148 A CENTURY OF SCIENCE 



in which other causes were easily eliminated. Sculpture 

 by glaciers passed beyond the theoretical stage when the 

 simple forms of the Sierras and New Zealand Alps were 

 described. The origin of loess was first discerned in a 

 region where glacial phenomena did not obscure the 

 vision. The complexity of the Glacial period asserted by 

 geologists of the Middle West was denied by eastern 

 students. The work of waves on the English coast 

 impressed British geologists to such an extent that plains 

 of denudation and inland valleys were ascribed to 

 ocean work. 



In the establishment of principles, the friendly inter- 

 change of ideas has yielded large returns. Many of the 

 fundamental conceptions of earth sculpture have come 

 from groups of men so situated as to facilitate criticism. 

 It is impossible, even if desirable, to award individual 

 credit to Venetz, Charpentier, and Agassiz in the formu- 

 lation of the glacial theory ; and the close association of 

 Agassiz and Dana in New England and of Chamberlin 

 and Irving in Wisconsin was undoubtedly helpful in 

 establishing the theory of continental glaciation. Prom 

 the intimate companionship in field and laboratory of 

 Hutton, Playfair and Hope, arose the profound influence 

 of the Edinburgh school, and the sympathetic cooperation 

 of Powell, Gilbert, and Button has given to the world its 

 classics in the genetic study of land forms. 



The influence of ideas has been closely associated with 

 clarity, conciseness, and attractiveness of presentation. 

 Hutton is known through Playfair, Agassiz 's contribu- 

 tions to glacial geology are known to every student, while 

 Venetz, Charpentier, and Hugi are only names. Cuvier's 

 discourses on dynamical geology were reprinted and 

 translated into English and German, but Lamarck's 

 "Hydrogeologie" is known only to book collectors. The 

 verbose works of Guettard, although carrying the same 

 message as Playf air's "Illustrations" and Desmarest's 

 "Memoirs," are practically unknown, as is also Horace 

 H. Hayden's treatise (1821) on the drift of eastern 

 North America. It has been well said that the world- 

 wide influence of American physiographic teaching is due 

 in no small part to the masterly presentations of Gilbert 

 and Davis. 



