,,the ,,geology ,,of ,d4,a4,r4 ,,state ,,park ,illustration3 ,shoreline at ,d4,a4,r4 ,state ,park looking south4 ,,mt4 ,,philo ,,state ,,forest ,,park ,illustration3 ,panoramic view from west overlook on ,mt4 ,philo4 ,adirondack ,mountains in background4 ,lake ,champlain and ,champlain ,lowlands in foreground4 ,,sand ,,bar ,,state ,,park ,illustration3 ,sand ,bar ,state ,park on flat surface of ,lamoille ,river delta4 ,a part of extensive picnic area looking northwest4 ,,the ,,geology ,,of ,d4,a4,r4 ,,state ,,park ,,mt4 ,,philo ,,state ,,forest ,,park ,,sand ,,bar ,,state ,,park ,by ,,harry ,w4 ,,dodge1 ,,jr4 ,,vermont ,,geological ,,survey ,,charles ,g4 ,,doll1 ,state ,geologist ,,department ,,of ,,forests ,,and ,,parks ,,robert ,b4 ,,williams1 ,commissioner ,,department ,,of ,,water ,,resources ,montpelier1 ,vermont #aifi ,illustration3 ,fig4 #a4 ,index ,map4 ,,sandbar ,,state ,,park ,,mt4 ,,philo ,,state ,,park ,,button ,,bay ,,state ,,park ,d4,a4,r4 ,,state ,,park ,,lake ,,champlain ,milton ,burlington ,shelburne ,falls ,hinesburg ,vergennes ,bristol ,port ,henry ,champlain ,bridge ,middlebury ,crown ,point ,shoreham ,,index ,,map ,illustration3 ,fig4 #a;a4 ,surface of marine terrace at ,d4,a4,r4 ,state ,park4 ,immediately to the left of shelter the land rises to a second terrace4 ,illustration3 ,fig4 #b4 ,view northwest along park beach4 ,illustrates dip of rocks toward northwest2 strike1 northeast4 ,,the ,,geology ,,of ,d4,a4,r4 ,,state ,,park ,,introduction ,d4,a4,r4 ,state ,park is located in western ,vermont on ,state ,highway #ag1 approximately #a mile north of ,lake ,champlain 7toll7 ,bridge 7see map1 ,fig4 #a74 ,the park1 which fronts on ,lake ,champlain1 contains undeveloped acres on the east side of the ,highway4 ,tenting1 leanto camping1 picnicking and swimming are adequately provided for during the summer months4 ,this park1 more than most others1 not only awakens the visitor's curiosity about the past history of the ,earth1 but satisfies it4 ,the story of an ancient sea and the life which existed in it can be read from the rocks exposed in ,d4,a4,r4 ,state ,park4 ,you can read this story for yourselves4 ,this ,pamphlet is designed as an aid to a more complete understanding of the observations which you make4 8,reading the rock record0 is not difficult1 but the geologist does have the advantage of possessing a certain trained scientific approach to these problems4 ,this method of approach1 the 8tools of the trade10 will now be passed on to you4 ,,the ,,geology ,,of ,,the ,,park ,the park beach is the ideal place to study the rocks of the park1 for here the rocks are best exposed and can be easily examined at close range4 ,the attitude of the rock layers can be seen on a walk down the ramp4 ,by attitude is meant their relationship to an imaginary horizontal plane1 which for our purposes is the level of the lake4 ,are the rock layers parallel to the surface of ,lake ,champlain or do they slant or dip into it8 ,if the layers were parallel to the surface they would not 8dip40 ,the dip of the park strata 7layers7 is seen in ,figure #b4 ,dip is expressed in the number of degrees down from the horizontal and here the dip is toward the west and is measured to be between #h and #aa degrees4 ,the dip is always measured perpendicular to an imaginary horizontal line on a rock layer called a 8strike line40 ,the average 8strike10 or compass direction of the 8strike line0 is #bb degrees east of north4#a ,sedimentary rocks#b crop out on the park beach4 ,these were originally lime mud resting on the sea bottom4 ,under continued pressure from the overlying sediments resulting from continued deposition and burial1 the muds were slowly compacted and cemented into the hard limestones and limy shales which we see today4 ,the many layers of rock were then tilted4 ,tilted layers tell the geologist of giant earth movements which took place since their formation4 ,the story of these movements will be developed later in this pamphlet4 ,as you look at the tilted rock layers from the ramp1 can you tell which layers are the oldest1 that is1 those first deposited as lime muds on the sea bottom8 ,a basic geologic law1 the ,law of ,superposition1 states that if a series of sedimentary layers have not been overturned1 the oldest is on the bottom and the youngest on top4 ,assuming that the layers which you are looking at have not been overturned1 those on your left 7south7 are the oldest and those on your right 7north7 the youngest4 ,looking at ,figure #b1 taken from the ramp-bottom toward the north1 the layers in the foreground are older than those in the distance4 ,let us take a close look at the individual layers of rock and delve deeper into the story that they have to tell4 ,illustration3 ,fig4 #c4 ,block diagram illustrating dip and strike4 ,,strike ,,direction ,,rock ,,layer ,,surface 7,,plane7 ,,lake ,,level ,,horizontal ,,dip ,,rock ,,layer ,search the top of a few layers and you will notice many shell and other animal impressions4 ,do they represent animals which lived hundreds of millions of years ago or were they washed onto these rocks from present-day ,lake ,champlain8 ,if you try to make a collection of the shell impressions you will see that they are a part of the rock and therefore must represent remains of animals that were buried in the ancient lime muds4 ,these preserved remains#c are called fossils4 ,the geologist who specializes