,illustration3 ,cover ,picture4 ,view of the entrance to ,calvin ,coolidge ,state ,forest ,park4 ,photograph was taken looking north along ,state ,highway #ajj;,a4 ,,the ,,geology ,,of ,,calvin ,,coolidge ,,state ,,forest ,by ,,harry ,w4 ,,dodge1 ,,jr4 ,,department ,,of ,,forests ,,and ,,parks ,perry ,h4 ,merrill1 ,director ,,vermont ,,development ,,commission ,,vermont ,,geological ,,survey ,charles ,g4 ,doll1 ,state ,geologist #aiei ,,the ,,geology ,,of ,,calvin ,,coolidge ,,state ,,forest ,,park ,by ,,harry ,w4 ,,dodge1 ,,jr4 ,,introduction ,each summer hundreds of eager campers1 picnickers1 hikers and sportsmen visit the ,pinney ,hollow-,bradley ,hill recreational area of the ,calvin ,coolidge ,state ,forest ,park4 ,this area is located a few miles north of ,plymouth1 ,vermont1 and is easily reached via ,state ,route #ajj;,a from either ,plymouth or ,bridgewater ,corners 7,see index map of ,vermont1 geological map74 ,the excellent camping and recreational facilities coupled with the natural scenic beauty of this region provide many visitors with an irresistible urge to return1 summer after summer1 to this same spot4 ,this pamphlet is designed for all those who visit ,coolidge ,forest ,park and especially for those who possess questioning minds and a general desire to learn more about the world around them4 ,,geology ,have you ever wondered why the present mountains and valleys are where they are and how and when they got there8 ,has the thought passed through your mind that the very rocks on which you stand or see nearby have a definite story to tell8 ,the geologist not only wonders about such things1 but through his training attempts to answer questions of this nature4 ,his everyday job includes the reconstruction of ancient land and sea areas through a careful study of the rock record4 ,he looks at the rock layers as you might the pages of a history book4 ,the professional geologist1 however1 commands many basic geological principles and 8tools of the trade0 which permit him to read more accurately the records preserved in stone4 ,first1 the basic geological principles will be explained and you will be given the proper 8tools0 for your adventure4 ,then1 you are invited to travel back through #eej million years of time to see just why ,coolidge ,state ,forest ,park is as it is today and what it was like in the distant past4 ,,basic ,,principles ,,and 8,,tools0 ,to many of you rocks are just 8rocks0 and very little thought has been given to any history which might be gained from their study4 ,probably even fewer of you realize that literally billions of years of ,earth history can be derived directly from the rock record4 ,most geologists consider the ,earth to be nearly four billion years old with man entering the picture a mere million or so years ago4 ,no human was present to record the events of billions of years of changing land and seas1 violent earth movements or the gradual evolution of life through the last #ejj million years4 ,the study of rocks and their contained evidence of past life offers the only clarification for the extremely long past history of the ,earth4 ,in order to unravel this past history the geologist accepts1 with some reservations1 three basic principles or laws4 ,the ,law of ,uniformitarianism provides an extremely important link with the past4 ,this law states that the physical and chemical forces which are attacking or building up the surface of the earth today have operated in much the same way during past geological time4 ,this means that our observations of present day environments1 such as streams1 deltas1 lakes and oceans can be applied1 after slight modification1 to the past as recorded in the rocks4 ,for example1 study of present day deltas1 such as the ,nile or ,mississippi ,river delta1 has led to the discovery of many past deltaic deposits now preserved as layers and lenses of rock4 ,this distribution pattern of sands and muds1 the nature of the life forms within each environment and many other such criteria aid the geologist in his interpretations4 ,the ,law of ,superposition provides a physical order to the many layers of rock which form the geological record4 ,compare1 for the moment1 the vast numbers of rock layers 7strata7 with the layers of a layercake4 ,as a layercake is built up each individual layer is placed one over another1 with the bottom or base layer the first to be positioned and followed by successively overlying layers4 ,if you think of the development of this cake in terms of time1 the base layer is the oldest1 the uppermost the youngest4 ,the ,law of ,superposition follows this example and states that the lowermost stratum in a sequence of rock strata is the oldest or the first to form1 while the stratum above is younger and formed at a later time4 ,some reservations do exist2 however1 in the ,forest ,park under immediate consideration this general law does apply4 ,illustration3 ,figure #a4 ,igneous dike cutting the ,pinney ,hollow formation4 ,the dike is the darker rock which trends toward the upper left of the photograph4 ,this dike is located approximately #ajj yards south of the ,pinney ,hollow ,historical ,monument and on the east side of ,state ,highway #ajj;,a4 ,the third basic principle to command is known as the ,law of ,faunal ,succession4 ,in generalized form this law states that each stratum of rock contains its own distinct group of animal or plant remains1 termed fossils1 and that these same remains can be recognized throughout the world wherever they occur4 ,since plants and animals changed through time and because their remains are found throughout the world1 it is possible to erect a worldwide time scale based upon animal and plant evolution4 ,in short1 the fossils found in particular rock are characteristic representatives of the life at the time that rock originated and the fossils found could have been entombed only at that time4 ,one stratum1 therefore1 would have a total fossil assemblage quite different from the stratum above or below4 ,without this time reference chart it would be impossible to reconstruct what did happen during any one time interval in the past4 ,in addition to these three basic laws it is necessary to mention the rudiments of rock classification4 ,the geologist divides rocks#a into three major groups which are termed ,igneous1 ,sedimentary and ,metamorphic rocks4 ,igneous rocks are those formed by the solidification of molten material4 ,this molten material was thrust into the outer crust of the earth from below and after cooling became a solid igneous rock such as granite1 or in other cases it flowed out over the surface of the earth in the form of volcanic lava4 ,some small igneous bodies1 termed dikes1 can readily be seen along ,state ,highway #ajj;,a adjacent to ,calvin ,coolidge ,state ,forest ,park 7,see photograph1 ,fig4 #a74 ,sedimentary rocks are formed in quite a different manner and differ in general appearance4 ,these are what might be considered second-hand rocks4 ,they are composed of particles derived from other rocks1 igneous1 metamorphic or older sedimentary1 which have been carried by streams1 wind or ice to a place of rest and there cemented into rock4 ,perhaps you can visualize a river which1 throughout its course1 runs over rocks of many types4 ,this river would pick up particles of rock from its bed and banks and transport these to a lake or perhaps the sea1 where the various transported materials would settle to the bottom in distinct layers4 ,the first layer deposited would become buried under thousands of tons of overlying layers of sediment whose weight and resultant pressure1 together with the presence of adequate rock-cementing material such as calcium carbonate or silica1 would cause the bottom layer to harden into rock4 ,the layered appearance of sedimentary rocks is one of their most characteristic features and these rocks are said to be bedded or composed of many individual beds of sedimentary rock4 ,sandstone1 composed of sand size particles2 shale1 originally mud2 and limestone1 once lime-rich mud1 are examples of sedimentary rocks4 ,metamorphic rocks result when igneous or sedimentary rocks are subjected to abnormal heat and pressure4 ,folding or faulting#b of rocks within the earth's crust or deep burial beneath overlying rocks or sediments commonly produce metamorphism4 ,the introduction of hot fluids during folding and faulting greatly increase the speed and degree of metamorphic conversion4 ,when igneous or sedimentary rocks are subjected to metamorphism they tend to lose their original appearance as some minerals are completely changed or altered into new minerals and most of the original minerals are oriented in one or more preferred directions4 ,the degree of heat and pressure1 type and amount of hot fluids provided and the type of rock undergoing metamorphism will determine the nature of the metamorphic