386 MAMMALIA OF MIDDLE PURBECK. [Ch. XX. 



ber of bones in juxtaposition. In several portions of the matrix there 

 were detached bones, often much decomposed, and fragments of others 

 apparently mammalian ; but, if all of them were restored, they would 

 scarcely suffice to complete the five skeletons to which the five upper 

 maxillaries above alluded to belonged. As the average number of 

 pieces in each mammalian skeleton is about 250, there must be many 

 thousands of missing bones ; and when we endeavour to account for 

 their absence, we are almost tempted to indulge in speculations like 

 those once suggested to me by Dr. Buckland, when he tried to solve 

 the enigma in reference to Stonesfield : — " The corpses," he said, " of 

 drowned animals, when they float in a river, distended by gases during 

 putrefaction, have often their lower jaw hanging loose, and sometimes 

 it has dropped off. The rest of the body may then be drifted else- 

 where, and sometimes may be swallowed entire by a predaceous rep- 

 tile or fish, such as an ichthyosaur or a shark." 



We may also suppose that when fish or other aquatic animals attack 

 a decaying carcase, whether it be floating or has sunk to the bot- 

 tom, they will first devour those parts which are covered with flesh. 

 A lower jaw, consisting of little else than bones and teeth, will be 

 neglected, and becoming detached, may be drifted away by a current 

 of moderate velocity, and buried apart from the other bones in sand 

 or mud. 



As all the above-mentioned Purbeck mammalia, belonging to eight 

 or nine genera and to about fourteen species of insectivorous, preda- 

 ceous and herbivorous marsupials, have been obtained from an area less 

 than 500 square yards in extent, and from a single stratum not more 

 than a few inches thick, we may safely conclude that the whole lived 

 together in the same region, and in all likelihood they constituted a 

 mere fraction of the mammalia which inhabited the lands drained by 

 one river and its tributaries. They afford the first positive proof as 

 yet obtained of the coexistence of a varied fauna of the highest class 

 of vertebrata with that ample development of reptile life which marks 

 all the periods from the Trias to the Lower Cretaceous inclusive, and 

 with a gymnospermous flora, or that state of the vegetable kingdom 

 when cycads and conifers predominated over all kinds of plants, ex- 

 cept the ferns, so far at least as our present imperfect knowledge of 

 fossil botany entitles us to speak. 



The annexed table will enable the reader to see at a glance how 

 conspicuous a part, numerically considered, the mammalian species 

 of the Middle Purbeck now play when compared with those of other 

 formations more ancient than the Paris gypsum, and at the same time 

 it will help him to appreciate the enormous hiatus in the history of 

 fossil mammalia, which at present occurs between the Purbeck and 

 Eocene periods. 