in the study of fossils is called a paleontologist4 ,you may ask1 8,what can fossils tell me about the past80 ,in the first place1 fossils tell us at what time in the past the sediments in which they are found were deposited4 ,in this way1 the relative age#d of the rock layers found in the ,park can be learned4 ,secondly1 the environment or surroundings in which these ancient sediments were deposited can be reconstructed from the types of fossils contained within them4 ,certain animals living today are quite similar to those in the ,park rocks and their environment in today's sea can be used to reconstruct the environment of animals which lived in the past4 ,the characteristics of the rocks and their relation to adjacent rocks are considered in any reconstruction of past environment4 ,in the third place1 the study of fossils is a mainstay of the theory of evolution4 ,that is to say1 changes in fossil forms collected from groups of successively younger rock layers document the theory that life has evolved little by little since its first appearance on ,earth4 ,finally1 it should be mentioned that some animals found as fossils are not living today and have not lived1 to the best of our knowledge1 for millions of years4 ,why did these forms of life die out8 ,what set of circumstances led to their extinction8 ,the answers to these questions are not easy to find and they are highly speculative4 ,illustration3 ,fig4 #d4 ,standard ,geologic ,time ,scale4 ,,geologic ,,time ,,era ,,years ,,ago ,,periods ,,events ,,cenozoic #gj1jjj1jjj ,,cenozoic ,,man 7#a ,,million7 ,,mesozoic #abe1jjj1jjj ,,cretaceous ,,end ,,of ,,dinosaurs #afe1jjj1jjj ,,jurassic ,,first ,,bird #bjj1jjj1jjj ,,triassic ,,first ,,dinosaur ,,paleozoic #bcj1jjj1jjj ,,permian ,,end ,,of ,,trilobites #bfj1jjj1jjj ,,pennsylvanian #bij1jjj1jjj ,,mississippian #ccj1jjj1jjj ,,devonian #cfj1jjj1jjj ,,silurian #dbj1jjj1jjj ,,ordovician ,,rocks ,,of ,d4,a4,r4 ,,state ,,park #ejj1jjj1jjj ,,cambrian ,,beginning ,,of ,,fossil ,,record #a ,,billion #b ,,billion #c ,,billion #d ,,billion ,,precambrian ,,the ,,fossils ,many groups of invertebrates are represented in the fossils of ,d4,a4,r4 ,state ,park4 ,plate #a will help you to identify these fossils4 ,the name1 phylum 7major group7 and age of each fossil are provided in the explanation of the plate4 ,the following paragraphs describe each phylum represented in the ,park rocks4 ,illustration3 ,plate #a4 ,typical fossils found in the ,glens ,falls ,limestone4 ,arthropods4 ,d4,a4,r4 ,state ,park rocks contain trilobites with the following imposing names3 ,cryptolithus tesselatus 7crip-toe-,,lith-us tessell-,,ah-tus#e71 ,isotelus gigas 7ice-so-,,tell-us ,,gig-us7 and ,flexicalymene senaria 7flex-eye-cal-ah-,mean-ee sen-,,area74 ,these fossils are figured on ,plate #a1 #a-;,a1 ,b1 ,c1 ,d2 #b2 #c4 ,within the ,park ,cryptolithus tesselatus is very common wherever fossils occur4 ,generally only the cephalon or head portion of this trilobite is preserved4 ,the cephalon is easily recognized by three concentric rows of pits arranged around the brim4 ,cryptolithus is an excellent index fossil#f for the ,park rocks4 ,the arthropod phylum is characterized by animals with jointed legs1 segmented bodies and a jointed outer armour of chitin4#g ,for examples1 the crabs1 lobsters1 spiders1 scorpions and insects are arthropods4 ,trilobites appear early in the fossil record but they did not survive beyond the ,paleozoic ,era4 ,explanation for ,plate #a 7all drawings are ,x#a unless otherwise indicated7 #a-;,a4 ,cryptolithus tesselatus1 ,arthropod 7,trilobite71 ,middle ,ordovician 7,trenton ,stage74 ,front view of the ,cephalon or head4 7,x#b7 #a-;,b4 ,cryptolithus tesselatus1 ,arthropod 7,trilobite71 ,middle ,ordovician 7,trenton ,stage74 ,oblique front-lateral view of the ,cephalon4 7,x#b7 #a-;,c4 ,cryptolithus tesselatus1 ,arthropod 7,trilobite71 ,middle ,ordovician 7,trenton ,stage74 ,top view of the ,cephalon4 7,x#b7 #a-;,d4 ,cryptolithus tesselatus1 ,arthropod 7,trilobite71 ,middle ,ordovician 7,trenton ,stage74 ,side view of the ,cephalon4 7,x#b7 #b4 ,isotelus gigas1 ,arthropod 7,trilobite71 ,middle ,ordovician4 ,top view of specimen4 #c4 ,flexicalymene1 ,arthropod 7,trilobite71 ,ordovician to ,silurian4 ,top view of an enrolled specimen4 #d-;,a4 ,dinorthis pectinella1 ,brachiopod1 ,middle ,ordovician 7,trenton ,stage74 ,exterior view of the brachial valve4 #d-;,b4 ,dinorthis pectinella1 ,brachiopod1 ,middle ,ordovician 7,trenton ,stage74 ,exterior view of the pedicle valve4 #e4 ,reuschella edsoni1 ,brachiopod1 ,middle ,ordovician4 ,exterior view of the pedicle valve4 #f4 ,lingula1 ,brachiopod1 ,ordovician to ,recent4 #g-;,a4 ,prasopora1 ,bryozoan1 ,ordovician4 ,top view4 7,x#j4e7 #g-;,b4 ,prasopora1 ,bryozoan1 ,ordovician4 ,side view4 7,x#j4e7 #g-;,c4 ,prasopora1 ,bryozoan1 ,ordovician4 ,vertical thin section showing the nature and growth of part of a bryozoan colony4 7,x#ah7 #h4 ,bryozoan1 8twig-like0 type1 ,ordovician to ,devonian4 #i4 ,sowerbyella1 ,brachiopod1 ,middle and ,upper ,ordovician4 ,exterior view of brachial valve4 7,x#b7 #aj4 ,rafinesquina1 ,brachiopod1 ,middle and ,upper ,ordovician4 ,exterior view of the pedicle valve4 #aa4 ,platystrophia trentonensis1 ,brachiopod1 ,middle ,ordovician 7,trenton ,stage74 ,anterior or front view4 #ab4 ,hesperorthis tricenaria1 ,brachiopod1 ,middle ,ordovician 7,black ,river and ,trenton ,stage74 ,interior