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Notes on American Geology. 243. 
when coming in contact with the surface of a glacier; however — 
slightly inclined from the horizon, many of the boulders might 
of course traverse the extreme’ limit of the slope, and without 
losing their angular form ; but the limestone fragments being 
imbedded in.the bottom of the glacier would be only affected in 
position by contraction and expansion of the ice, and the more 
extensive movements caused by its breaking up in melting, 
which would have ample power to wear down the angles d 
these fragmentary rocks. 
Occasionally T have seen the upper rioters rot \inebaaeaa and 
sandstones-broken up, a distance of several feet from the surface, 
but the fragments remain in situ. Now who can imagine such 
an appeararice to result from a current of water? Floods, how- 
ever violent, do not tear up the solid rocks in this manner, and if 
they did, how could these fragments have withstood their force 
and remained unmoved from their original position? Indeed, I 
think it impossible to account for this breaking up of the rocks 
- to a distanee of many feet below ‘the surface, except by the 
agency of intense cold, freezing the water which filled the fis- 
sures, and thus forcing the rocks into tabular fragments, and dis- 
turbing their bosties by the lateral and upward pressure. 
Remarks on_ the Transition or Silurian System. 
_- "The rocks constituting the Transition or Silurian system, have 
been much neglected by geologists, and yet in consequence of 
their embracing the’ remains of the first created beings, and af- 
fording us an insight into the earliest physical condition of the _ 
globe, they have peculiar attractions both for the reason and ima- 
gination : indeed, the facts are colored to the eye of i inexperience 
with all the exaggeration of romance. If we only content our- 
selves patiently to investigate the organic remains, the more they 
are carefully studied do they gain in interest, and prove to be as 
readily classified as any of the later formations, notwithstanding 
their inclined position and disturbed stratification. Without such 
knowledge, every step will be embarrassed, and- years of labor 
may be unprofitably devoted to the subject. An instance of 
error on the large scale may be observed in the second annual. 
report of the geological exploration of Pennsylvania; where the 
hocosian of the Hudson river is confounded with a rock, some-_ 
similar, it is true, in mineral character, which abounds in 
