164 HUTTONIAN THEORY 



as for the cause of science, his devoted friend and 

 disciple, Playfair, at once set himself to draw up an 

 exposition of Hutton's views. After five years of 

 labour on this task there appeared the classic Illus- 

 trations of the Huttonian Theory, a work which 

 for luminous treatment and graceful diction stands 

 still without a rival in English geological literature. 

 Though professing merely to set forth his friend's 

 doctrines, Playfair's treatise was in many respects an 

 original contribution to science of the highest value. 

 It placed for the first time in the clearest light the 

 whole philosophy of Hutton regarding the history of 

 the earth, and enforced it with a wealth of reasoning 

 and copiousness of illustration which obtained for it 

 a wide appreciation. From long converse with Hutton, 

 and from profound reflection himself, Playfair gained 

 such a comprehension of the whole subject that, dis- 

 carding the non-essential parts of his master's teaching, 

 he was able to give so lucid and accurate an exposition 

 of the general scheme of Nature's operations on the 

 surface of the globe, that with only slight corrections 

 and expansions his treatise may serve as a text-book 

 to-day. In some respects, indeed, his volume was 

 long in advance of its time. Only, for example, 

 within the lifetime of the present generation has the 

 truth of his teaching in regard to the origin of 

 valleys been generally admitted. 



Various causes contributed to retard the progress of 

 the Huttonian doctrines. Especially potent was the 

 influence of the teaching of Werner, who, though he 

 perceived that a definite order of sequence could be 

 recognised among the materials of the earth's crust, 



