66 PROGRESS OF SCIENCE 



than the Association. We may date the modern 

 development of stratigraphical study in Britain from 

 the work of William Smith (1769-1839). The rocks, 

 older than the Coal Measures, which were left un- 

 touched by him, were investigated by two of our own 

 most eminent figures of the earlier years : Sedgwick 

 in North Wales and Murchison in South Wales. 

 Later, the classification in detail of strata according 

 to their points progressed rapidly through the efforts 

 of many observers, while in 1840 Agassiz, visiting 

 Britain, adduced a new conception of the origin of 

 much of the surface covering of our islands 

 through glacial agency, though his opinions did not 

 for some time obtain general adoption. Meanwhile, 

 the knowledge of the physiographical side of geology 

 remained in a rudimentary condition : the general 

 tendency was to assign the origin of existing land- 

 forms to some convulsive operation of nature, and 

 such movements or processes as submergence and 

 elevation, erosion and denudation, were very imper- 

 fectly understood, if at all. Controversy arose be- 

 tween ' catastrophist ' and ' unif ormitarian ' schools 

 of thought. The first sought evidence that the 

 operations of nature were in earlier periods of the 

 history of the earth's formation more powerful and 

 spasmodic than at the present time, and that in 

 these processes early races of plants and animals 

 were wholly destroyed, to be replaced by new ones. 

 The unif ormitarians, basing their ideas upon extended 

 applications of Hutton's views, admitted no evidence 

 of alteration in geological causes. Lyell, leader of 

 this school, in the maturity of his presidential address 

 to the Association in 1864, adverted to ' two points 

 on which a gradual change of opinion has been taking 



