The Glacial Theory of Prof. Agassiz. 347 



sion, which has been adopted in whole or in part by Professor Buck- 

 iand, Mr. Lyell, and other eminent geologists, has been deduced from a 

 careful study of the phenomena attending glaciers, some of which are 

 of so marked and peculiar a kind, as to afford satifactory evidence of 

 their ancient existence in situations where none are now seen. The 

 Swiss philosopher advanced in his opinions step by step. He first sat- 

 isfied himself that in the Alpine valleys where glaciers still exist, they 

 once rose to a higher level, and extended farther down into the low 

 country than they now do. Next he discovered indications of their 

 former existence on Mount Jura and over the whole Swiss valley ; and 

 connecting these with similar indications found in the Vosges, the Scan- 

 dinavian Mountains, and elsewhere, and with the well known fact of 

 sheets of ice covering the northern shores of Siberia and entombing 

 the remains of extinct species of animals, he came to the conclusion, 

 that at a period, geologically speaking, very recent, all the old world 

 north of the 35th or 36th parallel, had been enveloped in a crust of ice. 

 Whence the cold came which produced this efiiect, and why it after- 

 wards disappeared, are questions he did not feel himself bound to an- 

 swer, but which might, perhaps, be answered hypothetically. In real- 

 ity, if we suppose the Northern Atlantic from the 39th parallel filled 

 up and converted into dry land, it is extremely probable that Britain 

 would have the ice-bound climate of Labrador, with which it corres- 

 ponds in latitude ; and the conversion of the said land into sea would 

 bring back the order of the seasons which we now enjoy. Even 

 though M. Agassiz's opinions should not be fully established, they still 

 aflTord us a new geological agent of great power and widely applicable, 

 which may help us to an explanation of some phenomena very difficult 

 to account for with our existing means of information. 



Form, Magnitude and Composition of Glaciers. — The subjoined 

 figure is not a section, but a view of a glacier as it would present itself 

 to an eye raised considerably above it. 



a b, (fig. 1,) The gla- 

 cier : a represents one of, 

 the forms of its surface, 

 in which it is bristled with 

 cones of snow or ice, call- 

 ed aiguilles or needles : h 

 is the other and more usual 



form of the sui'face, con- ''^'^■''^ -tsma^ 



sisting of narrow ridges or corrugations, like waves fixed by frost. 



c d, Lateral moraines, consisting of long lines of boulders and gravel, 

 which having been detached by frost, rain, lightning, or avalanches, 

 from the rocks flanking the valley, settle on the two sides of the glacier. 



