42 PROGRESS OF PALEONTOLOGY n 



out a long space of time. Within the last few 

 years this has been done fully in the case of the 

 horse, less completely in the case of the other 

 principal types of the ungulata and of the car- 

 nivora; and all these investigations tend to one 

 general result, namely, that, in any given series, 

 the successive members of that series present a 

 gradually increasing specialisation of structure. 

 That is to say, if any such mammal at present 

 existing has specially modified and reduced limbs 

 or dentition and complicated brain, its predecessors 

 in time show less and less modification and reduc- 

 tion in limbs and teeth arid a less highly developed 

 brain. The labours of Gaudry, Marsh, and Cope 

 furnish abundant illustrations of this law from the 

 marvellous fossil wealth of Pikermi and the vast 

 uninterrupted series of tertiary rocks in the terri- 

 tories of North America. 



I will now sum up the results of this sketch of 

 the rise and progress of palaeontology. The whole 

 fabric of palaeontology is based upon two proposi- 

 tions : the first is, that fossils are the remains of 

 animals and plants ; and the second is, that the 

 stratified rocks in which they are found are sedi- 

 mentary deposits ; and each of these propositions 

 is founded upon the same axiom, that like effects 

 imply like causes. If there is any cause competent 

 to produce a fossil stem, or shell, or bone, except 

 a living being, then palaeontology has no founda- 



