656 FOSSIL MAMMALIA 



dimensions of the common hedgehog or the squirrel. On this subject 

 Dr. Falconer observes, that in the Miocene freshwater deposit of Seissan, 

 in the Department of Gers, near the Pyrenees (so well explored by M. 

 Lartet), there is a layer in the marginal part of the basin in which the 

 bones of diminutive mammalia, such as shrews and others, are mixed 

 with remains of frogs in profusion ; while in a more central part of the 

 same basin, entire carcasses of the Mastodon aud other huge animals oc- 

 cur. In like manner the thin layer No. 93 in Purbeck may represent 

 the shallow margin of a river, lake, or lagoon, in the deeper parts of 

 which fossil animals of greater size may be preserved. 



On a review of all the fossils collected by Messrs. Brodie and Beckles, 

 including the original Sjialacotherium, together with a lower jaw be- 

 longing to the Rev. P. B. Brodie, and communicated to me by Prof. 

 Owen, it appears that we now possess (March 14th) the evidence of 

 about fourteen species of mammalia from the Middle Purbeck, to say 

 nothing of numerous remains of the highest osteological interest, respect- 

 ing which no opinion can be hazarded until they have been studied more 

 in detail. They beloDg to eight or nine genera, some insectivorous or 

 predaceous, others having affinities as yet doubtful, and one of a purely 

 herbivorous type, allied to the Kangaroo-rat of Australia. Some of the 

 predaceous species were marsupial, some of them, in the opinion of Dr. 

 Falconer, probably placental. 



As all of them 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 tribu- 

 taries. They afford the first positive proof as yet obtained of the co- 

 existence 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, except 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 con- 

 spicuous a part, numerically considered, the mammalian species of the 

 Middle Purbeck now play when compared with those of other forma- 

 tions 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.* 



° In drawing up this table I have been assisted by Professor Owen, in refer- 

 ence to the British, and by MM. Lartet and Hebert in reference to the fossil 

 mammalia of the French Eocene strata. There are, besides, several undescribed 

 species in the collection of the two last-mentioned paleontologists, or in mu- 

 seums known to them ; and in regard to one or two of the Eocene continental 

 localities out of the Paris basin, the age of the deposits is too little known to 

 allow us to include their fossils in the Table. 