view of the pedicle valve4 ,illustration3 ,fig4 #e4 ,the surface of a layer or bed of ,glens ,falls ,limestone4 ,pen points to a colonial ,bryozoan ,prasopora 8head40 ,these 8heads0 are very common just south or to your left if walking down the ramp4 ,brachiopods4 ,brachiopods are abundant in the ,park rocks 7see ,plate #a1 #d;,a1 ,b2 #e2 #f2 #i2 #aj2 #aa2 #ab74 ,these invertebrates are small marine animals which generally live in waters no deeper than #fjj feet4 ,the two valves of their shell are joined at the back 7posterior7 end of the body along a hingeline of interlocking teeth and sockets4 ,the shell of the brachiopod is opened or shut by muscles attached to the inside of each valve4 ,brachiopods are found in the oldest rocks containing definite and abundant fossils4 ,brachiopods are still living today4 ,bryozoans4 ,bryozoans or 8moss animals0 are very small marine animals which live in colonies4 ,the bryozoans construct their mutual home or colony of lime which is commonly preserved for the fossil record4 ,large colonies of the fossil ,prasopora 7prah-sop-,,or-ah7 are commonly seen on the weathered surfaces of many of the rock layers in the ,park 7see ,plate #a2 #g;,a1 ,b1 ,c2 #h and ,figure #e74 ,individuals of one genus common here1 can be recognized by their chocolate drop shapes4 ,bryozoans first appear in lower ,paleozoic rocks and are still living today in clear well-circulated shallow to deep marine water4 ,considering all of the fossils found in the ,park rocks1 the past environment is thought to have been a relatively shallow and warm sea4 ,illustration3 ,fig4 #f4 ,this photograph shows the typical thickness of the ,glens ,falls ,limestone beds in the ,park area4 ,note the massive nature of the limestone bed4 ,the #e-;inch pen in the center of the picture is for scale4 ,illustration3 ,fig4 #g4 ,sections illustrating the geologic history of ,d4,a4,r4 ,state ,park4 ,,the ,,rocks ,,and ,,their ,,history ,approximately #ge vertical feet of the ,glens ,falls ,limestone occur along the ,park beach4 ,the rocks are black#h or blue-black on a fresh surface1 gray or grayish-white on a surface which has been exposed to the weather4 ,most of the individual beds or layers are #e to #g inches thick 7see ,fig4 #f7 with the thickest being just under #e feet4 ,the beds are separated by thin 8partings0 of rock1 many of which contain abundant fossils4 ,the beds consist of massive limestone1 shaly limestone or limy shale2 the partings are generally limy shale or shaly limestone4 ,explanation for ,figure #g #a4 ,glens ,falls and younger sediments were deposited on the ,ordovician sea floor4 #b4 ,sediments hardened into ,glens ,falls ,limestone and younger rocks4 #c4 ,rocks were tilted during the late ,ordovician ,taconic ,disturbance and the younger rocks and part of the ,glens ,falls ,limestone were removed by erosion4 ,erosion continued for some #cej million years4 #d4 ,during the ,pleistocene ,epoch1 which started some #a million years ago1 glacial ice overrode the beveled layers of the ,glens ,falls ,limestone4 ,hard rocks frozen to the underside of the glacial ice produced scratches or striations in the exposed layers of the ,glens ,falls ,limestone4 #e4 ,glacial lakes ,vermont form as the glaciers retreat northward4 ,in between the glacial lakes ,vermont and present ,lake ,champlain1 marine waters flooded the valley and formed an arm of the ,atlantic ,ocean4 ,clay1 silt1 sand and gravel were deposited on glaciated ,glens ,falls ,limestone 7,fig4 #a;a74 #f4 ,present-day ,lake ,champlain formed when relatively greater uplift in the north dammed the ,champlain valley4 ,the rock types found in the ,park lead to certain conclusions regarding the environment which existed during their formation4 ,most of the rocks are composed of lime 7limestone7 or a mixture of lime1 fine sand and mud 7limy shale or shaly limestone74 ,the mineral pyrite 7,fe,s7 is present in many of the rocks4 ,most of the rocks contain abundant amounts of organic matter4 ,the sediments which make up these rocks were carried to the ,ordovician sea by streams flowing primarily from the east4 ,as these streams entered the quiet sea waters the larger followed by the smaller particles began to settle to the bottom4 ,lime was slowly precipitated from the warm sea water and pyrite formed under stagnant bottom conditions4 ,organic material accumulated on the bottom and intermixed with the sediments4 ,the poor life-sustaining qualities of much of the bottom waters prevented rapid or complete bacterial action on the accumulated debris and the sediments remained 8organic black0 in color4 ,slowly1 as the weight of overlying sediments increased1 the lower layers were compacted and cemented into the hard limestone and shale which we see today4 ,the tilt or dip of the ,park rocks resulted from subsequent earth movements4 ,when were these rocks tilted8 ,from the evidence presented in the ,park all that can be said is that they were tilted sometime after hardening and before the ,pleistocene glaciers overrode the region during quite recent times 7at least #aj1jjj years ago74 ,thus1 there are some #cej million years of rock record missing in the ,park4 ,can we tell what happened during these 8missing0 years through a study of only the ,park rocks8 ,the answer to this question is partially 8yes10 but we must look to the work done in adjacent areas for a more complete story4 ,the mere