rock to develop4 ,perhaps the most unfortunate effect caused by the metamorphism of sedimentary rocks1 especially when considering the history recorded in the rocks1 is that in the majority of cases all fossils originally present are either destroyed or distorted beyond recognition4 ,the absence of fossils makes age determination quite difficult and hinders definition of previous environments4 ,the rocks seen in and adjacent to ,coolidge ,state ,forest ,park1 with very few exceptions1 are metamorphic rocks which were originally sedimentary rocks4 ,luckily the metamorphism is slight and several pages of geologic history can still be read4 ,schists1 phyllites and quartzites#c1 all metamorphic rocks1 are well displayed in the ,forest ,park region4 ,the parallel arrangement of mica plates and segregation of the darker minerals into distinct layers in the schists and phyllites together with the inherited sedimentary layering in the quartzites1 impart a distinctly visible orientation to the rocks seen in the ,forest ,park4 ,the parallelism of the mica and segregation of the darker minerals in the schists and phyllites is directly related to metamorphic processes and the measurable orientation is called foliation4 ,the original sedimentary layering of the quartzites1 little changed through the metamorphism1 is referred to as bedding4 ,from all indications the foliation and bedding are practically parallel in this region and since most of the rocks represented are of the metamorphic type1 all orientation features will be referred to as foliation4 ,illustration3 ,figure #b4 ,block diagram illustrating the dip and strike of foliation4 ,the top of the block is considered an 8imaginary horizontal plane40 ,the geologist uses the terms dip and strike to describe foliation and uses conventional symbols for plotting purposes 7,see geologic map74 ,the dip of the foliation is the angle between an imaginary horizontal line and the tilt or downward slope of the foliation4 ,the strike is the compass direction of a line formed by the dipping foliation plane and its intersection with an imaginary horizontal plane 7,see block diagram1 ,fig4 #b74 ,a glance at the geological map will show that the rocks of the ,park area consistently strike north to northwest and dip to the east4 ,if you look at the foliation symbols which are plotted on the geologic map1 the straight line of the symbol indicates the strike and the black triangle points in the direction of the dip4 ,the angles of dip have not been included on the map2 however1 they average forty-five degrees down from the horizontal and toward the east or right margin of the geological map4 ,,the ,,rocks ,,of ,,calvin ,,coolidge ,,state ,,forest ,,park ,,and ,,the ,,story ,,they ,,tell ,the rocks of ,calvin ,coolidge ,state ,forest ,park can be divided into four distinct units or formations#d4 ,the geologic map shows these formations as distinct bands1 each band representing a different formation and its intersection with the ground surface4 ,each formation is1 so to speak1 stacked upon the next older with the oldest forming the western band and the youngest on the east4 ,remember that these metamorphic rock formations were originally sedimentary in nature and were deposited in a nearly horizontal position on the floor on an ancient sea4 ,the fact that they are now tilted indicates that earth movements have taken place sometime after the sedimentary rocks hardened but before the present time4 ,the ,pinney ,hollow formation1 the oldest formation of rocks seen in the ,forest ,park1 was named for the excellent exposures of this formation in ,pinney ,hollow1 a valley located along the western border of ,coolidge ,forest4 ,you can readily see this formation1 in its most typical development1 along ,state ,highway #ajj;,a about three-tenths of a mile south of the ,park entrance road4 ,here1 a historical monument which commemorates the naming of ,pinney ,hollow1 is embedded in this formation 7,see photograph1 ,fig4 #c74 ,the lean-to1 tent platform and picnic areas are situated on this formation and its rocks are easily observed4 ,it is interesting to note that some of the ,pinney ,hollow rocks seen in these camping and picnicking spots differ from the typical rocks seen along ,state ,highway #ajj;,a4 ,in fact1 some of the rocks which are dark and are classed as phyllites1 can be confused with the overlying ,ottauquechee rocks4 ,a transition zone1 several hundred