Paheozoic IBxtory of l\rins<ylvama. — ClaypoJe. 157 
we here catch a glimpse of one of them, or at least of the place 
where it entered the sea. 
In making this supposition to explain the occurrence of the 
Hamilton sandstone, it is not at all necessar}- to assume that this 
ancient river came into existence at that epoch and then passed 
out of being. Far from it. The river ma}' have existed ages be- 
fore that da}' and maj' have continued to flow long after the Ham- 
ilton era passed awa}'. All that is necessar}- is to suppose an ac- 
cession to its carrying power. And this is not difficult. The 
palaeozoic geology of the eastern states indicates beyond all doubt 
constant and great oscillation of the land and the seabed. Inter- 
mittent depression to immense extent caused the accumulation of 
the massive sediment of that era. Such accumulation likewise in- 
directly proves elevation of the land, for had not this taken place 
the whole area must have been eroded and removed. It is less 
easy to detect elevation of the laud than depression of the sea 
bottom, because the former leaves no direct evidence of its occui-- 
rence. But if the Hamilton sandstone is in truth the monument 
of some old and extinct river, it records a time when through ele- 
vation of the coast the eroding and carrying power of that river 
were largely increased so as to form the Hamilton lower sand- 
stone. Next it indicates a time when probably bj- the work of 
the river, but possibly by ensuing subsidence, the current was 
again slowed down and the sand dropped near shore, its quautitv 
being also diminished. Thirdly, it reveals another sharpening of 
the stream \)\ a second elevation whereby- it was enabled to erode 
from the laud and scatter over the ocean bed the Hamilton upper 
sandstone thicker than the lower. Lastly, the action of the river 
destroyed its own velocity by eroding its channel or a second sub- 
sidence ensued with the same eti'ect. 
All these episodes are to be read with great probability in tin- 
Hamilton sandstone, and if our argument is well founded we gain 
a peep at one of the changes of which the palaeozoic era was made 
up. 
Possibl}' though this is little more than a supposition ; the ab- 
sence of lime from the Devonian formation through tiiis part of 
Pennsylvania may be an indication in the same direction. The 
beds show a preponderance of the earthy and mechanical over the 
chemical deposits such as is usual near the mouth of a river where 
the wash from the land predominates over all other materials. 
