Fossil Collecting in Pennsylvania Part 1 of 3

7/29/2019 Fossil Collecting in Pennsylvania Part 1 of 3

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FOSSIL COLLECTPENNSYLVANIA

byDonald M. Hoskins, JonD. Inners, and JohnA . Harper

INTRODUCTIONby Donald M. Hoskins

The Pennsylvania Geological Survey frequently receives requests forinformation on where to collect fossils in the Commonwealth. This booki s intended to supply such information; thus the major portion of thebook i s devoted to a geographic and geologic description o f fossil locali-ties, including lists of the fossils t o be found at each locali ty.

Although knowing the location of fossil-collecting sites i s important,there i s more to fossils than just collecting them. The study sf fossils(paleonto%ogy)s the lifetime work of many scientists. Their work hasgiven answers t o some of the basic questions of the evo lution of li fe andthe world we live in. To have a comprehensive understanding of what fos-sils signify gives the collector a greater appreciation s f the hobby inwhich he i s engaged. To enhance this appreciation, the first portion ofthe book i s devoted t o the significance and uses of fossils as well as thedescription of the major groups s f fossils that one may encounter whenengaged in fossil collecting in Pennsylvania. For those interested in Cur-ther information on paleontology, references are listed near the end ofthe book.

WHAT I S A FOSSIL?Fossils occur in many forms. The footp rin t or burrow of an animal pre-

served in rock i s a fossil; a clam shell preserved in rock i s a fossil; the im-prin t of a leaf in a rock i s a fossil. A fossil i s a n y na tu ra l l y formed recordo f a n im a l or p l a n t l i f e fo u n d in rocks that gives an idea s f the appearanceof the original organism.

Imagine for a moment a common dweller of today's ooceans-theclam. A clam i s composed of two shells (called valves) surrounding afleshy body which contains muscles that open and close the shells. If weexamine the various processes that may affect this clam after i t dies, wewill learn the many ways in which the clam can be preserved as a fossil.


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FOSSIL COLLECT BNC IN PENNSYLVANIA

F e r n

Some examples of fossils.

When the cl am dies, the fleshy parts qalickly decav and disappear ancdthe shells are le ft t o be washed about o n the sea bo tt om or shore Be-cause the muscles tha t he ld them together are gone, the shells frequentlyseparate The shells may be destroyed by currents on th e sea bo ttom , orthey may be buried beneath sediments, w fl ich csnt lnua lly accumulate onthe sea floor Bur ia l by sediments is the f i r s t step in foss i l i za t ion .

7-he sedin ient surrounding the shell may become compacted clnd turninto hard rock, and the shell may be preserved wi th no further changesBut many shells are dissolved by the water In the co mpa cte d sediment,leaving a space that becomes a mold, which preserves all the details otthe shell surface If other mate rial later til ls this space and hardens, thehardened material becomes a cast Both casts and molds are tosslls be-cause, although nothin g of the origi nal shell is left, we can see what thethell loo ke d Bike Since the outside and inside of a shell generdlly are di f -ferent, we call molds and casts ~nterndl ins lde) nd externa l (o i~ t~ id e j ,je-pending on which par t of the shell they represent Mo lds are com mon CISfossils, but casts are relat ive ly rare

M O L D C A S T

Mold and cast of a pelecypod.


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INTRODUCV ION 3I f t h e c l a m she ll escapes be ing d isso lved , i t may be a f fec ted by o the r

processes as the rock around it h a r d e m O n e of these processes is re-p l a c e m e n t , W h e n e x a m i n ed m i c r o s c o p ic a l ly , m o s t r o c k s f o r m e d f r o msediments a re foun d t o c on ta i n m an y ve ry sm a l l po res and spaces. Thepo res and spaces m ay b e i n te rconnec ted and m ay c on ta in wa te r ca r ry i ngd isso lved minera ls . Und er cer ta in con d i t ions , m inera ls ca r r ied by th is wa-t e r w i l l b e s u b s t it u t e d f o r t h e m a t e r i a l of t he she l l , wh i ch i s common lythe minera l ca lc i te , so tha t the she l l is g radua l l y rep laced by m ine ra l ssuch as quar tz o r py r i te .