feet wide1 exists between these two formations and in which the two distinct rock types are intermingled4 ,this 8mixture0 zone indicates that there was no break in the original deposition of these two formations and therefore the rock record during this time is complete4 ,illustration3 ,,geologic ,,map ,,of ,,calvin ,,coolidge ,,state ,,forest ,,park ,,index ,,map ,,of ,,vermont ,,explanation ,,trail ,,secondary ,,road 7,,good7 ,,secondary ,,road 7,,poor7 ,,state ,,route #ajj;,a ,,state ,,property ,,line ,,contour ,,line ,,with ,,elev4 ,,stream ,,foliation ,,formations ,,missisquoi ,,formation ,,bethel ,,formation ,,ottauquechee ,,formation ,,pinney ,,hollow ,,formation ,,topography ,,from ,u4,s4 ,,geological ,,survey ,,map ,,geology ,,by ,h4 ,w4 ,,dodge1 ,,jr4 ,the ,pinney ,hollow formation1 which is an estimated #b1cjj or more feet thick1 is primarily composed of pale-green schist#e with abundant white quartz layers and lenses sandwiched between the dominantly greenish colored rock4 ,originally these metamorphic rocks were sand1 mud and sandy mud deposited on a relatively shallow sea floor4 ,after burial these sediments hardened into thin layers and lenses of sandstone1 shale1 and sandy shale4 ,metamorphism has since converted many of the shale minerals into mica flakes and some of the sandy shales produced crystals of the mineral garnet4 ,the pale-green color of the ,pinney ,hollow schist is caused by the presence of the green mica-like mineral1 chlorite1 which developed during the process of metamorphism4 ,illustration3 ,figure #c4 ,the ,pinney ,hollow ,historical ,monument embedded in the ,pinney ,hollow formation4 ,the darker rock consists of pale-green schist and the white areas are quartz layers and lenses4 ,,north #bj ,,west #be ,,rods ,,from ,,this ,,spot ,,stood ,,the ,,log ,,cabin ,,of ,jonathan ,pinney ,priscilla ,grover ,pinney ,,who ,,settled ,,here ,a4,d4 #ahjj4 ,,here ,,were ,,reared ,,their ,,ten ,,children-- ,,and ,,when ,,the ,,second ,,generation ,,came ,,they ,,called ,,it ,,pinney ,,hollow ,no fossils have been found in the ,pinney ,hollow formation of this region3 however1 evidence from other parts of ,vermont indicate that these rocks are of ,cambrian or perhaps ,ordovician#f age4 ,this dates these rocks as approximately #ejj million years old4 ,the ,ottauquechee formation1 next above the ,pinney ,hollow formation and therefore younger in age1 was named for the ,ottauquechee ,river along which this formation is well exposed and was first studied in detail4 ,the ,ottauquechee ,river is located just north of ,calvin ,coolidge ,state ,forest ,park where it flows through the towns of ,bridgewater and ,bridgewater ,corners4 ,you can see this formation along ,state ,highway #ajj;,a approximately nine-tenths of a mile north of the ,park entrance road4 ,here1 the formation crops out on the west side of the road1 or on your left if traveling toward ,bridgewater ,corners 7,see photograph1 ,fig4 #d74 ,a hike along the recently diamond-blazed ,coolidge ,forest trail1 which leads from behind the ,ranger's cabin to the ,picnic area1 affords an almost continuous view of this formation4 ,the highly resistant quartzite layers within the ,ottauquechee formation are very conspicuous features along this trail as they form several ridges trending across the footpath4 ,the ,ottauquechee formation1 estimated to be #c1jjj feet thick1 contains rocks which contrast sharply with the underlying pale-green schists4 ,the formation consists of alternating black phyllite and layers1 up to several feet thick1 of dark- to light-colored quartzite4 ,the black carbonaceous color of the phyllites and dark quartzites indicate the presence of life1 either animal or plant1 during the original deposition of the sediments forming these rocks4 ,the phyllite was1 before metamorphism1 a black shale which formed from black muds rich in organic matter4 ,from studies done in areas where black muds are accumulating today it seems quite probable that the ocean waters of ,ottauquechee time were of a restricted nature1 that is to say1 the waters were stagnant due to the lack of oxygen4 ,pinney ,hollow shallow marine water conditions remained1 but for some reason1 such as a barrier of islands or shallow water sand bars1 the circulation of ocean waters was hindered1 leading to the accumulation of stagnant organic matter on the ocean bottom4 ,this organic matter gives the ,ottauquechee phyllite and some quartzites