$1 & ! /ret*+ has be5 accompli%$ by slipp+ along x & fault+ ! b$ ,z z well z ,x1 ! entire section to ! "r ( ?is fracture be+ "p ( a mu* l>g] ,v-%ap$ block ! "r-h& b\nd>y ( :i* is n se54 ,b ! unit$ fracture bel[ ! block ,b be+ v]tical1 any horizontal movem5t mu/ wid5 x into a fissure1 :i* is kept op5 by ! great w$ge above & may become ! seat ( a dike or m9]al ve94 ,! b$s bel[ ! ,v may1 9 ?is case1 escape dislocation1 z is se5 by trac+ ! b$ ,z across ! fissure4 ,^! pairs ( conv]g+ normal faults are call$ tr\gh faults2 & ?is is ! only way 9 :i* we c conceive ( important faults z t]m9at+ at mod]ate dep?s bel[ ! surface1 & n affect+ ! entire ?ickness ( ! e>?'s cru/4 ,important rev]s$ faults are believ$ to occur *iefly along ! axes ( ov]turn$ anticl9es 7,fig4 #bd7 :]e ! /rata h be5 brok5 by ! unequal /ra9s1 & ^? on ! upp] side %ov$ bodily ov] ^? on ! l[] or inv]t$ side4 ,an ext5sive displacem5t ( ! /rata is sometimes accompli%$ by %ort slips along ea* ( a s]ies ( p>allel fractures1 produc+ a /ep fault4 ,faults cutt+ incl9$ or fold$ /rata are divid$ into two classes1 accord+ z !y are approximately p>allel ) ! direction ( ! dip or ( ! /rike4 ,! fir/ are kn[n z transv]se or dip faults1 & ! second z longitud9al or /rike faults4 ,! *ief int]e/ ( ei!r class consi/s 9 _! effect ^u ! outcrops ( ! fault$ /rata1 aft] erosion has remov$ ! esc>pm5t produc$ by ! dislocation4 ,illu/ration3 ,fig4 #cb4--,plan ( a dip fault4 ,dip faults cause a lat]al %ift or displacem5t ( ! outcrops1 z %[n 9 ,fig4 #cb1 :i* repres5ts a plan or map-view ( ! /rata trav]s$ by ! fault b b1 ! d[n ?r[ be+ on ! "r & ! up ?r[ on ! left4 ,! dip ( ! /rata is indicat$ by ! small arr[s & ! accompany+ figures2 & x w be obs]v$ on trac+ ! outcrop ( any /ratum1 a a1 across ! fault t x is %ift$ to ! "r4 ,if ! ?r[ ( ! fault 7 rev]s$1 ! displacem5t ( ! outcrop w\ld be rev]s$1 also4 ,/rike faults are ( two k9ds1 accord+ z !y incl9e 9 ! same direction z ! /rata1 or 9 ! contr>y direction4 ,! effect ( ! fir/ k9d is to conceal "s ( ! b$s1 z %[n 9 ,fig4 #cc1 9 :i* b$s #e & #f d n outcrop1 b we pass on ! surface abruptly f #d to #g4 ,! app>5t ?ickness ( ! section is ?us less ?an ! real ?ickness4 ,:5 ! fault incl9es aga9/ ! /rata1 on ! o!r h& 7,fig4 #cd71 ! outcrops ( c]ta9 /rata are repeat$ on ! surface2 & a numb] ( p>allel faults ( ?is k9d1 a /ep fault1 w1 l a s]ies ( clos$ folds 7,fig4 #be71 cause ! app>5t ?ickness ( ! section to greatly exce$ ! real ?ickness4 ,repetition ( ! /rata by fault+ is di/+ui%$ f repetition by fold+ by be+ 9 ! same in/ead ( ! rev]se ord]4 ,illu/ration3 ,fig4 #cc4--,/rike fault1 conceal+ /rata4 ,illu/ration3 ,fig4 #cd4--,/rike fault1 repeat+ /rata4 ,folds & faults are really closely relat$4 ,9 ! =m] ! /rata are di/urb$ & displac$ by b5d+2 9 ! latt] by break+ & slipp+2 & ! displacem5t :i* is accompli%$ by a fold may gradually *ange to a fracture & slip4 ,?is relation is especially noticeable ) monocl9al folds 7,fig4 #bc71 9 :i* ! t5d5cy to %e> or break ! b$s is (t5 v m>k$4 ,important faults are r>ely simple1 well-def9$ fractures2 b1 9 consequ5ce ( ! enorm\s friction1 ! rocks are usually m or less brok5 & cru%$1 sometimes = a bread? ( _m feet or y>ds4 ,! fragm5ts ( ! v>i\s b$s are !n /rung along ! fault 9 ! direction ( ! slipp+1 & ?is circum/ance has be5 made use ( 9 trac+ ! cont9uation ( fault$ b$s ( coal4 ,9 o!r cases ! direction ( ! slip is pla9ly indicat$ by ! b5d+ ( ! brok5 ends ( ! /rata 7,fig4 #ce71 & ! b$s are sometimes turn$ up at a high angle or ev5 ov]turn$ 9 ?is way4 ,illu/ration3 ,fig4 #ce4--,section ( b$s di/ort$ by a fault4 ,s9ce faults are n plane1 b undulat+ & (t5 highly irregul>1 fractures1 ! walls w n co9cide aft] slipp+2 & if ! rocks are h>d en\gh to resi/ ! enorm\s pressure1 ! cavities or fissures produc$ 9 ?is way may rema9 op54 ,n[ faults are cont9u\s fractures ( ! e>?'s cru/1 rea*+ d[n to an unkn[n b v great dep?2 & h5ce !y af=d ! be/ outlets = ! heat$ subt]ranean wat]s2 s t x is common to f9d an important fault m>k$ on ! surface by a l9e ( spr+s1 & ^! are (t5 !rmal4 ,! w>m m9]al wat]s on _! way to ! surface deposit "p ( ! dissolv$ m9]als 9 ! irregul> fissures along ! fault1 :i* are ?us *ang$ to m9]al ve9s4 ,?is agrees ) ! fact t ! walls ( ve9s usually %[ fault+ z well z cru%$ rock1 slick5sides1 & o!r evid5ces ( slipp+4 ,if ! e>?'s surface 7 n subject to erosion1 e fault w\ld be m>k$ on ! surface by an esc>pm5t equal 9 height to ! ?r[ ( ! fault2 &1 not)/&+ ! p[]ful t5d5cy ( erosion to oblit]ate !m1 ^! esc>pm5ts are sometimes obs]v$1 al?\gh ( dim9i%$ height4 ,?us1 accord+ to ,gilb]t1 ! ,z&ia ,m\nta9s 9 ,new ,mexico are due to a fault ( #aa1jjj feet1 leav+ an esc>pm5t /ill #gjjj feet high4 ,b1 z a rule1 !re is no esc>pm5t or m>k$ inequality ( ! surface1 ! fault1 l ! fold1 n be+ di/9ctly indicat$ 9 ! topography4 ,9 all su* cases we mu/ conclude ei!r t ! faults 7 made a v long "t ago1 or t !y h be5 =m$ ) extreme sl[ness1 s sl[ly t erosion has kept pace ) ! displacem5t1 ! esc>pm5ts be+ worn away z fa/ z =m$4 ,^! & o!r consid]ations make x q c]ta9 t ext5sive displacem5ts are n produc$ sudd5ly1 b ei!r gr[ by a sl[1 creep+ motion1 or by small slips _m times repeat$ at long int]vals ( "t4 ,,jo9ts ,,& ,,jo9t-,,/ructure4--,?is is ! mo/ univ]sal ( all rock-/ructures1 s9ce all h>d rocks & _m imp]fectly consolidat$ k9ds1 l clay1 are jo9t$4 ,jo9ts are cracks or planes ( division :i* are usually approximately v]tical & trav]se ! same mass ( rock 9 sev]al diff]5t directions4 ,!y are di/+ui%$ f /ratification planes by be+ r>ely horizontal1 & f bo? /ratification & cleavage planes by be+ actual cracks or fractures1 & by divid+ ! rock into blocks in/ead ( %eets or lay]s4 ,! art ( qu>ry+ consi/s 9 remov+ ^! natural blocks2 & mo/ ( ! broad flat surfaces ( rock expos$ 9 qu>ries1 are ! jo9t-planes 7,fig4 #cf74 ,"s ( ! mo/ famili> features ( rock-sc5]y are also due to ?is /ructure1 cliffs1 rav9es1 etc41 be+ l>gely det]m9$ 9 =m & direction by ! pr9cipal sy/ems ( jo9ts2 & we h already se5 t ! same is true ( ve9s & dikes4 ,jo9ts are divid$ by _! *>act]i/ics & modes ( orig9 into ?ree classes z foll[s3-- ,illu/ration3 ,fig4 #cf4--,qu>ry %[+ two sy/ems ( p>allel jo9ts4 #a4 ,! p>allel & int]sect+ jo9ts4--,?is is by f> ! mo/ important class1 & has its be/ developm5t 9 /ratifi$ rocks1 su* z s&/one1 slate1 lime/one1 etc4 ,^! jo9ts are /raight & cont9u\s cracks :i* may (t5 be trac$ = consid]able di/ances on ! surface4 ,!y usually run 9 sev]al def9ite directions1 be+ arrang$ 9 sets or sy/ems by _! p>allelism4 ,?us 9 ,fig4 #cf "o set ( jo9ts is repres5t$ by ! broad1 flat surfaces 9 light1 & a second set cross+ ! fir/ ne>ly at "r angles1 by ! n>r[] faces 9 %ad[4 ,by ! int]sections ( ! diff]5t sets ( jo9ts ! rock is divid$ into angul> blocks4 ,al?