Some animals, such as insects , possess no hard par ts (ske le ton o r she l l) ;t he i r body cove r i ng cons i s ts o f an o rgan i c compound ca l l ed ch i t i n , ama ter ia l s im i la r t o ou r f i ngerna i ls . These anima ls , whe n bur ied , a re p re -se rved unde r on l y the mos t excep t i ona l c i r cums tances whe reby thech i t i n , t h rough a p rocess c a l l ed d i s t il la t i on , is reduc ed t o a th i n ca rbo nf i lm as the sed imen t is compac ted . Th is f i l m ma y p rese rve ma ny o f th every f ine fea tu res o f these an ima ls .

P lan ts a re usua l l y fou nd as tw o types o f fossi ls . O ne i s t h e i m p r i n t o fleaves, ferns, and seeds that have been carbonized by t h e d i s t i l la t i o nprocess d iscussed abo ve. L imbs, roots , and t runks o f t rees are ma ny t ime spreserved as casts and molds; rare ly , la rge por t ions are preservedth rough rep laceme n t o f p l a n t ti ssue and f i l l i ng o f t i ssue po re spaces bys i l ica and o the r m inera ls . Th is is a lso ca l led pe t r i fa c t io n . The t rees fo un din the Pa in ted Deser t an d P e t r i f i ed Fores t o f the A me r ican West a re ex-amples o f th i s p rocess.

The track ma de by th e d i nosau r as it s topped by a s tream t o d r i nk andthe t ra i l o f the c rab s k i t te r ing a long th e seashore , whe n p reserved In rock ,a re a lso fossil s because they g ive us an idea o f w ha t th e fee t o f th e an i-m a l l o ok ed l i ke . The bu r rows and feed ing t races of anim als are a lso fos-s i l s ; t racks, t ra ils , b urrow s, an d t races are re ferred t o as " t race foss i ls . "P rese rva ti on b y bu r i a l i n sed imen t is one o f th e m os t im po r ta n t p ro -cesses i n the fo rma t i on o f a foss il. M an y o rgan isms d o no t d i e i n p laceswhe re sed imen t i s be ing depos i ted and thus have n o oppo r tu n i t y fo r fos -s i l i za t ion . T he possess ion o f ha rd par ts i s a l so ve ry im po r ta n t i n the fo r -m a t i o n o f a fossi l. An ima l s and p lants l i ve today fo r wh i ch the re are nokn ow n foss il ances to rs . These u nk no wn ances to rs lack ed h ard par ts, d iedwhe re n o sed imen ts we re be ing depos i ted , o r we re no t p rese rved due t o acom b ina t i on o f these t w o fac to rs . T race foss ils m ay b e the on l y reco rdw e have o f man y o f the an ima l s tha t d i d n o t possess ha rd pa r t sO ne o f the m os t i n te res ti ng s tud ies a p a leon to log i s t unde r takes i s t h er e c o n s t ru c t io n o f a n a n i m a l o r p l a n t f r o m t h e f r a g m e n t a ry f o ss ils f o u n d .In m an y cases th is is a very d i f f i c u l t p roc edu re because the var ious p ar tso f an i nd i v i du a l an ima l o r p l a n t m ay have been w ide l y sca t tered a f te rdea th , and th e sk in , musc les , an d o ther so f t pa r ts a re m iss ~n g. t i s o f t e n


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4 F O S SI L C O L L E C T I N G 1N P E N N S Y L V A N I A


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6 FOSSIL C'OLLFCTINC; IN PI NNSVL 1'4NIA

necessary t o refer t o living animals and plants to decide how t o recon-struct a fossil. Many fossils have been found that cannot yet be totall y re-constructed because they have no living relatives t o which they can becompared. After reconstruction of a number of different fossils from thesame age and environment, scientists often attempt to place them to-gether as they once musk have lived. An example of this is the sketch ofthe Devonian sea bot tom shown on page 4.

