ADDENDA. 



619 



I will now endeavour to show how far these very curious facts, which 

 we owe to M. Agassiz's observation, can be explained by the theory of 

 floating ice : and the theory, I may add, if applicable to this case, solves 

 that which presents far greater difficulties, than any other of the kind 

 in Europe. I should first state that I make two assumjitions, and if these 

 be rejected, the theory is not applicable to the case of the erratic blocks 

 of the Alps : — first, that an arm of the sea extended between the Jura and 

 the Alps, during that period in which, as I have before shown, it is probable, 

 that the proportional area of water in Europe was greater, and certain, 

 that the productions of the land and water had a more tropical character, 

 at the same time that the snow-line descended lower. The age of the 

 Molasse, which occupies this area, between the Jura and Alps, has not 

 been accurately determined ; but it is supposed to be miocene, and is 

 said to contain leaves of the Chamserops, a genus of palms, at present 

 found further from the equator than any other kind. It is not, however, 

 evident that the Molasse was deposited by the sea during the latest 

 period, when it occupied a confined limit between the Alps and Jura ; 

 but even if this should be found to be the case, it would be rash in any 

 one positively to conclude that glaciers could not have descended to the 

 shores of a sea, on which the Chamasrops flourished, after that we know 

 they descend in the southern hemisphere so near the limits of several 

 tropical forms. 



My second assumption is, that the elevation of this much of Switzer- 

 land, whenever it took place, was slow and gradual : this is supported by 

 the strongest analogies of South America, Scandinavia, and other parts of 

 the world ; whilst on the other hand, the assumption that it had been sudden, 

 would be unsupported by a single ascertained fact in nature. Now, as 

 the numerous masses of ice, which fall from the glaciers at the head of the 

 sounds on the South American coast, are slowly drifted outwards (owing 

 to the fresh water flowing in from the foot of the glaciers), and in the more 

 open channels are left to be acted on by the winds and currents ; so must 

 it have been with the icebergs from the glaciers of the Alps, situated in 

 the same latitude, and under similar conditions. These icebergs would in 

 most cases be driven on some part of the surrounding shore ; but from 

 floating deep they would ground a little way from the beach, and then 

 being packed together, and driven to and fro, as the winds changed, and as 

 the tides rose and fell, would they not, like a glacier on the land, though 

 in a lesser degree, "bruise and grind down every thing and polish the sohd 

 surface, on which they reposed ?" In the rapids of the North American 

 rivers, over which large bodies of ice are driven, carrying with them peb- 

 bles and fragments of rocks, I am informed by Dr. Richardson, that the 

 primitive rocks are scooped and hollowed, and have their surfaces polished 

 and glossy. Dr. Richardson, however, is not prepared to say, whether this 



