DYNAMICAL GEOLOGY. 195 



and upheld the newly-founded doctrine of descent. And the 

 tenth edition of the Principles, published in 1866, contains an 

 excellent account of the leading principles of Darwin's work 

 and its bearing upon scientific thought. The chapter on the 

 geographical distribution of plants and animals, upon which 

 Lyell had spent considerable care in earlier editions, had to be 

 completely re-written in the light of Darwin's theory. As it 

 now stands, this chapter presents a wealth of fine observations 

 and geological conclusions, and is an admirable model of the 

 scientific treatment' of a subject. The extinction of species is 

 explained through changes both in the organic and inorganic 

 world, the appearance of new species is attributed to the 

 modification of progenitors. 



In the eleventh edition, Lyell summarised in a special 

 chapter the chief features of his work, On the Age of the Human 

 Race, which had been published in 1863. In Lyell's opinion, 

 all human races and sub-races had sprung from a uniform 

 prototype which had originated in one area of the globe. 

 All the early human remains gave evidence that the state of 

 culture of the first ancestors of mankind had been extremely 

 low ; and he saw no reason for assuming that man had taken 

 origin through any other agency than the working of those 

 universal laws which had determined the origin of species in 

 the plant and animal kingdoms generally. 



In the fourth volume of the Principles, afterwards adapted 

 as the Elements of Geology, Lyell followed the precedent of 

 Deshayes and Bronn in his sub-division of the Tertiary 

 deposits. He calculated the percentage of living molluscan 

 species present in the successive groups of the Tertiary strata, 

 and upon the percentages fixed a definite basis of sub-division 

 into Eocene, Miocene, and Pliocene formations. Lyell drew 

 his account of pre-Tertiary formations for the most part from 

 the text-books of Conybeare and De la Beche. He applied 

 the term of primary formations to the plutonic rocks and the 

 crystalline schists. Lyell opposed the idea that any funda- 

 mental distinction existed between plutonic and volcanic rocks, 

 and assumed that granitic and other coarse-grained crystal- 

 line rocks might still be in course of formation at great depths 

 below the surface, and under the enormous pressure of super- 

 incumbent rocks. He showed that granite had been intruded 

 at various geological epochs, and was by no means invariably 

 the oldest rock, as the Wernerian school had taught. Lyell 