I t is importan t t o remember in co%Ieetingossils tha t what you co llectis usually only a fragment or impression of the original an imal or plant,lacking its soft parts and frequently lacking many of its hard parts. I t s al-so impor tant t o remember that the fossil organism that you discover isonly one of perhaps millions of similar individuals that may Rave lived.

OFWHAT USE ARE FOSSILS?Why study fossils? Are they more than just curiosities t o col lec t and

place in a display cabinet? The answer is, as you might guess, yes. Fossilsare the record of li fe on the earth through billi ons of years since the firstbacteria lived and the first algae began t o f orm layered mats still recog-nizable in very ancient rocks. As such they of fer clues not on ly t o the his-tory o f the development of life, b ut also t o the character of past climateson the earth and t o changes tha t have occurred o n the earth's surfaceand in its seas. Because fossils y ield in forma tion about the environmentin which they lived, they also tell us something about the history of therock i n which they are found. Knowledge of the rock history has practicaluse in the search for minera l resources such as oi l and gas, coal, and l ime-stone.The oldest known rocks of sedimentary origin contain only very primi-tive fossil animals, such as algae. As younger and younger rocks areexamined, we fin d t hat the fossils tkey contain have gradually changedand become progressively more like present-day living organisms. De-tailed study of the fossils shows that certain older groups graduallychanged (evolved) into younger groups. These changes support thetheory o f evolution, a theory wi th wh ich scientists are muc h concerned.

The differences between fossils conta ined in younger rocks and thosecontained in older rocks provide a basis for dating and identifying rocksof similar age in wide ly di fferent areas. For example, if a pa leon tologistfinds rocks in North America and South America that contain the samefossils, he can generally say tha t tkey were formed at the same ti me andthus are o f the same age.

A pa leontolog ist working for an oi l company does the same thing withfossils, but this pa leon tologist may use on ly very small fossils called mi-crofossils. The paleontologist may work with rocks that occur only in


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Pennsylvania. i f the company has fossils from an oil- producing we lldril led near Pittsburgh and drills another well in Clearfield County, thefossils may be used to ind icate t o the drille r when the dr i l l i s approachingrocks of the same age as those in the Pittsburgh wel l . This may help in de-termining how deep one has to drill before intersecting the oil-bearingrocks.

How d o fossils help us to unravel the history of the earth?The paleon-tologist has been able to determisle the conditions under which most fos-sils li ved by stirdying modern l ife. Corals, Ccsr example, today live in th eoceans. When a coral is found in a rock, it follows that the rock materialmust have been deposited o n a sea bot tom. By col lect ing a Large numberof fossils f rom al l rocks of a given age over a large area, those areas occu-pied by land and sea of t hat former time can be outlined . For example,the area s f land and sea existing in Pennsylvania 380 mi ll ion years agohas been worked o ut in this way and is shown below.

hm d and sea areasin Perarrasylvania cdl~arlng a& of Devonian eime.

Pliant fossils, l ike animal fossils, also tel%heir o wn story. Trees grow o nthe land surface. Certain assemblages of plants and trees are characteris-ti c of swamps rather than dry Band. The coals of Pennsylvania are com-posed o f trees and plants fr om such assemblages, indicating tha t dur ingthe periods of coa l format ion extensive swamps existed in Pennsylvania(see page 46).

