658 OOLITIC MAMMALIA. 



him in the same set of rocks through Sussex and the Isle of Wight. 

 They appear to belong to 3 or 4 species of reptiles, but no one of them 

 to any warm-blooded quadruped. They ought, therefore, to serve as a 

 warning to us, when we fail in like manner to detect mammalian foot- 

 prints in older rocks (such as the New Red Sandstone), to refrain from 

 inferring that quadrupeds, other than reptilian, did not exist or pre-exist. 



But the most instructive lesson read to us by the Purbeck strata con- 

 sists in this : — They are all, with the exception of a few intercalated 

 brackish and marine layers, of fresh water-origin ; they are 160 feet in 

 thickness, have been well searched by skilful collectors, and" by the late 

 Edward Forbes in particular, who studied them for months consecu- 

 tively. They have been numbered, and the contents of each stratum 

 recorded separately, by the officers of the Government Survey of Great 

 Britain. They have been divided into three distinct groups by Forbes, 

 each characterized by the same genera of pulmoniferous mollusca and 

 cyprides, but these genera being represented in each group by different 

 species ; they have yielded insects of many orders, and the fruits of 

 several plants ; and lastly, they contain " dirt beds," or old terrestrial 

 surfaces and soils at different levels, in some of which erect trunks and 

 stumps of cycads and conifers, with their roots still attached to them, 

 are preserved. Yet when the geologist inquires if any land animals of 

 a higher grade than reptiles lived during any one of these three periods, 

 the rocks are all silent, save one thin layer a few inches in thickness, 

 and this single page of the earth's history suddenly reveals to us in a 

 few weeks the memorials of so many species of fossil mammalia, that 

 they already outnumber those of many a subdivision of the tertiary 

 series, and far surpass those of all the other secondary rocks put to- 

 gether ! 



It is remarked by Professor Owen that many of the Purbeck Insec- 

 tivora belong to the same natural family as those of Stonesfield. Some 

 at least of them were Marsupials, and Dr. Falconer has pointed out 

 that the Plagiaulax of Purbeck, an herbivorous marsupial, was so much 

 allied to the Microlestes of the Trias as to lead us to infer that that 

 more ancient mammifer was likewise a pouched quadruped, having some 

 affinity to the living Kangaroo-rat. 



In Australia and the neighboring islands about 100 species of mar- 

 supials exist, together with a certain number of placentals (bats and 

 rodents), while the fossil species of that continent show that kangaroos, 

 wombats, Tasmanian wolves (or Thylacines), dasyures, and other mar- 

 supials of species now extinct, preceded the present creation. Although 

 the localities of Stuttgardt, Stonesfield, and Purbeck, do not relate to 

 an area larger than the middle island of New Zealand, yet there may 

 have prevailed, during the Oolitic period, throughout a much wider 

 space in European latitudes, certain geographical and climatal condi- 

 tions and a peculiar vegetation, favorable to a fauna more analogous to 

 that of the present Antipodes than to that of modern Europe. During 

 the Upper Triassic, the Liassic, and Oolitic epochs, one assemblage of 