a dark to black color4 ,no fossils have been found in the ,ottauquechee formation of the ,coolidge ,forest ,park1 but1 as with the ,pinney ,hollow formation1 evidence from other areas indicates a ,cambrian or perhaps ,ordovician age for this formation4 ,illustration3 ,figure #d4 ,the ,ottauquechee formation as exposed approximately nine-tenths of a mile north of the ,park entrance road and on the west side of ,state ,highway #ajj;,a4 ,note the massive quartzite layers above1 the black phyllite below4 ,above the ,ottauquechee rocks lie those of the ,bethel formation4 ,approximately #b1jjj feet thick1 this formation is composed mainly of pale-green schist with interlaminated thin layers of white to greenish quartzite4 ,the rock presents a distinct banded appearance and contains conspicuous crystals of garnet and the black mica1 biotite4 ,the best view of this schist is found along ,state ,highway #ajj;,a and slightly over two miles north of the ,park entrance road4 ,the relatively steep rock cliffs which line the west side of this road are composed of the resistant ,bethel formation4 ,in the northeast portion of ,coolidge ,forest ,park several excellent exposures of this formation in contact with the underlying ,ottauquechee formation can be seen1 but1 to reach these areas you would have to leave the beaten trail4 ,if you are interested in visiting these contact locations it would be best to consult the geologic map for approximate directions4 ,illustration3 ,figure #e4 ,diagrammatic cross sections illustrating the geologic history of the ,calvin ,coolidge ,state ,forest ,park4 ,vertical scale greatly exaggerated4 ,patterns to designate formations in cross section ,a are repeated in cross sections ,b and ,c4 ,a4 ,horizontal layers of early paleozoic sedimentary rocks were formed4 ,this cross section extends beyond the limits of the ,park area4 ,thicknesses of rock formations are approximately proportional4 ,b4 ,during late ,ordovician or ,devonian time these sedimentary layers were folded and the rocks metamorphosed4 ,c4 ,calvin ,coolidge ,state ,forest ,park as it appears today4 ,a ,,missisquoi ,,formation ,,bethel ,,formation ,,ottauquechee ,,formation ,,pinney ,,hollow ,,formation ,b ,c ,,shelter ,,village ,,slack ,,hill ,the conditions under which the ,bethel formation was originally deposited are similar to those which existed during ,pinney ,hollow time4 ,shale1 sandy shale and thin-bedded sandstones formed under shallow water marine conditions2 however1 restriction with accompanied organic accumulation did not occur4 ,this formation is thought to be of either ,cambrian or ,ordovician age4 ,the easternmost1 and therefore youngest formation to be found in the ,park area is known as the ,missisquoi formation4 ,this formation1 which is only partially represented here1 is made up of dark phyllite1 light blue-gray schist with conspicuous crystals of garnet and biotite1 and gray quartzite4 ,the rocks of this formation can be seen along ,broad ,brook which flows north along the eastern border of ,coolidge ,state ,forest ,park4 ,this formation is considered ,ordovician in age with the conditions of deposition being quite similar to those which existed during ,ottauquechee time4 ,once again the ocean waters were restricted and organic-rich black muds accumulated in quantity on the ocean floor4 ,,the ,,geologic ,,history ,the early geologic history of ,calvin ,coolidge ,state ,forest ,park is known from the rock formations discussed in the previous section of this pamphlet4 ,the ,pinney ,hollow1 ,ottauquechee1 ,bethel and ,missisquoi formations of ,cambrian and ,ordovician age were deposited1 essentially horizontally1 from the shallow seas which covered this area #eej to #dej million years ago 7,see cross section ,a1 ,fig4 #e74 ,during some of this time these seas were at least partially restricted as evidenced by the ,ottauquechee and ,missisquoi black phyllites4 ,other ,ordovician formations were deposited on top of these four formations1 but have been completely stripped away by erosion during the millions of years since their deposition4 ,some of these later ,ordovician sediments contain great thicknesses of volcanic rocks which probably covered the ,coolidge ,park area4 ,sometime after these later ,ordovician rocks formed1 great stresses within the earth's crust folded and in some places faulted these older rocks4 ,the pressure and resultant heat created during these earth