Fossils may also be used t o determine past climates o n the earth. Cor-als, for example, are thought to have rived only in warm waters, as they


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8 FOSSIL COLLECT ING IN PENNSYLVAN I Ado today Corals foun d in rocks in Alaska indicate that the area of Alaskawas a t one time an area of warm seas

Fossils may also be used t o i dent ify and date the rocks in wh ich theyare found These fossils are know n as index fossils An index fossil gener-ally has a distinctive and easily recognizable shape, occurs commonlyover a large area, and is restr icted t o a short period of geologic time Thebest index fossils are from animals that were swimmers or floaters, sotha t they were destributed widely in the seas and oceans Some of thebest index fossils are graptolites and certain types of cepha lopods

FINDING FOSSILSAlthough fossil-bearing (fossilifcrou\) rocks are prr3sc->ntn many are~ls

of Pennsylvania, fossils are no t alwavs easv t o col lec t They are tound on-Iy in sedimentarc. rocks, such as Binle\tone, shnle, and sandstone, andthen only in a small porti on of these types st rocks I t you are a beginningfossil collector, yo u are advised to visit locdlitles cf~~gc rlbe dn this booksn order t o become acqua inted wit h the types of rock that conta in fossilsand t o f ind o ut what fossils l ss k l i ke

In this book fossil localiti es are described fo r 5 2 sf Pennsylvania's 67counties. A ma p o f Pennsylvania showing the loc at ion of each of the sitesis on page 50. A detailed Iocatiora map also accompanies each site de-scription. Pennsylvania highway maps and topographic maps may furtheraid the coll ecto r i n find ing the localities described

in addit ion t o a description of the hcpsbil srtes, we include a l ist of thegeneric names o f fossils we have found at each slte, the t ype of rock andits geologic age, and other inf orm ati on that m ay be of snterest to the co l-lector We expect tha t careful searching at dnv loca lity wi ll uncover adds-tionas genera of fossils not given rn the fistsFor the ambitious collector, the I980 edit ion of the Ceoioyrc Map o fPel?nsylvania (Map 1 o f the Penn~y lv ~ tn ideologscal Survey) will be ofgreat aid This map shows the many rock foamatlons throughout the"state If a sedimentary rock formation ~s roun d to contain fossils at oneplace, it is l ikely to contain foss~ls liewhere After learning which rockunits conta in foss~ ls, eter to this geologrc mclp o fsnd o ther ;arec3sunder-lain by the same rock units You mac then explore these areas for add#-tisnal loca!ia~es

COURTESY IN COLLECTINGOveruse of ~3 srtsa bv students and e ~ p l o a t ~ ~ t r c ~ nt site for commercsal

purposes have resulted sn the r Bosrng to the put~ lscot tw o famous locall-tle.8, as we l l r ? ~everdl l e l s s fanjc,u\ \ l te\, In the paS t two decade^ Please,


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INTROOUCT ION 9do not do anything that wi l l cause property owners to remove l oca l i t i esdescribed herein from future collecting.

Remember that in almost a l l cases the site a t which you are collectingi s on private property. If possible, obtain permission from the owner be-fore you collect. Even roadside exposures within the highway "right-uf-way" are private property. I f someone quest ions your presenceat a road-side exposure, explain your activity and request permission to continuecollecting. Do not destroy fences or other private property and do notleave litter. Other peoplemay want to vis i t this site, and careless or heed-less actions on your part may destroy this opportunity for them.

COLLECTING AND PREPARING FOSSILSThe collector should take to the fossil locality a hammer, scrap paper,and a collecting bag.A hand lens i s usefulwhere the fossils are smal lA chisel-edge hammer, such as that used by bricklayers. i s most con-

venient for both breaking rock from the outcrop and for splitting thesample along natural layers. The rock at some local i t ies is weathered sothat it i s fragile and easily broken,whereas a t other local i t ies it may beunweathered and very d i f f i cu l t to break.Specimens collected in th e field should be wrapped in layers of paperto preserve them; i t i s then most convenient to place them in a c o l l e c t ~ n gbag. I t i s important that specimens be labeled with the loca l i ty and anyother pertinent information when they are col lected. Labeling at col lec-tion time will allow the specimens to be properIv identified at a la terdare. A sample of the lab el used by the Pennsylvania Geolog ica l Surveyis shownon the following page.

