MUSEUM OF COMPARATIVE ZOOLOGY. 53 



expect to find it so throughout the temperate and cold zones of the 

 southern hemisphere, with the sole exception of the present glaciers of 

 Tierra del Fuego and Patagonia, which may have transported houlders 

 in every direction. Even in Europe, geologists have not yet sufficiently 

 discriminated between local glaciers and the phenomena connected with 

 their different degrees of successive retreat on one hand, and the facts 

 indicating the action of an expansive and continuous sheet of ice moving 

 over the whole continent from north to south. Unquestionably, the 

 abrasion of the summits of the mountains of Great Britain, especially 

 noticeable upon Schiehallion, is owing to the action of the great Euro- 

 pean ice-sheet during the maximum extension of the glacial phenomena 

 in Europe, and has nothing to do with the local glaciers of the British 

 Isles. 



Among the facts already known from the southern hemisphere are 

 the so-called rivers of stone of the Falkland Islands, which attracted 

 the attention of Darwin during his cruise with Captain Fitzroy, and 

 which have remained an enigma to this day. I believe it will not be 

 difficult to explain their origin in the light of the glacial theory, and I 

 fancy now they may turn out to be nothing but ground moraines, similar 

 to the " Horsebacks " of Maine. 



You may ask what the question of drift has to do with deep-sea 

 dredging? The connection is closer than may at first appear. If drift 

 is not of glacial origin, but the product of marine currents, its formation 

 at once becomes a matter for the Coast Survey to investigate, and, I 

 believe, it will be found in the end, that, so far from being accumulated 

 by the sea, the drift of the lowlands of Patagonia has been worn away 

 to its present extent by the continued encroachment of the ocean in the 

 same manner as the northern shores of South America and of Brazil 

 have been 



Hoping some, at least, of my anticipations may prove true, 

 I remain, ever truly yours, 



LOUIS AGASSIZ. 

 Prof. Benjamin Peirce, 

 Superintendent Coast Survey, Washington, D. C. 