\gh _m explanations ( ?is class ( jo9ts h be5 propos$1 x has long be5 ! g5]al op9ion ( geologi/s t !y are due to ! contraction ( ! rocks1 i4e41 t !y are %r9kage cracks4 ,we %all soon see1 h[ev]1 t !y lack ! mo/ important *>act]s ( cracks kn[n to be due to %r9kage2 & ! pres5t writ] has advanc$ ! view t movem5ts ( ! e>?'s cru/1 & especially ! swift1 vibratory movem5ts kn[n z e>?quakes1 are a f> m adequate & probable cause4 ,x is well kn[n t e>?quakes break ! rocks2 &1 if space p]mitt$1 x c\ld be %[n t ! e>?quake-fractures mu/ possess all ! ess5tial features ( p>allel & int]sect+ jo9ts4 ,illu/ration3 ,fig4 #cg4--;,column> dike4 #b4 ,contraction jo9ts or %r9kage cracks4--,t _m cracks 9 rocks are due to %r9kage1 !re c be no d\bt4 ,! %r9kage may result f ! dry+ ( s$im5t>y rocks2 b m g5]ally f ! cool+ ( eruptive rocks4 ,e "o has notic$ 9 w>m wea!r1 ! cracks 9 lay]s ( mud or clay on ! %ore1 or :]e pools ( wat] h dri$ up2 & we h already se5 t ^! sun-cracks are (t5 pres]v$ 9 ! h>d rocks4 ,!y h c]ta9 *>act]i/ic features by :i* !y may be di/+ui%$ f ! jo9ts ( ! fir/ class4 ,!y divide ! clay into irregul>1 angul> blocks1 :i* (t5 %[ a t5d5cy to be hexagonal in/ead ( quadrangul>4 ,! cracks are cont9ually unit+ & divid+1 b are n p>allel1 & r>ely cross ea* o!r4 ,sun-cracks nev] affect m ?an a few feet 9 ?ickness ( clay1 & are an insignificant /ructural feature ( s$im5t>y rocks4 ,9 eruptive rocks1 on ! o!r h&1 ! contraction jo9ts h a v ext5sive1 &1 9 "s cases1 a v p]fect developm5t1 culm9at+ 9 ! prismatic or column> jo9t+ ( ! basaltic rocks4 ,?is rem>kable /ructure has long excit$ ! int]e/ ( geologi/s1 &1 al?\gh ! basalt columns 7 once reg>d$ z cry/als1 & lat] z a species ( concretion>y /ructure1 x is n[ g5]ally recogniz$ z ! normal result ( sl[ cool+ 9 a homog5e\s1 brittle mass4 ,! columns are normally hexagonal1 & p]p5dicul> to ! cool+ surface1 be+ v]tical 9 horizontal %eets & lava fl[s1 z 9 ! classic examples ( ! ,giant's ,causeway & ,f+al's ,cave1 & horizontal 9 v]tical dikes 7,fig4 #cg74 ,!y beg9 to gr[ on ! cool+ surface ( ! mass & gradually ext5d t[>d ! c5tre1 s t dikes frequ5tly %[ two indep5d5t sets ( columns4 #c4 ,! conc5tric jo9ts ( granitic rocks4--,9 qu>ries ( granite & o!r massive cry/all9e rocks1 x is (t5 v noticeable t ! rock is divid$ into m or less regul> lay]s by cracks :i* are approximately p>allel ) ! surface ( ! gr\nd1 "s ( ! granite hills hav+ ?us a /ructure resembl+ t ( an onion4 ,! lay]s are ?9 ne> ! surface1 become ?ick] & less di/9ct d[nw>ds1 & _c usually be trac$ bel[ a dep? ( fifty or sixty feet4 ,^! conc5tric cracks are ( great assi/ance 9 qu>ry+1 & are n[ reg>d$ z due to ! expansion ( ! sup]ficial portions ( ! granite caus$ by ! heat ( ! sun4 ,9 