movements converted the rocks into metamorphic schists1 phyllites and quartzites which are seen today 7,see cross section ,b1 ,fig4 #e74 ,exactly when these diastropic events took place is still open to question1 but they probably occurred near the end of ,ordovician time or perhaps millions of years later during the last phases of the ,devonian ,period4 ,probably since late ,paleozoic time the ,coolidge ,park area has been subjected to breaking-down rather than building-up processes4 ,eventually this whole region was reduced to a flat plane with only a few hills1 called monadnocks1 rising above the general flatness of the landscape4 ,still later in the history of ,coolidge ,state ,forest ,park this flat plane was lifted high above its former position and streams began to shape the land into its present form4 ,the more resistant rocks were lowered by the forces of erosion at a much slower rate than the less resistant types4 ,the hills and valleys which you see today are primarily the result of this general uplift followed by the wearing away of the softer rocks at a more rapid rate than the harder rock types4 ,since the formations trend in a north-north-west direction1 the hills and valleys are also oriented in this general direction1 as the different resistive qualities of the rocks are presented in this pattern4 ,the story is not complete without mention of the last modifying influence to affect this region4 ,approximately one million years ago the first of perhaps three glacial advances began4 ,these large glacial masses1 termed continental glaciers1 slowly advanced southward over the northern sections of the ,united ,states and covered a vast region with a thick sheet of ice4 ,as these ice masses rode over the ,coolidge ,park region they tended to round-off irregular features of the landscape and to fill in certain low regions with their transported rock debris4 ,the rather smooth outlines of the hills in ,coolidge ,forest ,park and the sand and gravel deposits so apparent adjacent to nearby streams tell the story of these glacial advances and subsequent withdrawals4 ,other evidence of the overriding ice is seen in the presence of scratch marks1 termed glacial striae1 which were produced by fragments of rock as they were dragged by the moving ice across the underlying rocks4 ,along the east bank of ,broad ,brook and approximately two hundred yards south of the bridge at ,five ,corners1 abundant glacial striae are clearly displayed4 ,the orientation of these striae indicates that the glacier producing them moved from north north-west to the south south-east4 ,since the recession of the last ice sheet1 which took place several thousand years ago1 the general appearance of the ,coolidge ,park region has changed very little4 ,the streams have cut their valleys somewhat deeper and some of the glacial sands and gravels have been redistributed4 ,a few thousand years ago ,coolidge ,state ,forest ,park looked quite the same as it does today 7,see cross section ,c1 ,fig4 #e74 ,,side ,,trips ,,of ,,geological ,,interest ,gold ,panning ,there are several locations immediately adjacent to the ,calvin ,coolidge ,state ,forest ,park where some gold can still be obtained from stream sands and gravels4 ,the abandoned town of ,five ,corners offers the park visitor ample chance to 8try his luck40 ,in fact1 several local people still obtain small gold nuggets and a good deal of gold dust from the streams in the vicinity of ,five ,corners 7,see geologic map for geographic location74 ,other possible 8panning0 locations would include ,reading ,pond ,brook1 ,buffalo ,brook and ,kingdom ,brook4 ,the gold which is found is probably derived from nearby gold-bearing quartz veins4 ,the equipment needed for an afternoon of panning is relatively simple to obtain4 ,a wide1 rather shallow pan with gently sloping sides is really all that is needed4 ,gravel and sand1 which you find concentrated on the upstream side of natural rock riffles in the stream bed should be placed together with water in your pan4 ,then the pan should be rotated and the lighter rock materials decanted4 ,the heavy gold will be concentrated in the bottom of the pan4 ,asbestos and ,talc ,for you who might be interested in mineral collecting it is suggested that a trip to an old pit near ,five ,corners might prove rewarding4 ,walk down ,broad ,brook from the bridge at ,five ,corners until you locate the first small tributary entering on your