fact that there are no rocks representing these millions of years tells us that the sea had withdrawn from the area and that the previously deposited rocks were undergoing erosion during most or all of the missing rock gap 7the time not represented by rocks74 ,information from adjacent areas1 however1 tells us that the ,park rocks were tilted during the ,taconic ,disturbance which occurred during the final stages of the ,ordovician ,period4 ,east of the ,park1 ,taconic earth movements are more dramatically exhibited4 ,the rocks are tilted even more than in the ,park and are broken by faults or cracks in the earth's crust4 ,some of these faults1 known as thrust faults1 positioned giant slabs of rock far from their original locations and placed older on top of younger rocks4 ,following these earth movements there occurred a long period of erosion4 ,many of the rock layers were stripped off and carried piece by piece by rivers to other regions4 ,hundreds of millions of years passed and then1 less than one million years ago the great glacial ice sheets slowly advanced southward over the ,park area4 ,pieces of hard rock frozen to the underside of the ice sheets scratched and scraped the rock surfaces leaving these scratches or striations for us to see today 7near the northern end of the ,park beach these striations are common on the outcropping rock74 ,the retreating glaciers created a series of lakes in which clay1 silt1 sand and gravel were deposited4 ,today these sediments are found resting on the beveled edges of the ,park rocks4 ,present-day ,lake ,champlain owes its existence to a general uplift of the earth's surface1 greater in the north than in the south1 perhaps due to the removal of the heavy glacial ice sheet from the area4 ,the greater uplift in the north dammed the ,champlain valley which slowly filled with water4 ,for a diagrammatic picture of the geologic history of ,d4,a4,r4 ,state ,park1 see ,figure #g4 ,,suggested ,,reading ,beerbower1 ,j4 ,r41 #aifj1 ,search for the ,past1 ,prentice-,hall1 ,englewood ,cliffs1 ,n4,j4 ,collinson1 ,c4 ,c41 #aiei1 ,guide for beginning fossil hunters1 ,educational ,series #d1 ,illinois ,state ,geological ,survey1 ,urbana1 ,ill4 ,dunbar1 ,c4 ,o41 #aiei1 ,historical geology1 ,john ,wiley and ,sons1 ,new ,york4 ,fenton1 ,c4 ,l41 #aicg1 ,life long ago1 ,the ,john ,day ,co41 ,new ,york4 ,goldring1 ,winifred1 #aica1 ,handbook of paleontology for beginners and amateurs1 part #b1 ,handbook #i1 ,new ,york ,state ,museum1 ,albany1 ,new ,york4 ---- ----1 #aiej1 ,handbook of paleontology for beginners and amateurs1 part #a1 ,handbook #i1 #bnd ,edition1 ,new ,york ,state ,museum1 ,albany1 ,new ,york4 ,moore1 ,r4 ,c41 #aieh1 ,introduction to historical geology1 #bnd ,edition1 ,mc,graw-,hill ,book ,co41 ,new ,york4 ,shimer1 ,h4 ,w41 #aicc1 ,introduction to study of fossils1 ,the ,macmillan ,co41 ,new ,york4 ,simpson1 ,g4 ,g41 #aiec1 ,life of the past1 ,yale ,university ,press1 ,new ,haven1 ,conn4 ,stokes1 ,w4 ,l41 #aifj1 ,essentials of earth history1 ,prentice-,hall1 ,inc41 ,englewood ,cliffs1 ,n4,j4 ,welby1 ,c4 ,w41 #aifa1 ,bedrock geology of the ,central ,champlain ,valley of ,vermont1 ,vermont ,geological ,survey ,bull4 #ad4 ---- ----1 #aifb1 ,paleontology of the ,champlain ,basin in ,vermont1 ,vermont ,geological ,survey ,special ,publication #a4 ,illustration3 ,fig4 #g;a4 ,view south from ,mt4 ,philo ,overlook4 ,shellhouse and ,buck mountains in the distance4 ,illustration3 ,fig4 #h4 ,view looking north at western ,overlook in the summit area of ,mt4 ,philo4 ,note ,monkton ,quartzite layers which are dipping toward the northeast4 ,,the ,,geology ,,of ,,mt4 ,,philo ,,state ,,forest ,,park ,,introduction ,mt4 ,philo ,state ,forest ,park1 consisting of some #afj acres1 is located about #ae miles south of ,burlington and #a mile east of ,u4,s4 ,route #g 7see map1 ,fig4 #a74 ,this park is noted for its scenic views1 especially of the broad ,champlain ,valley and the rugged ,adirondack ,mountains beyond 7see cover picture and ,fig4 #g;a74 ,from a #df-;foot high observation tower a panoramic view is easily gained4 ,picnic facilities1 including stone fireplaces1 fuel wood1 piped spring water and sanitary facilities are available4 ,a large rustic lodge with porch and portico provides protection from sudden showers4 ,tenting on the top of ,mt4 ,philo is not allowed4 ,,the ,,geology ,,of ,,the ,,park ,the ,rocks ,the rocks of the ,park which will probably first attract your attention are those exposed at the main western ,overlook which is located in the summit area4 ,this ,overlook is found just northwest of the ,park lodge 7see ,fig4 #h74 ,these rocks are light to dark red or purplish in color1 are primarily quartzite with minor dolostone#i dipping approximately #ce degrees to the northeast 7for an explanation of dip1 see ,fig4 #c and text of ,d4,a4,r4 ,state ,park1 page #f7 and striking toward the northwest 7for an explanation of strike1 see immediately preceding reference74 ,a closer look at this ,monkton ,quartzite outcrop shows that it is made up of several layers of rock 7see ,fig4 #h74 ,these layers1 strata1 or beds are not all of the same thickness1 but are generally from #a inch to #a foot thick4 ,if an individual layer is traced over the extent of the outcrop1 it is found that its thickness remains about the same throughout4 ,it is therefore said to be regularly bedded4 ,thin laminations of dark