ref]5ce to ?is view ( _! orig9 ^! may be prop]ly call$ expansion jo9ts4 ,,/ructure ,,( ,,m\nta9-,,*a9s4--,m\nta9s are prim>ily ( two k9ds1--volcanic & non-volcanic4 ,! /ructure ( ! =m] belongs prop]ly ) ! orig9al /ructures ( ! volcanic rocks2 b ! latt]--! true m\nta9s--owe _! int]nal /ructure & altitude or relief almo/ :olly to ! crumpl+ & ma%+ toge!r ( great zones ( ! e>?'s cru/1 be+1 z already po9t$ out1 ! culm9at+ po9ts ( ! plication1 cleavage1 & fault+ ( ! /rata4 8,a m\nta9-*a9 consi/s ( a great plateau or bulge ( ! e>?'s surface1 (t5 hundr$s ( miles wide & ?\s&s ( miles long4 ,?is is usually m or less di/9ctly divid$ by great longitud9al valleys into p>allel ranges & ridges2 & ^!1 aga91 are s]rat$ along _! cre/s1 or divid$ into peaks by transv]se valleys4 ,9 _m cases ?is ideal *a9 is f> f realiz$1 b we h in/ead1 a great bulg+ ( ! e>?'s cru/ compos$ on ! surface ( an inextricable tangle ( ridges & valleys ( erosion1 runn+ 9 all directions4 ,9 all cases1 h[ev]1 ! erosion has be5 imm5se2 = ! m\nta9-*a9s are ! great !atres ( erosion z well z ( igne\s action4 ,z a g5]al fact1 all t we see1 :5 we /& on a m\nta9-*a9--e peak & valley1 e ridge & caon1 all t con/itutes sc5]y--is :olly due to erosion40--,,le ,,conte4 ,! /ructure ( m\nta9s ?us fells "u two heads3 7#a7 ,! int]nal /ructure & altitude1 :i* are due to ! action ( ! subt]ranean ag5cies4 7#b7 ,! ext]nal =ms1 ! actual relief1 :i* are ! product *iefly ( ! sup]ficial ag5cies or erosion4 ,! /udy ( m\nta9s has %[n t3 7#a7 ,!y are compos$ ( v ?ick s$im5t>y =mations4 ,?us ! s$im5t>y rocks h a ?ickness ( #dj1jjj feet 9 ! ,alleghanies2 ( #ej1jjj feet 9 ! ,alps2 & ( two to t5 miles 9 all important m\nta9-*a9s4 ,su* ?ick deposits ( s$im5ts1 z we h already se51 mu/ be =m$ on a subsid+ sea-floor1 & 9 _m m\nta9-*a9s1 z 9 ! ,alleghanies1 ! great bulk ( ^! s$im5ts are /ill bel[ ! level ( ! sea4 ,aga91 ?ick s$im5t>y deposits c only be =m$ 9 ! %all[1 m>g9al portions ( ! sea2 & :5 su* a belt ( ?ick %ore deposits yields to ! p[]ful horizontal ?ru/1 & is crumpl$ & ma%$ up1 x is greatly %ort5$ 9 ! direction ( ! pressure & ?ick5$ v]tically1 s t its upp] surface is lift$ high above ! level ( ! sea1 & a m\nta9-*a9 is =m$ & add$ to ! edge ( ! cont95t4 ,we ?us f9d an explanation ( ! important fact t on ! sev]al cont95ts1 b notably on ! two ,am]icas1 ! pr9cipal m\nta9-ranges are ne> to & p>allel ) ! coa/ l9es4 #b4 ,! m\nta9-=m+ s$im5ts are usually /rongly fold$ & fault$1 & exhibit slaty cleavage :]ev] !y are susceptible ( t /ructure2 & ! old] rocks1 especially1 9 m\nta9s are (t5 highly metamorphos$1 & are trav]s$ by num]\s ve9s & dikes1 ! infallible signs ( int5se igne\s activity4 8,9 o!r words1 m\nta9 regions h be5 ! great !atres--7#a7 ( s$im5tation be=e ! m\nta9s 7 =m$2 7#b7 ( plication & upheaval 9 ! =mation ( ! range2 & 7#c7 ( erosion :i* det]m9$ ! pres5t outl9e4 ,add to ^! ! metamorphism1 ! faults1 ve9s1 dikes1 & volcanic outbur/s1 & x is se5 t all geological ag5cies conc5trate !re40--,,le ,,conte4 ,s9ce m\nta9-ranges are great up-swell+s or bulg+s ( ! /rata1 _! /ructure is always ess5tially anticl9al2 & !y sometimes consi/ ( a s+le m or less d5ud$ anticl9e 