Notes on American Geology. 243 



when coming in contact with the surface of a glacier, however 

 shghtly inchned from the horizon, many of the boulders might 

 of course traverse the extreme hmit 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 of 

 these fragmentary rocks. 



Occasionally I have seen the upper portions of limestones and 

 sandstones broken up, a distance of several feet from the surface, 

 but the fragments remain in situ. Now who can imagine such 

 an appearance 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 distance of many feet below the surface, except by the 

 agency of intense cold, freezing the water which filled the fisr 

 sures, and thus forcing the rocks into tabular fragments, and dis- 

 turbing their position 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 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 

 graywacke of the Hudson river is confounded with a rock, some- 

 what similar, it is true, in mineral character, which abounds in 



