DESCRIPTIONS OF THE FORMATIONS. 35 



had crumbled away. On the Genesee River the group is not less than 1000 feet 

 thick. The Portage yields less lime to the soil than the Hamilton, but for 

 pasturage it is superior to it. H. 224. The great dairy-country of Cortland, and 

 other counties in Central New York, is on the Portage formation. The water of 

 the Portage group is remarkably pure and soft. The Portage rocks have not been 

 recognized in the eastern part of New York. In Ohio the Portage forms the upper 

 part of the Huron shale, and the lower part of the Erie shale, of Dr. Newberry. 



In Middle Pennsylvania, according to Lesley, the Portage flags are 1,450 feet 

 thick, and the Chemung shales over them, 1,860 feet thick. It is very hard to draw 

 a line of demarcation between them, but, as a whole, the Chemung strata are 

 more silicious and the Portage more argillaceous. The Portage sandstones are 

 flaggy, and, at times, very shaly, and their alternations with shale frequent, the 

 individual beds being thin, and the shales predominant. The Chemung sandstones 

 are more massive, ferruginous and micaceous, with fewer alternations of shale. 

 Brachiopods and other shells are abundant in the upper Chemung shales, while the 

 Portage rocks are almost destitute of animal forms except crinoids and f ucoids. 

 Fucoidal impressions are also very abundant in the upper Chemung, and to the 

 decomposition of this abundant marine vegetation, Lesquereux and others ascribe 

 the origin of the petroleum, at its various local horizons, from the Portage up to 

 the Mahoning sandstone in the Coal Measures. 



11 b. Chemung. These rocks can everywhere be described as a series of 

 thin-bedded sandstones and flagstones, with intervening shales, and mixtures in 

 various proportions of these, and very rarely beds of impure limestone, resulting 

 from the aggregation of organic remains. The whole series weathers to a brownish 

 olive, and even the deeper green of the shales assumes that hue. The shales vary 

 in color from a deep black to olive and green, with every grade and mixture of 

 these. The sandstones are often brownish-gray or olive, and sometimes light gray. 

 More generally, however, there is a tinge of green or olive pervading these strata. 

 Towards the upper part of the group, in some localities, there is a tendency to 

 conglomerate, and in a few places the mass becomes a well defined pudding-stone, 

 with sometimes 150 to 200 feet of Chemung shales and sandstones above it. 

 Towards the upper part of the group the shales are reddish, coarse and fissile, 

 with much mica in small glimmering scales. Hall 251 . From their red color 

 these have sometimes been mistaken for the Catskill formation. 



In a few localities in Pennsylvania it contains a very excellent variety of iron 

 ore. As a general thing, however, this formation, and all others above it, up to 

 near the coal conglomerate, are singularly deficient in iron ore. There is little of 

 geological interest throughout the whole extent of the Chemung group. The N. 

 Y. L. E. & W., or Erie Railway, runs for 300 miles west of Susquehanna on this 

 formation, and on nearly the same portion of it. In the northwestern portion of 

 Pennsylvania the celebrated OIL EEGION is in the Chemung, the oil being found 

 stored-up in certain coarse porous sandstones, but these are merely the repository 

 of the oil originating in lower strata. It is a very extensive formation in Southern 

 New York, all the southern tier of counties, west of Great Bend, being covered 

 by it, and it forms an excellent grazing and agricultural country, not quite equal 

 to the Portage, but much superior to the Catskill. In Northern Pennsylvania this 

 formation, as in Southern New York, consists of a vast succession of thin layers 

 of shale, of every hue, from a deep olive and dark green to a light slaty gray, 

 alternating with thin beds of brownish gray sandstones. 



