Page:A Treatise on Geology, volume 1.djvu/112

 96 mammalia had no existence, and only came into being during the tertiary period. But this conclusion, founded upon the mere want of such remains, was easily seen to be insecure, and at length proved to be erroneous by the decision of Cuvier, that certain small jaw bones, with teeth, found in the oolitic system at Stonesfield, near Oxford, belonged to viviparous quadrupeds, and approximated to the genus.

Five specimens of these remarkable jaw bones are known, two of which are in the hands of Dr. Buckland, one belongs to Mr. Broderip, one to Mr. Prevost, and the fifth was selected by the author of this volume from an ancient collection of fossils, the property of the Rev. C. Sykes, of Rooss, in Yorkshire, by whom it was presented to the museum of the Yorkshire Philosophical Society. These specimens are of inestimable value, for were they unknown, the whole of the positive testimony that the earth, during the secondary period of geology, nourished land mammalia would vanish, and the course of inferences as to the succession of organic life on the globe be greatly modified.

Further research has shown that among the few specimens which Stonesfield has yielded in the course of the last hundred years are two clearly distinct genera, one of them containing two species.

The designations under which they have passed are various. Compared in vain to an ichthyoid type by De Blainville, to amphibious mammals by Agassiz, one section of the fossils was brought back by Valenciennes, under the name of Thylacotherium, to the marsupial division of mammalia, to which the penetrating glance of Cuvier had united it. Professor Owen adopts for them the title of Amphitherium, assigned by De Blainville, but associates them with the insectivore. The two species are named after Broderip and Prevost.

The lower jaw contained 16 teeth on each side,—the