648 HISTORY OF SCIENCE. 



these doctrines. He held that the extinction of former species of 

 vegetables and animals was due to great cataclysms, and that new 

 species were afterwards created afresh, or, at least, that the distribution 

 of land animals was repeatedly changed. The opposite doctrine is 

 identified with the name of the late Sir CHARLES LYELL (1797 1875), 

 the first edition of whose "Principles of Geology" appeared in 1830. 

 Lyell's doctrine asserted that geological changes in past time have 

 been continuous and unitorm with those in progress at this day. 

 Cataclysmic revolutions brought about by paroxysmal forces are re- 

 garded by Lyell as gratuitous assumptions. Much disputation was 

 carried on for years between the Catastrophists and the Uniformitarians, 

 but Lyell's view? have finally been everywhere accepted. That ail 

 the changes which have ever occurred on the face of the earth have 

 been produced by the causes now in action that is, by forces distri- 

 buted in similar proportion and acting with like intensity to those we 

 now observe is, it may be supposed, not the position contended for ; 

 but that these causes will account for the visible facts of geology if 

 we admit a sufficiently extended time for their operation. 



Among the more remarkable geological discoveries of the present 

 century may be named that of evidence of epochs of intense cold 

 having formerly prevailed over the now temperate regions of the 

 earth. It was observations on existing glaciers that enabled AGASSIZ 

 (1807 1874) to recognize over parts of Northern Europe and America 

 traces of glaciers which once filled the valleys or extended in vast 

 sheets over the land. Agassiz was appointed Professor of Natural 

 History at Neuchatel in 1832, and he soon afterwards published a 

 great work on fossil fishes, in which he did for the extinct species of 

 this class of vertebrates what Cuvier (page 402) had done for the fossil 

 mammalia. In 1864 Agassiz was induced to accept a professorial 

 chair in the United States, where he spent the remainder of his days 

 in scientific work, greatly honoured by the citizens of his adopted 

 country. It was of him that Longfellow wrote : 



And he wandered away and away 



With Nature, the dear old nurse, 

 Who sang to him night and day 



The rhymes of the universe. 



And whenever the way seemed long, 



Or his heart began to fail, 

 She would sing a more wonderful song, 



Or tell a more marvellous tale. 



The mechanism of glacier motion yet remains a puzzle to physicists 

 and naturalists, notwithstanding the investigations of De Saussure, 

 Forbes, Charpentier, Agassiz, Tyndall, Viollet-le-Duc, and others. 

 Further research into the action of glaciers and icebergs, and the ex- 

 ploration of the vast regions of eternal frost which surround the Poles, 

 would doubtless disclose many facts of the utmost importance to the 



