230 EEPORT OF THE AMERICAN COMMITTEE. 
the New York section. They are followed above by the Onon- 
daga and Corniferous limestones, averaging less than a hundred 
feet in thickness, but reaching three hundred feet in thickness or 
more, in some parts of New York and in Michigan. 
In this eastern continental area there was evidently some re- 
lationship between the sandy deposits beginning in the Oriskany, 
and the calcareous deposits typically represented in the Onondaga 
and Corniferous limestones; for we find in the northwestern part 
of the area the sandstones thinning out to almost nothing, while 
the limestones reach their greatest thickness, and in the eastern 
and more southern part of the area the sandstones reach their 
greatest thickness, while the limestone dwindles and in some parts 
has not been distinguished at all. The limestone is rich in corals, 
and in some layers has abundant Brachiopods ; the latter are 
types of wide geographical distribution, and, in the more common 
forms, such as Strophomena rhomhoidaUs and Atrypa reticularis, 
are species of long geological range. Some of the corals, too, 
have a long range in the western continental section, appearing 
in the upper part of the Nevada limestone, according to Mr. 
Walcott. 
In New York the next lithological terrane of the Devonian is 
a series of shales, often beginning and terminating in black and 
sometimes partly calcareous shales; but in the central part of the 
section, gray, soft argillaceous shales, temporarily calcareous in 
places, and holding a rich and abundant fauna, constitute the 
Hamilton series. The Hamilton also shows tendency to be more 
calcareous westward and more arenaceous in the eastern outcrops, 
and the sandstones and arenaceous shales are thicker and pre- 
dominant in the Pennsylvania, Maryland and Virginia sections, 
while the argillaceous and calcareous shales are more conspicuous 
in New York, Ohio, Canada West and Michigan. A thousand 
feet may be taken as an average for the thickness, including the 
two terminal black shales, though some of the Appalachian sec- 
tions double this thickness. In our accepted classification the 
upper Genesee black shale is grouped with the Hamilton, but, as 
I have shown elsewhere, there are good reasons for drawing the 
distincti\-e line, separating middle and upper Devonian, below 
rather than above the'Genesee shale. 
Above the Hamilton series a period of deposition of arenaceous 
shales and sandstones prevailed all over this eastern area, called 
