sae i 
STEVENSON. 29 
Chemung and Catskill, 
White to be the same with the first Venango sand (Lachkawacen 
conglomerate). Wherever the fishes are associated with any other 
form of animal life, that form is marine, so that the ordinary 
presumption should be that the fishes themselves are marine. 
A study of the fauna and its distribution shows us that, as far 
as any evidence exists, the conditions were marine from the be- 
ginning of the Chemung period to the close of the Catskill; that 
in the early Chemung, or possibly in the Hamilton, the conditions 
within northeast Pennsylvania and the adjacent portion of New 
York became unfavorable to the free development of animal life; 
and that as time went on, these conditions were gradually ex- 
tended southward and westward, so that, toward the close of the 
Chemung, they prevailed in Columbia county, fifty miles south- 
east from the Delaware river and in Bradford county, about the 
same distance west from the outcrop line. Before the close of the 
Catskill they had reached southward beyond James river in Vir- 
ginia, but had not extended much further west in Pennsylvania 
and New York. But, though prevented from existing in the 
muddy shallows, the animals existed further west in the basin, 
beyond reach of the river silts, so that just as soon as an oppor- 
tunity was afforded by a lull in the untoward conditions, the 
active fishes found their way eastward again, to be followed, if 
the interval were long enough, by the more sluggish mollusks as 
in New York and in Roanoke and Russell counties of Virginia. 
a few words concerning it, and T have 
One matter still remains 
done. 
What are the relations of this great Chemung-Catskill group to 
the Lower Carboniferous? 
The Pocono or Vespertine or Lower Carboniferous sandstone, 
the lower division of the Lower Carboniferous, is practically non- 
fossiliferous throughout central and southern Pennsylvania, the 
only animal remains thus far discovered being those of mollusks, 
seen by Prof. White* in Bedford county, Pennsylvania, and those 
of fishes seen by Prof. Stevensont in Fayette county; but these 
have not been studied and their relations are stillunknown. The 
upper beds of the Pocono become calcareous in southwest Vir- 
ginia where the mollusks are unquestionably Lower Carboniferous. 
The plant remains, obtained in Pennsylvania, are for the most 
*Geology of Huntingdon County, p. 81. 
tGeology of Ligonier Valley. p. 57. 
