OR UPPER NEW-YORK ROCKS. 
199 
Summary of facts respecting the upper rocks of the new-york, Silurian, and 
DEVONIAN SYSTEMS. 
1. The series of rocks above the Tully limestone consists of alternating masses of sand¬ 
stone, slate and shale. The greatest mass of slate is the Genesee slate; and the 
greatest mass of sandstone, in continuous beds, is the Portage group. 
2. The rocks, from the Genesee slate to the conglomerates of the Coal, form one series ; 
and though this series is divided into groups, the subordinate divisions are made for 
convenience rather than utility or necessity: they serve, however, one or two pur¬ 
poses, namely, those parts of the series which have intercalated members, or other 
differences, are more fully brought to view, the economical portions may be clearly 
defined, and the comparison of two distant points is made more striking. It will be 
said that the groups are important, and an appeal may be made to the fossils for 
sustaining the position. The better division of the series seems to he into upper 
and lower, or upper, middle and lower. The division of the rocks above the 
Taconic, and below the Coal, into two great systems, the Silurian and Devonian, 
simplifies the study of the geology, and encumbers the mind of the student less than 
that which makes many subordinate parts. The deepest part of the Devonian sea 
appears to have been in the region of the Catskill series; and if we may form an 
opinion of the continuous depth of such a sea, from the extension and thickness of 
a formation, it would seem that the depth increased rapidly upon the eastern shore, 
but shallowed more slowly to the southwest. This view seems to be sustained by 
the fact that the prolongation of the Silurian and Devonian systems eastward is 
quite limited, some of the beds of the Lower Silurian extending only five or six 
miles east of the city of Hudson ; while in order to place ourselves in the midst of 
a deep silurian and devonian sea, we have only to travel ten miles southwesterly 
from this city. The whole mass composing both systems disappears at once, as it 
were, on the eastern side, thinning out suddenly ; and the Taconic slates, plunging 
down at a steep angle, form a basis upon which the whole is supported. 
3. There is less difference between the lower part of the Devonian and upper Silurian in 
New-York, than there is between the Champlain and the Ontario divisions. 
4. The economical products are fine and valuable flags, quarries of which may be opened 
through a wide horizontal as well as vertical range. The rock contains neither 
ores, limestones, nor brine springs. 
5. Some of the springs, which issue from the Genesee slate, are liydrosulphuretted in an 
eminent degree; while the springs of the rocks above the slate, are pure as those 
of a primary district. 
6. The country underlaid by these rocks is hilly, and the slopes afford an excellent soil 
for grazing. Wheat, though not the natural crop, is still raised on the bottoms of 
the narrow valleys. 