After the fossils have been collected, it i s often necessary to cleanthem by removing any dirt and rock layers that hide part of the specimen.It is advisable to wash the nonfragile specim~nswith water and a softbrush and then to work on the rock w i th var ious ch ipp ing and scrapingtools, ranging in sire from cold chisels to f ine needles, depending on thesize and fragility of the fossil. Old denta l probes, if you can obta in them,may be sharpened easily into heedle and chisel points and make vervuseful tools in cleaning fossils. Fragile specimensmay b e protected witha coating of clear plastic spray or clear nai l pol~sh.Af te r ind ividu al fossils have been cleaned and prepared, identificationlabels should be made out for each specimen, giving the local i ty, the fos-sil's name, and the nameo f the collector.

One of the best virtues of a f oss i l col lec tor i s pa t ience Many of thevery best specimens that have been col lected come from sitting in onespot at a fossil i ferous outcrop and patiently examin ing each piece ofrock for fossils.


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Eq~alpmentof thewell-p~spaaedesstl callecf~r.

IDENTIFYING AND CLASSIFYING FOSSILSA fossil-collecting expedi tion is complete onl y when the fossils f ound

have been given their proper names. A l l fossil plants and animals can beclassified in to progressively more limi ted categories unti l a generic and aspeci fic name (genus and species) is applied, The fi rst step, a simple onein most cases, is t o decide i f the fossil is an animal o r plant (Kingdom Ani-malia or Kingdom Plarotae). Then the fcassii is placed in its proper phylum[plural: phyla) and class. Classes are subdivided in to families and fami-lies i nto orders; these are mainly of interest to scientists and are no t dis-cussed here. The section of this book enti tled "'Characteristics of the Ma-jor Fossil Groups" (page 14) contains descriptions of the various phylaand classes and will help you classify your specimen i n the proper cate-gory-The final refinement of the identifi cation is to determine the genus(plural: genera) and species o f the fossil specimen you have found. A l l in-dividual specimens of the same species may not look exactly alike, butthey w i l l have many features in common. Phis you can see by observingindividuals of the species t o whi ch you belong (Homo sapiens). You canbest iden tify the genus of the fossils you ccsilect by compar ing them wi thpictures of fossils. The sketches at the back sf this book illustrate most ofthe fossils you are like ly t o encounter at t he localities described in thebook.

Fossils on these plates are genera lly no t shown at their actual size be-cause of space limitations. The amount sf reduction or enlargement i s


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shown u nde r each foss i l ske tch . The f igu re ""x0.8"means tha t the p i c tu reis e ight- tenths the s ize o f the actua l speeinaen. Keep in mind, however ,tha t a l l spec imens o f th e same genus will n o t be the same s ize, just as a l lH o m o sapiens are n o t the sam e s ize. 181ustra tions o f foss i ls n o t shown o nth es e p l a te s m a y b e f o u n d i n o n e o r m o r e o f t h e b o o k s l i s t e d in t h e " A d -d i t i ona l Reading" sec t ion nea r the end s f th i s book . Tw o o f th e mos t use -fu l re fe rences a re lndex Fossils o f N or th Amer ica, by Sh imer and Shrock ,an d th e Treatise on I nve rteb rate Pa leonto lagy , pub l i shed by the Geo log i-ca l Soc ie ty o f Am er i ca and th e U n i ve rs i t y o f Kansas.

