64 CHEMUNG GROUP. 



CHAPTER XXIII. 



CHEMUNQ QROUF 3 . 



133. This Group was named from the exposure at the Chemung Upper 

 Narrows, at Chemung, New York, and defined by Vanuxem and Hall in 1842 and 

 1843. The shale and sandstone at Ithaca, having a thickness at Hector's Falls of 

 400 feet, was called the Ithaca Group, but it is only part of the Chemung. The 

 Chemung consists of a highly fossiliferous series of shales and thin-bedded sandstones 

 and impure limestones, and an infinite variety formed from admixture of these. 

 Except in a few localities there is no marked line between it and the Portage below. 

 The two are distinguished by their fossils. The shales vary in color from a deep 

 black to olive-green, with every grade of intermixture ; the sandstones are gray, olive, 

 or green, and almost the whole series weathers to a brownish olive. The Group 

 forms an east and west belt across the southern part of New York, having a thick- 

 ness in the eastern part of 2,000 feet, dipping southerly at 25 feet or more to the 

 mile, and thinning westwardly, so as not to be determined a short distance from 

 where it crosses the line of Ohio. It is unknown farther west. In its extension 

 from Eastern New York into Pennsylvania the thickness increases until it exceeds 

 3,000 feet. It occurs at New Brunswick and at Gaspe, Canada, but has not 

 been satisfactorily determined at many other places, though it probably occurs in 

 many other regions of the Appalachian system. The rocks which have been called 

 Chemung in Ohio, Indiana, Illinois, Missouri, Iowa, and Michigan belong to the 

 Waverly, except the thin, tapering belt in North-eastern Ohio, already mentioned. 



134. The alternations and interlaminations of shales and sandstones show 

 deposition under similar circumstances to those under which the Portage was de- 

 posited. The source of the materials was to the east or south-east of New York, 

 as evidenced by the thinning of the deposits and diminution of sandy strata toward 

 the west. The land-plants occur in Eastern New York, and disappear westerly, 

 proving the land existed in that direction. The marine and land plants are abun- 

 dant in the sandstones, while marine shells increase with the decline of the sand- 

 stones and augmentation of the shales westerly, though fucoids continue in abundance 

 wherever the Group exists. The plants foreshadow the approaching Carboniferous 

 System by the presence of Archceopteris, Cydopteris, Sigittaria, Lepidodendron, and 

 Trigonocarpon. The fauna has more of a Carboniferous aspect than any which pre- 

 ceded it, and there is a diminution of the types which characterized the earlier 

 Devonian. The species having the greater distribution and most characteristic 

 are Lepidodendron cJiemungense, Archceopteris laxa, A.fterophyllites parvulus, Orthis im- 

 preftna, Orthix tioga, Streptorhynchu* chemiingense, S. pectinaceum, Strophodonta eayuta, 

 S. mucronata, Chonetex muricatus, Productella hirsida, Spirifera disjuncta, S. memcos- 

 talis, Atrypa dumoza, A. hystrix, Aviculopectzn duplicatus, A. nigwtriatus, Leptodesma 

 longinpinum, L. xpinigerum, Leiopteria chemungensw, Pterinopecten dispandw, P. 

 crenicostatus, P. suborbieularis, Pterinea consimilis, Grenipecten crenulatus, Mytilarca 

 chemungemia, and Phacops nupera. 



135. Springs, evolving carbureted hydrogen-gas, or gas accompanied with 

 petroleum, are common throughout nearly all that part of New York and Peunsyl- 