7,fig4 #ch71 ! olde/ & l[e/ /rata expos$ =m+ ! summit ( ! range4 ,m commonly1 h[ev]1 ! s+le great ar* or uplift is modifi$ by a s]ies ( longitud9al folds1 z %[n 9 ! section ( ! ,jura ,m\nta9s 7,fig4 #ba74 ,/ill m commonly ! folds are closely press$ toge!r1 ov]turn$1 brok51 & almo/ inextricably complicat$ by small] folds1 contortions1 & slips4 ,illu/ration3 ,fig4 #ch4--;,anticl9al m\nta94 ,! /rata on ! flanks ( ! m\nta9s are usually less di/urb$ ?an ^? ne> ! axis ( ! range1 & are sometimes se5 to re/ uncon=mably aga9/ ! latt]4 ,9 ?is way x is prov$ t "s ranges are =m$ by successive upheavals4 ,b we h /ill m conclusive evid5ce t m\nta9s are =m$ ) extreme sl[ness 9 ! fact t riv]s sometimes cut directly ?r\gh important ranges4 ,?is proves1 fir/1 t ! riv] is old] ?an ! m\nta9s2 second1 t ! deep5+ ( its *annel has always kept pace ) ! elevation ( ! range4 ,,concretions ,,& ,,concretion>y ,,/ructure4--,folds1 cleavage1 faults1 & jo9ts--all ! subsequ5t /ructures consid]$ up to ?is po9t--are ! product ( me*anical =ces4 ,*emical ag5cies1 al?\gh v effici5t 9 alt]+ ! composition & texture ( rocks1 are almo/ p[]less z reg>ds ! developm5t ( rock-/ructures2 & ! only important /ructure hav+ a *emical orig9 is t nam$ above4 ,concretions are =m$ by ! segregation ( "o or m ( ! con/itu5ts ( a rock4 ,b !re are ?ree di/9ct k9ds ( segregation4 ,if ! wat] p]colat+ ?r\gh or p]vad+ a rock1 dissolves a c]ta9 m9]al & aft]w>ds deposits x 9 cavities or fissures1 amygdules1 geodes1 or ve9s are ! result4 ,if ! m9]al is deposit$ ab\t p>ticul> po9ts 9 ! mass ( ! rock1 x may =m cry/als1 ! rock becom+ porphyritic2 or x may n cry/allize1 b build up in/ead ! r\nd$ =ms call$ concretions1 ! texture or /ructure ( ! rock becom+ concretion>y4 ,a great v>iety ( m9]als occur 9 ! =m ( concretions1 b ?is mode ( occurr5ce is especially *>act]i/ic ( c]ta9 con/itu5ts ( rocks1 su* z calcite1 sid]ite1 limonite1 hematite1 & qu>tz4 ,concretions may be classifi$ accord+ to ! nature ( ! segregat+ m9]als2 & 9 ea* class we may di/+ui% ! pure f ! impure concretions4 ,a pure concretion is "o entirely compos$ ( ! segregat+ m9]al4 ,mo/ nodules ( fl9t & *]t1 qu>tz1 geodes1 concretions ( pyrite1 & _m holl[ iron-balls are good illu/rations ( ?is class4 ,9 all ^! cases ! segregat+ m9]al has be5 able 9 "s way to remove ! o!r con/itu5ts ( ! rock1 & make room = itself4 ,b 9 o!r cases x has lack$ ?is p[]1 & has be5 deposit$ betwe5 & ar\nd ! gra9s ( s&1 clay1 etc42 & ! concretions are consequ5tly impure1 be+ compos$ p>tly ( ! segregat+ m9]al1 & p>tly ( ! o!r con/itu5ts ( ! rock4 ,! calc>e\s concretions kn[n z clay-/ones are a good example ( ?is class1 be+ simply discs ( clay1 all ! m9ute int]/ices ( :i* h be5 fill$ ) segregat$ calcite4 ,! solid iron-balls are masses ( s& fill$ 9 a simil> mann] ) iron oxides4 ,concretions are ( all sizes1 f ^? ( microscopic smallness 9 "s olitic lime/ones up to ^? tw5ty-five feet or m 9 diamet] 9 "s s&/ones4 ,! po9t ( deposition1 :5 a concretion beg9s to gr[1 is (t5 det]m9$ by "s concrete p>ticle1 z a gra9 or cry/al ( ! same or a diff]5t m9]al1 a fragm5t ( a %ell1 or a bit ( vegetation1 :i* ?us becomes ! nucleus ( ! concretion4 ,! ideal or typical concretion is sph]ical2 b ! =m is influ5c$ l>gely by ! /ructure ( ! rock4 ,9 por\s rocks1 l s&/one1 !y are frequ5tly v p]fect sph]es2 b 9 imp]vi\s rocks1 l clay1 !y are flat or disc-%ap$1 because ! wat] passes mu* m freely 9 ! direction ( ! b$d+ ?an across x2 :ile ! concretions 9 lime/ones1 ! nodules ( fl9t & *]t1 are (t5 rem>kable = ! irregul>ity ( _! =ms4 ,9 all s$im5t>y rocks ! concretions are arrang$ m or less di/9ctly 9 lay]s p>allel ) ! /ratification1 :i* usually passes undi/urb$ ?r\gh ! impure concretions4 ,_m silici\s & f]rug9\s concretions are holl[1 app>5tly 9 consequ5ce ( ! contraction ( ! sub/ance aft] its segregation2 & ! %r9kage due to dry+ is /ill fur!r indicat$ by ! cracks 9 ! sept>ia /ones4 ,! holl[1 silici\s concretions are usually l9$ ) cry/als 7geodes71 :ile ! holl[ iron-balls frequ5tly enclose a small] concretion4 ,rocks (t5 h a concretion>y /ructure :5 !re are no di/9ct or sep>able concretions4 ,& ! appe>ance ( a concretion>y /ructure 7pseudo-concretions7 is (t5 ! result ( ! conc5tric decomposition ( ! rocks by wea!r+1 z expla9$ on page #ac4 ,,subsequ5t ,,/ructures ,,produc$ ,,by ,,! ,,sup]ficial ,,or ,,aque\s ,,ag5cies4--,! sup]ficial ag5cies1 z we h se5 9 ! section on dynamical geology1 are1 9 g5]al t]ms1 wat]1 air1 & organic matt]4 ,geologically consid]$1 ! results :i* !y accompli%1 may be summ$ up "u ! two heads ( deposition & erosion--! =mation ( new rocks 9 ! sea1 & ! de/ruction ( old rocks on ! l&4 ,9 ! rle ( rock-mak]s !y produce ! v important orig9al /ructures ( ! /ratifi$ rocks2 :ile z ag5ts ( erosion !y develop ! mo/ sali5t ( ! subsequ5t /ructures ( ! e>?'s cru/--! inf9itely v>i$ relief ( its surface4 ,z a g5]al rule1 to :i* rec5t volcanoes are "o important exception1 ! orig9al & subt]ranean /ructures ( rocks are only indirectly1 & (t5 v slightly1 repres5t$ 9 ! topography2 = ?is1 z we h se51 is almo/ :olly ! product ( erosion4 ,!re=e1 :at we h *iefly to consid] 9 ?is section is to :at ext5t & h[ erosion is influ5c$ by ! pre-exi/+ /ructures ( rocks4 ,horizontal or v slightly undulat+ /rata1 especially if ! upp] b$s are h>d] ?an ^? bel[1 give rise by erosion to flat-topp$ ridges or table-m\nta9s 7,fig4 #ci74 ,b if ! /rata be s(t] & ( m uni=m texture1 erosion yields r\nd$ hills1 (t5 v /eep1 & sometimes pass+ into p9nacles1 z 9 ! ,bad ,l&s ( ! we/4 ,broad1 op5 folds1 z we h se51 give1 normally1 syncl9al hills & anticl9al valleys 7,fig4 #bb71 :5 ! erosion is well advanc$4 ,b 9 m /rongly1 closely fold$ rocks ! ridges & valleys are det]m9$ *iefly by ! outcrops ( h>d] & s(t] /rata1 z %[n 9 ,fig4 #dj1 ! symmetry ( ! reliefs dep5d+ ^u ! dip ( ! /rata4 ,?is pr9ciple ( unequal h>dness or durability also det]m9es mo/ ( ! topographic features 9 regions ( metamorphic & cry/all9e rocks1 9 :i* ! /ratification is obscure or want+4 ,illu/ration3 ,fig4 #ci4--;,horizontal /rata & table-m\nta9s4 ,illu/ration3 ,fig4 #dj4--,ridges due to ! outcrops ( h>d /rata4 ,! boldness ( ! topography1 & ! relation ( dep? to wid? 9 valleys1 dep5ds l>gely ^u ! altitude above ! sea2 b p>tly1 also1 ^u ! di/ribution ( ! ra9fall1 ! dra9age *annels or valleys be+ n>r[e/ & mo/ %>ply def9$ 9 arid regions trav]s$ by riv]s d]iv+ _! wat]s f di/ant m\nta9s4 ,t ^! are ! conditions mo/ favorable = ! =mation ( caons is prov$ by ! fact t !y are fully realiz$ 9 ! great plateau c\ntry trav]s$ by ! ,colorado & its tribut>ies1 a di/rict :i* leads ! _w 9 ! magnitude & gr&eur ( its caons4 ,b deep gorges & caons w be =m$ :]ev] a consid]able altitude1 by increas+ ! erosive p[] ( ! /reams1 enables !m to deep5 _! *annels mu* m rapidly ?an ! g5]al face ( ! c\ntry is l[]$ by ra9 & fro/4 ,?is is ! secret ( su* caons z ! ,yosemite ,valley1 & ! gorge ( ! ,columbia ,riv]1 & probably ( ! fiords :i* fret ! nor?-we/ coa/s ( ?is cont95t & ,europe4 ,= a full description & illu/ration ( ! topographic types develop$ by ! action ( wat] & ice ^u ! surface ( ! l&1 & ( ! v>i\s *>act]i/ic =ms ( m>9e erosion1 tea*]s are ref]r$ to ! l>g] works nam$ 9 ! introduction1 especially ,le ,conte's ,elem5ts ( ,geology1 & to ! bett] works on physical geography4 ,we w1 9 clos+ ?is section1 m]ely glance at "s ( ! m9or erosion-=ms1 :i* are n prop]ly topographic1 b may be (t5 illu/rat$ by class-room & museum specim5s4 ,m]e wea!r+1 ! action ( ra9 & fro/1 develops v *>act]i/ic surfaces ^u diff]5t classes ( rocks1 delicately & accurately express+ 9 relief ^? slight diff]5ces 9 texture1 h>dness1 & solubility1 :i* mu/ exi/ ev5 9 ! mo/ homog5e\s rocks4 ,e "o recognizes on sight ! h>d1 smoo? surfaces ( wat]-worn rocks4 ,!y are exemplifi$ 9 bea* & riv] pebbles1 9 sea-worn cliffs1 & :]e riv]s fl[ ov] ! solid l$ges4 ,! pot-hole 7page #ag7 is a well-m>k$ & specially int]e/+ rock-=m1 due to curr5t or riv] erosion4 ,ice has also left highly *>act]i/ic traces ^u ! rocks 9 all latitudes cov]$ by ! great ice-%eet4 ,^! consi/ *iefly ( poli%$1 groov$1 & scrat*$ or /riat$ surfaces1 ! grooves & scrat*es %[+ ! direction 9 :i* ! ice mov$4 ,! organic ag5cies1 z already not$1 accompli% v little 9 ! way ( erosion1 especially 9 ! h>d rocks1 b ! rock-bor+s made by c]ta9 mollusks & e*9od]ms may be m5tion$ z "o unimportant b *>act]i/ic =m due to organic erosion4 ---------------------------------------- -------------------------------- ,,app5dix ,! foll[+ collections are especially prep>$ & arrang$ = use ) ?is text3 ,wea!r+ #a ,diabase 99#b 8 wea!r$ 99#c 8 dis9tegrat$ #d ,felsite3 ,angul> fragm5t #e 8 ,wat] r\nd$ pebble ,=mation ( ,coals 99#f ,peat #g ,lignite #h ,bitum9\s 99#i ,cannel coal #aj ,an?racite #aa ,native coke ,rock-=m+ ,m9]als 99#ab ,graphite #ac ,halite 99#ad ,limonite 99#ae ,hematite 99#af ,magnetite #ag 8 ,lode/one 99#ah ,qu>tz3 ,glassy #ai 8 ,fl9t #bj 8 ,*]t #ba ,opaliz$ wood 99#bb ,gypsum 99#bc ,calcite #bd ,dolomite #be ,sid]ite 99#bf ,hornbl5de #bg ,pyrox5e 99#bh ,muscovite #bi ,biotite 99#cj ,or?oclase #ca ,albite 99#cb ,labradorite 99#cc ,kaol9ite #cd ,talc 99#ce ,s]p5t9e #cf ,*lorite #cg ,glauconite 7,gre5 ,s&7 #ch ,*rysolite #ci ,g>net #dj ,pyrite ,s$im5t>y & ,metamorphic ,rocks 99#da ,conglom]ate3 ,breccia 99#db 8 ,pudd+-/one 99#dc ,s&3 ,qu>tz #dd 8 ,magnetite 99#de ,s&/one3 ,f]rug9\s #df 8 ,calc>e\s #dg 8 ,arkose 99#dh ,qu>tzite #di ,clay3 ,b\ld] #ej 8 ,fire 99#ea ,%ale 99#eb 8 ,c>bonace\s #ec ,slate3 ,ro(+ #ed 8 ,flag/one #ee ,porcela9ite #ef ,tripolite #eg ,silice\s ,tufa #eh ,novaculite #ei ,asphaltum #fj ,oil ,s& 99#fa ,lime/one3 ,fossilif]\s 99#fb 8 ,coqu9a 99#fc 8 ,*alk #fd 8 ,cry/all9e #fe 8 ,compact #ff 8 ,hydraulic #fg ,calc>e\s ,tufa #fh ,dolomite #fi ,rock ,salt #gj ,phosphate ,nodule 99#ga ,gneiss3 ,granitoid 99#gb 8 ,micace\s #gc 8 ,hornbl5dic #gd ,norite3 ,hyp]/h5ite 99#ge ,s*i/3 ,mica #gf 8 ,hornbl5de #gg 8 ,talc #gh 8 ,*lorite #gi ,amphibolite #hj ,soap/one #ha ,v]d ,antique 7,s]p5t9e7 ,igne\s ,rocks 99#hb ,granite3 ,b9>y #hc 8 ,muscovite 99#hd 8 ,biotite #he 8 ,hornbl5dic #hf 8 ,r$ 99#hg ,sy5ite #hh 8 ,elolite 99#hi ,diorite 99#ij ,diabase3 ,trap 99#ia ,rhyolite #ib ,tra*yte 99#ic ,obsidian #id ,pumice #ie ,petrosilex 99#if ,&esite 99#ig ,basalt #ih 8 vesicul> ,lava 99#ii ,melaphyr3 ,amygdaloidal #ajj ,volcanic ,tuff ,collection ,no4 ,f#a4 ,entire li/ ( #ajj museum size specim5s 7#c #d71 numb]$1 labell$ & m\nt$ on blocks or 9 improv$ trays1 = museum display & laboratory "w #dj4jj 7,! same1 labell$ b unm\nt$1 #cj4jj7 ,collection ,no4 ,f#b4 ,same z above1 b small museum size1 m\nt$ 9 improv$ trays 7#b #c7 #be4jj ,collection ,no4 ,f#c4 ,same z ,f#b1 b h& size specim5s 7#b #b7 #ab4ej ,collection ,no4 ,f#d4 #hj specim5s1 omitt+ ^? m>k$ 771 9 individual trays 7#b #a7 & two clo?-bo>d cases1 numb]$ to correspond ) accompany+ pr9t$ li/ 7no labels7 #e4jj ,collection ,no4 ,f#e4 #dj specim5s m>k$ 79971 m\nt$ z collection ,f#d #b4ej ,collection ,no4 ,f#f4 #ajj pupils' fragm5ts 7#a #a71 numb]$1 9 pap] bags4 7,s+le collection #a4be47 ,9 lots ( #e or m1 ea* #a4jj ,collection ,no4 ,f#g4 #hj pupils' fragm5ts 7l ,f#f74 7,s+le #a4jj47 ,9 lots ( #e or m1 ea* 4#ge ,collection ,no4 ,f#h4 #dj pupils' fragm5ts 7l ,f#f74 7,s+le #ej;c47 ,9 lots ( #e or m1 ea* 4#dj ,collection ,no4 ,f#i4 #be museum size specim5s1 illu/rat+ /ructure1 faults1 /ratification1 etc4 ,m\nt$ & labell$ #aj4jj ,= fur!r in=mation or 9 ord]+1 address ,,w>d',s ,,natural ,,sci5ce ,,e/abli%m5t #hd-ajb ,college ,ave41 ,ro*e/]1 ,n4 ,y4 ---------------------------------------- -------------------------------- ,transcrib]'s note3 ,specim5 numb]s h be5 regul>is$ z m$ium weight4 ,page #g1 #8,le,conte' *ang$ to #8,le ,conte1' 8,by ,pr(4 ,joseph ,le ,conte40 ,page #ab1 #8cont9$' *ang$ to #8cont9u$1' 8cont9u$ exposure to !0 ,page #bh1 comma *ang$ to full /op1 8associat$ ) b$s ( coal40 ,page #cd1 #8or' *ang$ to upright1 8sup]ficial or aque\s ag5cies0 ,page #if1 all in/ances ( #8p] c5t' *ang$ to #8p] c5t4'3 8#fj p] c5t401 8#cj p] c5t401 8#he p] c5t40 ,page #ig1 full /op ins]t$ aft] #8cru/1' 8( ! e>?'s cru/4 ,! "n0 ,page #aje1 specim5 numb] abs5t 9 orig9al4 ,page #ajf1 #8gre5 s&' *ang$ to #8gre5s&1' 8gre5s&1 & s]p5t9e0 ,page #ajg1 #8magnesion' *ang$ to #8magnesian1' 8! entire rock is magnesian10 ,page #ajh1 #8#gj' *ang$ to #8#fi1' 8classification on page #fi0 ,page #aad1 full /op ins]t$ aft] #8rocks1' 8! /ratifi$ rocks4 ,l0 ,page #abf1 full /op ins]t$ aft] #8ve9s1' 89 ve9s4 ,^? fissures0 ,page #adf1 in/ance ( ?\s&s =matt$ )\t comma delimit]3 8#djjj to #ejjj feet0 ,page #ahh1 in/ance ( ?\s&s =matt$ )\t comma delimit]3 8#gjjj feet high0