red shale are abundant and commonly define individual layers4 ,a magnified look at a specimen of this quartzite1 under a hand lens1 shows that it is composed of fine to coarse fragments of quartz4 ,some of these fragments have rounded edges1 but others are quite angular4 ,the spaces between the fragments are filled with silica 7quartz74 ,therefore1 the rock is said to possess a silica cement4 ,in many places where this ,monkton ,quartzite has been studied1 features attesting to a shallow water origin have been found4 ,among these features are mud cracks1 which form under alternating wet and dry conditions2 ripple marks1 which are usually found only on shallow water bottoms2 and cross-bedding1 which commonly forms in shallow water areas4 ,the ,monkton ,quartzite underlies approximately a third of the ,park 7see ,geologic map1 ,fig4 #i74 ,this quartzite is between #bej and #cjj feet thick on ,mt4 ,philo2 however1 the lower #ej feet or so consist predominantly of white quartzite interbedded with dolostone4 ,the age of the ,monkton ,quartzite is considered to be ,lower ,cambrian 7see ,standard ,geologic ,time ,scale1 ,fig4 #d74 ,illustration3 ,fig4 #i4 ,geologic ,map of ,mt4 ,philo ,state ,forest ,park 7after ,c4 ,w4 ,welby4 #aifa74 ,because ,ogf and ,oib were not definitely identified by the author of this pamphlet and for the sake of simplicity1 these rock units have not been discussed in the text of the pamphlet4 ,some dip and strike symbols have been added to ,welby's original map4 ,,legend ,,upper ,,middle ,,ordovician ,oib ,iberville shale ,osp ,stony ,point shale ,ogf ,glens ,falls limestone ,,lower ,,cambrian ,cm ,monkton quartzite ,park roads ,other roads ,contour line ,approximate park boundary ,dip and strike symbol4 ,layers dip #ba toward ,n4,e4 ,approximate contact of rock units4 ,surface trace of thrust 7low-angle7 fault1 carat on upthrown side ,inferred trace of thrust 7low-angle7 fault1 carat on upthrown side ,surface trace of high-angle fault ,dip and strike of cleavage ,observation tower ,a second type of rock is exposed in the south bank of the exit road approximately #j4g miles from the summit area4 ,this is the black#aj to bluish-black ,stony ,point ,shale 7see ,fig4 #aj71 which underlies the ,monkton quartzite4 ,this shale1 or hardened limy mud1 is thinbedded and shows abundant cleavage#aa parallel to the layers or beds4 ,at this outcrop the layers strike to the northeast and dip #bj to #dj degrees toward the southeast4 ,the dip and strike of the ,monkton ,quartzite 7see above7 is not similar to the dip and strike of the underlying ,stony ,point ,shale4 ,it follows1 that the layers of the ,monkton ,quartzite are not parallel to those of the ,stony ,point ,shale4 ,illustration3 ,fig4 #aj4 ,view looking south of cut-bank1 south side of exit road1 about #j4g miles down from the summit parking area4 ,here the layers dip #bj to #dj degrees toward the southeast and strike in a northeast direction4 ,note that the shale is thin-bedded and contains numerous cleavage planes parallel to the layering4 ,the handle of the geologic pick is about #a foot long4 ,the fact that these two units are not parallel could mean that the ,stony ,point ,shale was deposited1 hardened into rock1 uplifted1 folded and eroded1 all prior to the deposition of the ,monkton ,quartzite4 ,but1 first1 what is the age of the underlying ,stony ,point ,shale8 ,if the story is as listed above1 the ,stony ,point ,shale must be older#ab than the overlying ,monkton ,quartzite4 ,from the fossil animal remains found in the ,stony ,point ,shale1 geologists have dated the ,stony ,point ,shale as upper middle ,ordovician 7see ,standard ,geologic ,time ,scale1 ,fig4 #d74 ,and so1 here we have older rocks 7,lower ,cambrian7 resting on younger 7upper middle ,ordovician74 ,illustration3 ,fig4 #aa4 ,view of ,mt4 ,philo1 looking toward the northeast4 ,the black line approximates the position of the thrust fault4 ,the ,monkton ,quartzite1 which is above the line1 was thrust westward over the ,stony ,point ,shale 7note the arrow74 ,line ,a-,b1 ,fig4 #i1 approximates the section4 ,structural ,geology ,how can we explain this inverted order of rock units8 ,the geologic evidence presented in the ,park does not indicate that folding of the rocks was responsible4 ,from the surface distribution of the two rock types 7see ,geologic map1 ,fig4 #i7 and the nature of their contact with each other1 a fault relation is envisioned1 in which older rocks were thrust westward over the younger and thus to rest upon them 7see ,fig4 #aa 74 ,we know the ages of both rock units involved in this thrust fault but what is the geologic age of the actual thrust movement8 ,both the ,stony ,point ,shale and the ,monkton ,quartzite were hard rock when this thrusting took place1 therefore1 the thrusting would have occurred later than upper middle ,ordovician time1 but before late ,silurian time4 ,two other fault systems are recognized in or near the ,park 7see ,geologic map1 ,fig4 #i74 ,they are high angle#ac faults which formed later than the thrust fault1 but still preceding late ,silurian time4 ,the ,iberville ,shale 7this is not described in the section on 8,the ,rocks10 but is seen on the ,geologic map1 ,fig4 #i71 which is questionably exposed on the south side of ,mt4 ,philo1 would be the youngest rock found in the ,park4 ,this shale is about #cij million years old4 ,the most recent faulting took