Icebergs upon Drift. 451 



"The objections that the surfaces of the rocks must have 

 been often protected from the action of the moving icebergs 

 by intervening mud and sand, and that the lower portions of 

 icebergs could not correspond with the uneven surfaces of the 

 rocks, and leave the traces of their progress ahke on the 

 mountain-sides and in the valleys, cannot be met by any facts 

 above presented, as to the form and nature of movement of 

 icebergs. We may, therefore, conclude that they have not 

 been the sole instruments in furrowing and grooving the 

 rocks beneath the drift. 



2. The immense magnitude of the icebergs in our present 

 seas, and the evidence of their present mechanical power, 

 when moved by strong currents, warrant the conclusion 

 that they must have exerted a powerful influence in pushing 

 and crowding along the sand and gravel which formed the 

 bottoms of the ancient seas, and in thus forming accumula- 

 tions somewhat analogous to the moraines of the glaciers. 



3. The length of time during which large icebergs may 

 remain aground, even when swept by rapid currents, which 

 currents might surround them with sand and mud, or sweep 

 away the loose materials, leaving hills or banks upon spots 

 protected by the stranded icebergs, favor the idea that this 

 agency had an influence in giving the present form to our 

 drift. 



4. The formation of glaciers or fixed icebergs, upon the 

 present coasts, under such circumstances that fragments of 

 rock, and detritus from the land upon which they form, be- 

 come attached to them, the constant advance and separation 

 of the glaciers from the land, and their floating into the sea 

 as icebergs, with their loads of earth and rocks, lead to the 

 conclusion that icebergs, breaking off' from the shores of 

 ancient seas, were important agents in the transportation of 

 rocks and earth from their parent beds. The existence of 

 immense fragments of rock, in situations where they could 

 not have been carried by water alone, as on the sides of hills, 

 with valleys intervening between them and their parent beds, 



