CONTENTS xi 



Natural Selection : the keynote of the Darwinian Theory. The 

 fittest to survive are not necessarily those which are ideally 

 most perfect. 



Changes in environment. Geological evidence of changes of climate 

 in England and in Greenland. 



Comparison between Natural and Artificial Selection. Natural 

 Selection acts for the good of the Species. Artificial Selection 

 is directed solely towards the benefit or the pleasure of Man. 



LECTURE III. (Pp. 53-77.) 

 THE ARGUMENT FROM PALEONTOLOGY. 



The Structure of the Earth's Crust. A series of superposed layers or 

 . strata, composed of various materials, originally deposited for 

 the most part under water, and subsequently raised above the 

 surface. 



Fossils are the actual remains, as bones, teeth, shells, etc., or the 

 indications, as, e.g., footprints, of the animals that formerly in- 

 habited the earth. Amongst them, were our collections com- 

 plete, would be the entire series of the ancestors of all living 

 animals. The actual age of Fossils cannot be determined, but 

 their relative ages are known from the position of the strata in 

 which they are found. 



The Imperfection of the Geological Record. Only certain parts of 

 certain animals can be preserved as fossils : special conditions 

 are necessary for their preservation, and for their subsequent 

 exposure at places accessible to man. It is irrational to expect 

 fossils to yield continuous series of forms, save under exceptional 

 circumstances. " A Chapter of Accidents." 



The Geological Evidences of Evolution. Life on the earth has been 

 continuous. Cuvier's Cataclysms have no place in nature. In 

 passing from the older to the more recent strata, there is a 

 general advance in organisation, and a gradual approach 

 towards the existing condition. Fossils are " generalized 

 forms " rather than directly intermediate links. The geological 

 history of the Horse, of Birds and Reptiles, and of Paludina. 



The Extinction of Species. Persistent types. Comparison of the 

 Geological Record with the History of Man. 



