194 HISTORY OF GEOLOGY AND PALEONTOLOGY- 



to Lyell, local rise of temperature in the earth's crust, so that 

 larger and smaller reservoirs of melted rock-material may 

 accumulate. If the water and gases impregnating the rocks 

 are converted into vapour, volcanic eruptions and earthquakes 

 ensue. The slow elevations of the ground are also referred by 

 Lyell, in the later editions of the Principles ; to subterranean 

 rise of temperature and to the consequent expansion of the 

 solid rocks, whereas decrease of temperature or the removal of 

 gaseous material gives origin to subterranean cavities, inthrows, 

 and subsidences. 



Lyell was during the greater part of his life an opponent 

 of Lamarckism. In the early editions of the Principles, he 

 recognised the occurrence of constant change in the organic 

 world, but refused to associate the modification of living forms 

 with any definite history of evolution during the successive 

 geological ages. He began with the fundamental question 

 whether changes in the animal and plant world were still in 

 progress, or if organic creation had already arrived at its 

 highest development. After discussing Lamarck's views on 

 the produption and modification of organs, Lyell enumer- 

 ated a number of data regarding the limits of variability 

 of wild and domestic species and the results of cross- 

 breeding, and expressed his conviction that each species 

 had been created with the characteristics still presented by 

 it. He allowed that species can to a certain extent accom- 

 modate themselves to their environment, but asserted that 

 the possible changes were slight, and rapidly accomplished, 

 having no influence upon the essential characteristics of 

 the species. He held that unlimited variability was further 

 prevented by the natural aversion of species in the wild 

 state to cross breeding, and by the small fertility of hybrids. 

 Lyell afterwards revoked these opinions, a change in his 

 views having been effected by the writings of A. R. Wallace 

 and Charles Darwin. 



The two famous papers of these authors on the variability of 

 species appeared simultaneously in the year 1858 in the 

 publications of the Linnaean Society. Darwin's epoch-making 

 work on the Origin of Species by Natural Selection was 

 published in the following year, and another work of that year 

 was W. Hooker's Flora of Australia. 



Lyell, together with the great zoologist Huxley and the 

 philosopher Herbert Spencer, at once enthusiastically accepted 



