12ij THE OLDEST MAMMALS. 



shells imbedded in the fragments of rook in whicli the 

 mammalian jaws are contained. Here we may mention 

 that the Stonesfield slate is the equivalent ot the lower 

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

 separated from the underlying lias by the bieds known as 



the inferior 

 oolite. Conse- 

 I'tuently, the 

 maramal-yield- 

 iuLC beds are 

 sejiarated from 

 the rocks of the 



Fig. .38. — One half of the lower Jaw of a XertiaiT period 

 Stonesfield Mammal. Twice natural size. The ^^^:^^ only by the 

 restoration of the front teeth is coniectural. . ' -f ■' . 



immense series 



of Cretaceous deposits (chalk, gault, greensands, 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 incredvility. 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 w^as 

 to disiiute 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 Basilosawrns, and regarded as a 

 rejitile. 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 



