CHEMUNG (she-mfing') GROUP. A series of sandstones and shales of marine origin. consti tuting the uppermost member of the Devonian system in southern and western New York and eastern Pennsylvania, and deriving its name from the Cbemung Narrows, near Elmira, N. Y., where the formation \vas first described. The Chemung group formed the top of the 'New York system' of the early New York State Geologi cal Survey. It succeeds the Portage group, which it conformably overlie,. and which it re sembles in the shallow-water character of most of its deposits. The rock- are mostly shales, though sandstones are frequent, and a pudding stone bed, known a- the Panama Conglomerate, occurs in the western part of New York. at a horizon about 250 feet below the top of the group. In the vicinity of its original locality. near Elmira, the Chemung group has a thickness of about 1500 feet: it thins westward toward the Pennsyl•ania-( )11 io line. when' it disappear:. To ward the east it changes its character, the marine deposits giving way to the estuarine and brack ish-water deposits of its littoral facies, the Cat-kill group ((IN.). Southward, through eastern Pennsylvania. the thickness of the marine deposits and along the northern Ap palachian :Mountain- the group from 3500 to 41000 feel thick. Its southward continuation be low Pennsylvania has not been well determined.
The Chemung rock-, as a rule, abound in fossil contents. Brachiopods are most abundant, in places forming whole layers of rock, where the shells were washed together by currents and strewn over the shallow hott(mts. Land plants, prophetic of the forms seen in the later coal measu•es, arc common in the more easterly por tions of the formation, especially in the estuarine beds of the Catskill series, where a large fern, Arelneopteris (q.v.), is often found. At several
localities in western New York have been found large numbers of Di•tyospongidm (q.v.), allies of, and probably when alive just as beautiful as, the modern glass-sponge (Ellp/cculla). The characteristic fossils are: 1;raehiopods—Spiri fer disjunctus, -I.trypa hystrix. and A. spinosa, Rhynchonella contracta, Produ•tella lachrymosa: Pelecypods—Pterinea ehemungensis, Grammysia subarcuatus, Prorhynehus nasutum, Schizodus chemungensis. Some phyllmarid crustacen have been found, and in a few localities 'fish-bed:' have yielded good examples of lloloptychins, Bothriolepis, etc. The economic products of the Chemung consist of building-stone, and oil and gas in the western counties of New York.
Binuounienv. Williams, "On the Fossil Fau nas of the Upper Devonian. etc.." in Bulletin \ o. of the United States Geological Surrey ( ington, 1884) ; "(n the Fossil Faunas of the Upper Devonian; The Genesee Section," in Bulle tin No. 4 of the United States ticologieal Sor rell 1887) : Prosser. "The Classifi cation and Distribution of the Hamilton and Chenmng Series of Central and Eastern New York," Part 1., in Forty-ninth Annual Report York State Museum, Vol. H. (Albany, 18981 ; Part IL, op. cit. 51st, Vol. II. (Albany, 1599) Stevenson, "The Chemung and Catskill on the Em-tern Side of the Appalachian Basin." in Proceedings American Association. Adrance merit of Science, Vol. XL. (Salem, 1891). See, also, DEVONIAN SYSTEM : CAI SKILL GROUP: CLAY : BRICK ; OIL; GAS; PETROLEUM.