122 THE OLDEST MAMMALS. 



shells imbedded in the fragments of rock in which the 

 mammalian jaws are contained. Here we may mention 

 that the Stonesfield slate is the equivalent of the lower 

 portion of the great, or Bath, oolite a deposit which is 

 separated from the underlying lias by the beds known as 



the inferior 

 oolite. Conse- 

 quently, the 

 mammal -yield- 

 ing beds are 

 separated from 

 the rocks of the 

 FIG. 38. One half of the lower Jaw of a Tertiary period 

 Stonesfield Mammal. Twice natural size. The . -/ V ,1 ' 



restoration of the front teeth is conjectural. n v D J t . ne 



immense series 



of Cretaceous deposits (chalk, gault, greensarids, and 

 Wealden), but likewise by a large thickness of those 

 belonging to the Jurassic system, such as the Purbeck 

 and Portland oolites, the Kimeridge clay, the coral-rag, 

 and the Oxford clay. 



Needless to say, no sooner was the existence of mammals 

 in the Stonesfield slate announced than it was received 

 with a howl of incredulity. First of all it was attempted 

 to show that the specimens themselves did not come from 

 Stonesfield ; and no sooner was this objection knocked on 

 the head than doubts were raised as to the Jurassic age of 

 the Stonesfield slate itself. These, however, were equally 

 soon disposed of, and the only thing then remaining was 

 to dispute the mammalian nature of the fossils. This task 

 was undertaken by the French naturalist, De Blainville, 

 who attempted to show that the mammalian character of 

 the specimens was not proved by the double roots of their 

 molar teeth. In the course of the argument, great stress 

 was laid on the circumstance that two-rooted molars were 

 found in a gigantic animal from the Eocene of the United 

 States, then known as Basilosaurus, and regarded as a 

 reptile. De Blainville was, however, here treading on very 

 dangerous ground, for it subsequently turned out that 

 Basilosaurus itself was really a mammal, which is now 

 generally placed among the whales, under the name of 



