THE OLDEST MAMMALS. 121 



CHAPTEE XII. 



THE OLDEST MAMMALS. 



UP to the year 1818 it was a generally received axiom of 

 geology that mammals were totally unknown before the 

 Tertiary period ; and that period was consequently 

 designated the age of mammals a name, by the way, 

 which is still perfectly appropriate, if taken to imply that 

 these animals then, and then only, became the dominant 

 inhabitants of the world. In that year, however, the 

 illustrious Cuvier, during a visit to the museum at Oxford, 

 was shown two minute jaws, carrying a number of cusped 

 teeth, which had been obtained in the neighbouring 

 quarries of Stonesfield, from the rock known as the 

 Stonesfield slate, belonging to the lower part of the great 

 Jurassic, or Oolitic, system. After careful examination, 

 the French anatomist pronounced confidently that these 

 two tiny little jaws, neither of which exceeded an inch in 

 length, were those of mammals, and he further suggested 

 that they would prove to belong to a species of opossum. 

 Although this opinion was given in the year 1818, it does 

 not appear that it was published till the year 1825, when 

 the second edition of the fifth volume of the immortal 

 ' Ossements Fosiles " saw the light. In publishing this 

 epoch-making notice of the occurrence of mammals in the 

 Secondary period, Cuvier, with the usual caution of 

 naturalists, was careful to add the proviso that everything 

 depended on whether the specimens he saw had really 

 been obtained from the Stonesfield slate. Unfortunately, 

 there does not appear to be any record stating by whom, 

 or at what date, these original specimens now forming 

 some of the most valued treasures of the Oxford Museum 

 were obtained from the Stonesfield slate ; but that they 

 did come from that formation is perfectly certain. Indeed, 

 other specimens have been subsequently obtained from the 

 same beds, showing certain characteristic Stonesfield 