left4 ,turn left up this tributary and continue to walk for approximately one hundred yards4 ,on your left you will see the remains of a pit dug into the side of the stream bank which1 at this location1 is lined with rocks of the ,ottauquechee formation4 ,you will quickly note the fibrous asbestos in the walls of this pit2 however1 if you wish to collect specimens of this mineral be extremely careful and avoid standing beneath any overhanging rock material4 ,talc1 which feels 8soapy0 to the touch1 is also abundant in this immediate area4 ,this asbestos and talc occur in a lenticular-shaped body which is perhaps eight hundred feet wide and of an undetermined length4 ,it is not certain when these minerals formed2 however1 it was probably in the early history of the region4 ,garnet ,good specimens of garnet can be found in the rocks of the ,bethel formation4 ,these garnets are not of gem quality but still offer good collecting for the amateur mineralogist4 ,good collecting localities exist along ,state ,highway #ajj;,a and at several different spots within the ,park itself4 ,a hike along the northern boundary of the ,park would intersect several excellent collecting spots4 ,vermont ,marble ,company ,exhibit1 ,proctor1 ,vermont ,if time permits1 or a rainy day arrives1 a visit to the ,vermont ,marble ,company ,exhibit in ,proctor1 ,vermont1 is highly recommended4 ,marble is a metamorphic rock which was originally sedimentary in nature4 ,lime muds hardened into limestones and then1 converted by metamorphism1 became marble4 ,the marble exhibit at ,proctor1 termed 8,the largest ,marble ,exhibit in the ,world10 displays over #ajj varieties of marble and igneous rock1 granite4 ,fossils can be seen in some of the varieties of marble1 which demonstrates that under certain conditions recognizable fossils do occur in metamorphic rocks4 ,most of the marble seen in this exhibit is quarried nearby2 however1 for safety reasons visitors are not allowed to enter the quarries4 ,it is interesting to note that these marbles are about the same age as the rocks seen in ,coolidge ,state ,forest ,park4 ,footnotes #a;,a rock1 for those desiring a more technical definition1 is any relatively hard1 naturally occurring1 combination of minerals which form an essential part of the earth4 ,minerals are composed of one or more chemical elements1 such as oxygen or silicon1 that form in nature4 #b;,a fault is a break or fracture in the rocks of the earth's crust where one side of the fracture moves in some direction relative to the other side4 ,some recent earthquakes in ,california and ,nevada have produced visible faults where1 for instance1 roads were cut and one side displaced several yards from the other4 #c,most of the mineral grains which make up a schist1 a metamorphosed shale or sandy shale1 can be seen with the naked eye1 and the parallel to subparallel arrangement of platy or flaky minerals1 such as the abundant mica1 is the most obvious feature4 ,in bright sunlight a schist presents a very shiny1 almost silvery appearance which is caused by the reflection of sunlight from the many parallel mica plates4 ,a phyllite has much the same mineral composition as that of a schist2 however1 the individual mineral grains are too small to be seen without the aid of a magnifying glass4 ,as with the schist1 a phyllite when viewed in direct sunlight1 appears shiny4 ,quartzites are metamorphosed sandstones which have been fused into great hardness through the application of heat and pressure4 #d;,a geologic formation consists of a group of similar rocks1 or sequence of rocks1 which can be easily distinguished from adjacent rocks and whose distribution can be plotted on a map4 #e,more technically this schist is termed a chlorite-sericite-quartz schist4 #f,the geologist divides geologic time into four major sections1 designated ,eras4 ,these ,eras are in turn subdivided into ,geologic ,periods which are of shorter time duration4 ,the ,cambrian ,period is the oldest of the ,paleozoic ,era and began some #eej million years ago4 ,the ,ordovician ,period is the next oldest of the ,paleozoic ,era and started about #ddj million years ago and ended close to #cfj million years ago4 ,transcriber's ,notes --,silently corrected a few typos4 --,retained publication information from the printed edition3 this e,book is public-domain in the country of publication4 --,in the text versions only1 text in italics is delimited by underscores4