BOOK XVIII. 



GEOLOGY. 



WITH regard to Geology, as a Palaetiological Science, I do not 

 know that any new light of an important kind has been thrown 

 upon the general doctrines of the science. Surveys and examinations 

 of special phenomena and special districts have been carried on with 

 activity and intelligence ; and the animals of which the remains people 

 the strata, have been reconstructed by the skill and knowledge of zoo- 

 logists : of such reconstructions we have, for instance, a fine assem- 

 blage in the publications of the Palaeontological Society. But the 

 great questions of the manner of the creation and succession of animal 

 and vegetable species upon the earth remain, I think, at the point at 

 which they were when I published the last edition of the History. 



I may notice the views propounded by some chemists of certain bear- 

 ings of Mineralogy upon Geology. As we have, in mineral masses, 

 organic remains of former organized beings, so have we crystalline 

 remains of former crystals ; namely, what are commonly called pseu- 

 domorphoses the shape of one crystal in the substance of another. 

 M. G. Bischoff 1 considers the study of pseudomorphs as important in 

 o-eolooy, and as frequently the only means of tracing processes which 

 have taken place and are still going on in the mineral kingdom. 



I may notice also Professor Breithaupt's researches on the order of 

 succession of different minerals, by observing the mode in which they 

 occur and the order in which different crystals have been deposited, 

 promise to be of great use in following out the geological changes 

 which the crust of the globe has undergone. (Die Paragenesis der 

 Mineralien. Freiberg. 1849.) 



In conjunction with these may be taken M. de Senarmont's experi- 

 ments on the formation of minerals in veins; and besides Bischoff 's 



1 Chemical and Physical Geology. 



