160 PROGRESS OF SCIENCE. 



1687 1750. Moro was the first to point out that ROCKS 

 must have been DEPOSITED as soft mud, some by the sea, for 

 they contain marine fossils, others by rivers, for they contain 

 fresh-water plants and animals, and that they were subse- 

 quently upraised by earthquakes from time to time. After 

 him comes 



1726 97. Hutton, who may be called the FIRST GREAT 

 GEOLOGIST in point of time and importance. He travelled 

 and made many scientific explorations in order to collect 

 facts, and from these he was able to ascribe the changes on 

 the earth's surface to volcanic action and subterranean heat, 

 thereby originating the PLUTONIAN (or Vulcanian) THEORY, 

 the exclusiveness of which, entertained by Plutonists gene- 

 rally, though not by Hutton himself, is now discarded. 

 Hutton also indicated the processes of denudation, erosion, 

 formation of valleys, river channels, and the action of running 

 water, which levels mountains, carries their materials to the 

 ocean, and thus helps to prepare the sea-floor to become new 

 continents, when in the course of time it is uplifted by under- 

 ground forces all of which modes of action modern geologists 

 have proved to be well founded in fact. He also explained 

 the theory of rain, and threw great light on the study of 

 meteorology. The most important lesson he taught, how- 

 ever, and the one for which he will always be remembered, is 

 that the history of the past must be studied by the changes 

 going on at present, and that THE LAWS which regulated the 

 economy of the globe in past ages were the same as those 

 NOW IN OPERATION (1788); so that he was the precursor of 

 Lyell in teaching the PERMANENCY OF LA.W. These theories, 

 owing to the influence of the Wernerian school, and the want 

 of elegance and lucidity of style of Hutton's Theory of the 

 Earth, were held in little repute for some time. 



1743 1822. Hauy enunciated the theory of CRYSTAL- 

 LISATION that it takes place in accordance with geo- 

 metrical laws and classified minerals in accordance with 

 their crystallisation. 



1748 1819. Playfair (John) studied the geological system 

 of THE ALPS, and threw additional light upon geological 

 laws. It is, however, by his popularising the views of 