place no later than about #cdj million years ago4 ,there are no rocks in the ,park which give us any positive geological clues to the ,park's history from the last episode of faulting to the ,pleistocene glaciers less than #a million years ago4 ,however1 the fact that rocks representing this interval of time are not present does indicate that the area was above water during most of these #cci million years 7this number of years is very approximate74 ,if any rocks were deposited during this 8rock-gap0 period1 they have since been washed away4 ,the ,pleistocene ,deposits ,beginning between #fj1jjj and #gj1jjj years ago two glacial advances and retreats took place in the ,champlain ,valley4 ,this was during the most recent or the ,wisconsin ,stage of the ,pleistocene ,epoch4 ,scratches or striations were cut into the overridden rock by rock debris carried along at the base of the ice as it advanced 7note the arrow in 78br07 area at overlook in ,fig4 #ab2 this shows striation orientation1 therefore1 the direction in which the glacier advanced74 ,the glacial sediments found on ,mt4 ,philo were deposited during the final retreat of glacial ice1 which took place from #aa1jjj to #ab1jjj years ago4 ,most of the ,park is covered with these glacial deposits and by more recent soils4 ,most of the glacial deposits found on ,mt4 ,philo are classified as glacial till#ad 7see ,map of ,glacial ,deposits1 ,fig4 #ab71 but other glacial deposits are also mapped4 ,a kame#ae 7designated 8,k0 in ,fig4 #ab7 is a glacial feature found in the southern part of the ,park4 ,illustration3 ,fig4 #ab4 ,map of the ,pleistocene deposits of ,mt4 ,philo ,state ,forest ,park 7after ,d4 ,p4 ,stewart1 #aifa74 ,,legend bc ,boulder strewn lake sediments bgm ,marine beach gravel bg ,beach gravel ps ,pebbly sand ls ,lake sand t ,till k ,kame br ,bedrock ,park roads ,other roads ,with the slow retreat of the glacial ice front from the ,mt4 ,philo region1 deposits were left which indicate that a series of lakes formed in front of the wasting ice mass4 ,there is also evidence just west of ,mt4 ,philo 7see 8bgm0 in ,fig4 #ab7 which indicates that just prior to the formation of present-day ,lake ,champlain1 an arm of the ,atlantic ,ocean reached into the ,champlain ,valley from the ,st4 ,lawrence ,river region4 ,lake-beach gravels 7designated 8bg0 in ,fig4 #ab7 are found on both the east and west slopes of ,mt4 ,philo4 ,the interesting fact about these beach gravels is that they occur almost #ejj feet above the present-day level of ,lake ,champlain4 ,lake sand 7designated 8ls0 in ,fig4 #ab7 is found some #dej feet above ,lake ,champlain4 ,this means that during a good portion of its recent geologic history1 ,mt4 ,philo was an island surrounded by lake water4 ,from the distribution of marine beach gravel 7designated 8bgm0 in ,fig4 #ab71 it appears that the invasion of sea water from the ,st4 ,lawrence region did not isolate ,mt4 ,philo as an island4 ,the complete story of the lake series is still not known1 but1 for the most up-to-date treatment of this subject see ,d4 ,p4 ,stewart's paper entitled 8,the glacial geology of ,vermont03 ,vermont ,geological ,survey ,bulletin #ai 7#aifa74 ,suggested also is ,c4 ,h4 ,chapman's article entitled 8,late glacial and postglacial history of the ,champlain valley0 in the ,american ,journal of ,science1 #eth series1 volume #cd1 pages #hi-abd 7#aicg74 ,looking out over the ,champlain lowlands from the summit of ,mt4 ,philo leaves little doubt in the visitor's mind as to the prior existence of lakes which surrounded ,mt4 ,philo in the not too distant past 7see ,cover picture74 ,summary of the ,geologic ,history ,during lower ,cambrian time1 the ,monkton ,quartzite and dolostone followed by the ,winooski ,dolostone 7not seen in the ,park7 were deposited east of ,mt4 ,philo ,state ,forest ,park4 ,during late ,cambrian and early ,ordovician1 thick dolostones were deposited from the sea water which covered the ,mt4 ,philo area 7not seen at the surface in the ,park74 ,during middle ,ordovician time1 a series of shale1 calcareous shale and limestone was deposited from the sea water4 ,then1 sometime between the beginning of late ,ordovician and late ,silurian time1 the eastern lower ,cambrian sequence was thrust westward over the middle ,ordovician rocks4 ,this low-angle thrusting was succeeded by high angle faulting4 ,the ,park rocks were subjected to weathering and erosion for over #cjj million years or until glaciers advanced over the area less than #fj1jjj to #gj1jjj years ago4 ,advancing glaciers scoured the rock2 retreating or wasting glacial ice left deposits of clay1 sand and gravel in the ,park4 ,a series of lakes formed south of the northward wasting glacial ice and deposits of beach-gravel and lake-sand formed along the slopes of ,mt4 ,philo1 which was then an island4 ,an arm of the sea next advanced southward into the ,champlain ,valley leaving marine beach-gravels just west of ,mt4 ,philo4 ,the marine waters retreated and present-day ,lake ,champlain came into existence4 ,the formation of the present soil cover and the deposition of recent alluvium from presently flowing rivers and streams concludes this brief summary of the ,park's geologic history4 ,,suggested ,,reading 7in addition to the general references listed for ,d4,a4,r4 ,state ,park7 ,cady1 ,w4 ,m41 #aide1 ,stratigraphy and structure of west-central ,vermont1 ,geological ,society