The examp les be lo w show h ow th ree d id ferent organisms are ciassi f iedin t o va r ious ca tegor ies . The names m ay seem s t range because they a rebased upo n La t i n and Greek wo rds, bu t this has been don e so tha t thenames ma y be used and p rono unced a i l o v e r t h e wo r l d i n a n i n te r n a t io n -a l system (code) o f zoo log i ca l nom enc la tu re

Category Example 1 Example 2 Example 3KIN(;DC),%~ Plantae Animalia AnimaliaPEJY~IM Tracheophyta Brachiopoda ChordataC L A ~ ~ Cymnospermae Articlnlata MammaiiaG EN i s Pinus A trypa HomoSPEC/[ s robus reticularis sapiensl u u ~ v r o v a ~ Wh it e pine tree Sea shela Man

It is c o m m o n p r a c t i c e t o s i m p l i f y f r e q u e n tl y u s ed n am e s b y d r o p p i n go r chang ing end ings. For examp le , members o f th e ph y lu m Brach iopodaa re ca l l ed b rach iopods ; members o f the c lass M am m a l i a a re ca l l ed m am -mals . The generi c an d spec i f ic names are no t used in fo rm a l l y and a re a l -ways w r i t t e n as you see them above , fo l l ow ing ru les o f the In te rna t i ona lCode .

GEOLOGIC T IMEThe ear th has been i n ex is tence fo r ove r 4,000 m i l l i on years To be ab le

t o t a lk a b o u t p o r t i o n s o f this vas t am ou nt o f t ime , sc ien t is ts have sepa-ra ted i t i n to d iv i s ions (ca l led eons , e ras, a nd periods) , w h i ch a re charac-te r i zed by ce r ta in k inds o f foss il s . I n fac t , foss ils w ere on e o f the o r ig ina lmeans by w h i c h the bounda r ies be tw een these va r ious t im e d i v is i onswere es tab li shed . The ac cep te d t im e d iv i s ions a re shown on the geo log ict ime sca le on the fo l l ow ing page . The f i r s t co l umn shows the t imes a tw h ic h the va r ious per iods s tar ted , i n m i l l i o ns o f years b e fo re the p resen tThe second co lumn ind ica tes some o f the charac te r i s t i c an ima ls andp lan ts tha t l i ved i n these pe r iods o f the ear th 's h i s to ry The th i rd co l um nshows the many t ypes o f r ocks fo rmed i n Pennsy l van ia du r i ng ce r ta i npe r iods o f t im e . I f yo u exam ine the t ime sca le , you w i l l see tha t du r i ngmo st o f the Ju rass ic an d Cre taceous Periods n o sed iments w ere depo s i t -


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FOSSIL C OLLEC I INC ii\i F 'ENNS) LL 'A N I A

LIFE RECORD ROCK RECORD GEOLOGIC NAM ES ~9 ~3d Z

TYPICAL FOSSI LS PREDOMINANT PERIODS 5 2ROCKS

CAMBRIAN

PRECAMBR IANB A C T E R I A

Geologic tHme scale.


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INTRODllC7 ION 13

ed i n Pennsylvania. We thus assume that Pennsylvania was mainly a landregion during these periods. Therefore we have no fossil record of l i fedur ing these periods in Pennsylvania. The fou rth and fi ft h coIumns l istthe period, era, and eon names that we use for the various divisions oftime. As you can see, it is mu ch easier t o say that you found a Devonianage fossil than t o say that you found a fossil between 365 and 405 mil l ionyears old . The period names wi ll be used a great deal in later portions ofthis book.

The geologic time scale is the standard t o whi ch scientists refer in dat-ing the various portions o f the earth's history. Using this standard,paleontologists can study what occurred all over the world at any onetime The periods and eras represent, in general, times dur ing which ma-jor geologic events took place, such as the fo rmat ion of a range of msun-tains or the depos ition o f a certain suite of rocks. Many Bong and detailedbooks have been writt en o n the subject of geologic t ime and the manygeologic events tha t have taken p lace since the earth began. For those in-terested in this fascinating subject, references are given i n the section on"Additional Reading."

Fossil Collecting in Pennsylvania Part 1 of 3

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