Devonian Era in the Ohio Basin. — Claypole. 103 
ward, being nearly or quite extinct in the Catskill. The barren 
condition of the strata begins at a lower level, that is, at an 
earlier date in the northeast than in the southwest, indicating 
that conditions unfavorable to life set in sooner in the former 
than in the latter region, to which they gradually extended. 
Thus the lower Catskill beds, which are reported nearly des- 
titute of fossils in New York, carry Chemung species mingled 
with their own, in middle Pennsylvania.* These facts indi- 
cate a rapid increase of erosion in the northeast owing either to 
a more rapid elevation or as is more probable to the greater 
night attained by the land in consequence of a steady and con- 
tinuous gain of elevation upon erosion. 
In brief, then, the hypsometry and geography of the De- 
vonian show a subsiding gulf receiving the wash of an ele- 
vated land to the northeast through the great estuary of New 
York, and thus forming the varied and assorted deposits of the 
Upper beds of the Devonian era. 
The Catskill Sandstone. — The uppermost member of the 
Devonian system, as developed in the eastern part of Appa- 
lachia, is, on the principle of division here adopted, the Cats- 
kill sandstone. The geology of this remarkable stratum has 
provoked much discussion. A brief but. excellent summary of 
it has been made by professor J. J. Stevenson. t He there ably 
argues for some of the views here adopted and attempts with 
no small measure of success to correlate the upper Devonian 
strata of Pennsylvania and New York. His general section is, 
as follows : 
Catskill- — Shales and Sandstones : 
Honesdale and equivalents. 
Montrose and equivalents. 
Chemung — Shales and Sandstones. 
Lackawaxen Conglomerate. 
Shales and Sandstones. 
Allegrippus Conglomerate. 
Shales and Sandstones. 
Nothing in professor Stevenson's paper conflicts with the 
view here advanced of rapid elevation in the northeast during 
the later portion of the Devonian era, accompanied with equal 
rapid and increasing erosion, in consequence of which the de- 
* White. Second Geo!. Surv. of Penna.. G 7; Clavpolk, same series, F2 
f Chairman's address, sect. B, A. A A. S., Indianapolis, 1891. 