of ,america ,bulletin1 volume #ef1 pages #eae-ehh4 ,chapman1 ,c4 ,h41 #aicg1 ,the glacial and postglacial history of the ,champlain valley1 ,american ,journal of ,science1 #eth series1 volume #cd1 pages #hi-abd4 ,stewart1 ,david ,p41 #aifa1 ,the glacial geology of ,vermont1 ,vermont ,geological ,survey ,bull4 #ai4 ,stewart1 ,david ,p4 and ,paul ,mac,clintock1 #aifi1 ,the ,surficial ,geology and ,pleistocene ,history of ,vermont1 ,vermont ,geological ,survey ,bull4 #ca 7in press74 ,welby1 ,c4 ,w41 #aifa1 ,bedrock geology of the ,central ,champlain ,valley of ,vermont1 ,vermont ,geological ,survey ,bull4 #ad4 ,illustration3 ,fig4 #ab;a4 ,over a typical ,grand ,isle split-rail fence at ,sand ,bar ,state ,park4 ,illustration3 ,fig4 #ac4 ,a portion of the beach at ,sand ,bar ,state ,park looking east4 ,the escarpment in the left distance marks the trace of the ,champlain thrust fault4 ,,the ,,geology ,,of ,,sand ,,bar ,,state ,,park ,,introduction ,sand ,bar ,state ,park is located in northwestern ,vermont on ,u4,s4 ,route #b1 approximately #ad miles north of ,burlington and near the east approach to ,sand ,bar ,bridge which leads to ,south ,hero ,island in ,lake ,champlain 7see map1 ,fig4 #a74 ,tenting1 picnicking and swimming are the ,parks main attractions 7,fig4 #ab;a74 ,the swimming beach is on the north side of ,u4,s4 ,route #b and fronts on ,lake ,champlain4 ,its shallowness makes the beach safe for children 7,fig4 #ac74 ,the tenting facilities are located on the south side of ,u4,s4 ,route #b on a south-facing shoreline4 ,,the ,,geology ,,of ,,the ,,park ,the geologic history of ,sand ,bar ,state ,park is recent1 geologically speaking1 especially when compared with that of the other ,parks treated in this pamphlet4 ,the sediments of the park are blue and brown clay which were deposited throughout the ,champlain ,valley less than #aj1jjj years ago4 ,this clay1 which can be seen in many places along the bathing beach1 was deposited from marine waters which flooded the ,champlain ,valley just prior to the formation of present-day ,lake ,champlain4 ,no bedrock crops out in ,sand ,bar ,state ,park4 ,the blue clay is covered with deposits brought downstream by the ,lamoille ,river during very recent times and deposited as a delta#af into ,lake ,champlain4 ,this delta has shifted its distributary channels frequently and continues to grow southwestwardly into ,lake ,champlain4 ,much of the finer material 7sand7 brought into ,lake ,champlain by the ,lamoille ,river has been shifted and concentrated by lake currents into ridges or bars2 one sand bar stretches to ,south ,hero ,island and forms the foundation for the causeway named ,sand ,bar ,bridge4 ,prior to the building of ,sand ,bar ,bridge 7causeway was started in #ahdi1 opened to travel on ,december #e1 #ahej71 this sand bar was fordable and was used as a link between ,south ,hero ,island and the mainland4 ,most of the sand now found north of the ,park bathing beach and which is responsible for the extensive 8shallows0 in the swimming area1 was supplied by the now abandoned northern channel of the ,lamoille ,river4 ,it is interesting to note that most of the sand now seen on the bathing beach has been imported from nearby areas of ,vermont4 ,since the northern distributary channel of the ,lamoille ,river is no longer supplying sand1 and sand from the active southern channel cannot work its way northward because of the ,sand ,bar ,bridge causeway1 there is a lack of sand for the beach4 ,the extensive swamp areas near the east end of ,sand ,bar ,bridge are a wildlife sanctuary4 ,the north-trending prominent escarpment east of the ,park marks the trace of the ,champlain thrust fault 7,fig4 #ac74 ,in a quarry at the east end of ,sand ,bar ,bridge may be seen the fault contact between the younger1 ,middle ,ordovician1 ,stony ,point ,formation1 and the older1 ,lower ,cambrian1 ,dunham ,dolomite4 ,,suggested ,,reading ,erwin1 ,r4 ,b41 #aieg1 ,the ,geology of the ,limestone of ,isle ,la ,motte and ,south ,hero ,island1 ,vermont1 ,vermont ,geological ,survey1 ,bull4 #i4 ,stone1 ,s4 ,w4 and ,dennis1 ,j4 ,g41 #aifd1 ,the ,geology of the ,milton ,quadrangle1 ,vermont1 ,vermont ,geological ,survey ,bull4 #bf4 ,additional reports on the geology of ,vermont state parks distributed by the ,vermont ,state ,library1 ,montpelier1 ,vermont #jefjb4 ,the ,geology of ,groton ,state ,forest1 by ,robert ,a4 ,christman1 #aief ,the ,geology of ,mt4 ,mansfield ,state ,forest1 by ,robert ,a4 ,christman1 #aief ,the ,geology of the ,calvin ,coolidge ,state ,forest ,park1 by ,harry ,w4 ,dodge1 ,jr41 #aiei ,geology of ,button ,bay ,state ,park1 by ,harry ,w4 ,dodge1 ,jr41 #aifb ,the ,geology of ,darling ,state ,park1 by ,harry ,w4 ,dodge1 ,jr41 #aifg ,,footnotes #a;,a 8strike0 measurement is expressed as so many degrees east or west of north or south4 ,for a diagram illustrating the dip and strike of a rock layer see ,figure #c4 #b,this is one of the three major rock groups or families4 ,the first consists of igneous rocks1 including granite1 syenite1 and basalt1 which were formed by solidification of molten rock-material4 ,the igneous rocks are ancestors of the other two rock families2 they form over #ij percent of the outer #aj miles of the ,earth's crust4 ,the second family1 consisting of sedimentary or layered rocks including shale1 sandstone and limestone1 is composed of pieces and grains and other materials from all the families of rocks4 ,in addition1 sedimentary rocks are formed also from lime secreted by marine plants and animals or chemically precipitated from sea water1 or by the accumulations of shells4 ,the third family1 metamorphic rocks1 including gneiss1 schist1 slate and marble1 were igneous or sedimentary rocks that have been subjected to heat and pressure in the presence of mineral-forming solutions4 ,metamorphic rocks generally look different from the rocks from which they formed1 because the original minerals of the rock have been changed and reoriented4 #c,the actual remains are usually not preserved in their original state but are represented by molds and casts4 ,picture an ancient sea4 ,the sea bottom mud slowly hardens around a shell4 ,water then seeps through the hardened mud and dissolves the shell leaving an open space where the shell once was4 ,this open space is a mold4 ,if the mold is filled a copy of the original shell is formed4 ,this is called a cast4 #d,the relative rather than the absolute age of the rocks can be determined from a study of their fossil content4 ,these fossils are compared with collections from various places in the world where the standard geologic time scale assigns them a place 7see ,fig4 #d74 ,the ,park rocks were deposited during the ,ordovician ,period4 ,how is a standard geologic time scale put together8 ,several geologists first worked out the sequences of rocks according to the ,law of ,superposition in ,great ,britain and neighboring parts of ,europe4 ,when systematic collections of fossils were made from these layers and arranged according to age it was found that certain fossils occurring in rocks in distant areas were identical and occupied the same relative age position4 ,these fossils were considered to be of the same relative age4 ,fossils found in the ,park can be compared with these reference fossils and a relative geologic age can be assigned to them4 ,absolute ages can be determined in some cases by the use of rates of decay of radioactive elements and in general these ages agree with the relative ages derived through the use of fossils4 #e,the capitalized syllable is the accented syllable4 #f;,an index fossil is used to date the rocks in which it occurs4 ,a good index fossil must be abundant1 widespread and easily recognized4 ,its vertical range is restricted to a small number of rock layers1 therefore the geological span of life of a good index fossil is usually short4 #g;,chitin is a colorless horny substance similar to the material which makes up fingernails4 #h,the black color is due to an abundance of finely divided organic 7plant and animal7 material within the rock4 #i;,a quartzite is either a metamorphic or sedimentary rock consisting of fragments of the mineral quartz 7,si,o7 which are cemented together by silica 7quartz74 ,the combination of quartz fragments held together by quartz cement creates a very hard rock which oftentimes will break across the fragments rather than around them4 ,the quartzites of the ,park area are primarily of a sedimentary origin4 ,for a description of the three major rock groups1 of which the sedimentary and metamorphic groups are two1 see footnote1 ,d4,a4,r4 ,state ,park1 page #f4 ,a dolostone is a sedimentary rock composed of fragmental1 concretionary1 or precipitated dolomite 7a mineral of chemical composition1 ,ca,mg7,,co77 of organic or inorganic origin4 #aj,the black color is due to the inclusion of finely disseminated carbonaceous material 7animal and plant remains7 within the rock4 #aa,this splitting or cleavage was produced after the layers had hardened into rock4 ,the cleavage planes were produced when the rocks were subjected to pressures too great to withstand4 ,in some places these cleavage planes do not parallel the layers4 #ab;,according to the basic geologic law1 the ,law of ,superposition1 younger rocks 7those deposited last7 are always found resting on older rocks 7those deposited before the younger74 ,the only time that this is not true is when either breaks 7faults7 or folds in the earth's crust place the layers in an inverted order1 as in the case here cited4 #ac,the fault plane of a high-angle fault forms a large angle 7generally from #cj to #ij degrees7 at its intersection with an imaginary horizontal plane4 ,the plane of a thrust fault1 or low-angle fault1 forms a small angle 7generally less than #cj degrees7 at its intersection with an imaginary horizontal plane4 #ad,this is the ,burlington till 7,stewart1 #aifa7 and was deposited from the ,burlington ,ice ,lobe during its period of wasting4 ,the till is a hodge-podge mixture of clay1 sand and pebbles and is usually brown in color4 #ae;,a kame is a mound or ridge of poorly sorted 7sometimes well-sorted1 that is1 made up of all the same sized particles7 water deposited materials4 ,most kames are ice-contact features2 that is to say1 the materials which make up the kame were deposited in contact with a glacial ice surface4 ,the ,mt4 ,philo kame may be the filling of an ice-free area during the final melting of the glacial ice4 #af;,delta is the name of the fourth letter of the ,greek alphabet1 the capital form of which is an equilateral triangle4 ,the triangular-shaped tract of land formed by the deposit of river sediment at river mouths is named for the triangular shape of the capital ,greek letter delta4 ,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