October 1, 1894.] 



KNOWLEDGE. 



•2-21 



liglit. In the absence of any knowledge regarding the 

 radiation of gases under the enormous pressures and 

 temperatures which must obtain in the deeper layers of 

 the photosphere, it would be hazardous to assert that the 

 continuous spectrum of these regions is in any way 

 analogous to the continuous spectra of the comparatively 

 dense vapours that I have subjected to experiment. 



THE ANCIENT MAMMALS OF BRITAIN. 



III. — The Lower Tertiary Period. 

 By R. Lydekker, B.A.Cantab., F.R.S. 



BETWEEN the coralline crag and the Hempsted 

 beds of the Isle of Wight, which belong to the 

 middle portion of the Oligocene period, and are 

 the next Tertiary deposits met with in Britain, 

 is a long gap, owing to the complete absence of 

 all representatives of the Miocene and upper Oligocene 

 strata of the Continent. In consequence of this imperfec- 

 tion of the record, instead of finding a gradual transition 

 from the mammals of the crag period as we pass down- 

 wards through the Miocene beds till we reach the Oligocene, 

 we notice that the mammalian fauna of the lower Ter- 

 tiaries of Britain is utterly unlike that of the upper beds, 

 and shows not the faintest trace of connection with it. 

 In place of deer, rhinoceroses, horses, and pigs we have, 

 even in the highest beds of the lower Tertiaries, ungulate 

 mammals of strange and unknown types, all of which 

 belong to genera long since extinct, and differing widely in 

 the structure of their low-crowned cheek-teeth from all 

 modern mammals, although some appear to have approxi- 

 mated in external form to the tapirs and others to the 

 pigs. Elephants and mastodons were entirely unknown, 

 and the place of monkeys was filled by primitive lemur- 

 like creatures. All the indications aftbrded by the flora 

 and the moUuscan life of the Oligocene and Eocene beds 

 point to the conclusion that during those epochs Britain 

 enjoyed a tropical or sub-tropical climate ; and, in some 

 respects, its faima may be compared to that of Madagascar 

 at the present day, although, of course, the genera of the 

 mammals, and in many cases even the families were 

 different. Indeed, of the land mammals inhabiting Oligo- 

 cene and Eocene England, only two groups can be referred 

 to genera that still exist, one of these being now relegated 

 to the New World. 



Lest the reader should begin to think that the whole of 

 the strata whose fauna we have to consider in this part of 

 our subject belong to nearly the same geological period, we 

 hasten to point out the various groups into which they are 

 divided, preparatory to the consideration of their fauna. 

 The highest of the Oligocene beds in Britain are those 

 forming the steep clay clifi's on the western side of the Isle 

 of Wight, in the neighbourhood of Yarmouth, and termed 

 the Hempsted beds, from a village of that name which is 

 situated upon them. These belong to the middle portion 

 of the Oligocene period, and have a fauna similar to that 

 of certain beds at Konzon, near Puy-en-Velay, in the 

 Haute Loire. Next in descending order are the Bembridge 

 beds of the Hampshire basin, whose fauna corresponds 

 with that of the gypsum beds on which Paris stands, and 

 which are consequently assigned to the lower part of the 

 Oligocene ; the beds of Hordwell, in Hampshire, and 

 Headon, in the Isle of Wight, likewise belonging to the 

 same great division. The clays of Barton, in Hampshire, 

 which, like those next mentioned, unfortunately yield 

 scarcely any mammalian remains, bring us to the upper 

 portion of the Eocene period ; while the older clays of 

 Bracklesham, in Sussex, are assigned to the middle 



division of the same epoch. Better known than these is 

 the London clay, forming the upper portion of the lower 

 Eocene, and yielding several types of mammals ; beneath 

 which are the unfossiliferous Woolwich and Reading beds, 

 resting on the chalk. Before proceeding to the considera- 

 tion of the fauna of these various beds, it may be observed 

 that mammalian remains are for the most part rare and 

 fragmentary, and that for a full knowledge of the extent 

 of the fauna of the period, and the structure of its com- 

 ponent items, we have to depend largely upon the 

 discoveries made on the Continent or in the United States, 

 both of which are more favoured than Britain in regard to 

 the preservation of early Tertiary mammals. In our survey 

 of the fauna of all these beds, it will be more convenient 

 to treat of the animals according to their zoological 

 position, indicating the difl'erent horizons in which they 

 severally occur. 



At the present d;iy, as explained in a former article, 

 lemurs are chiefly characteristic of Madagascar, although 

 likewise occurring in Africa, and also represented in south- 

 eastern Asia, but in the Oligocene period they were 

 abundant in Europe. One of these early lemurs was 

 described from the Hordwell beds as far back as the year 

 1844 under the name of Micmrhuriiii, but it is only 

 recently that its true aflinities have been recognized. Not 

 much larger than a squirrel, this creature approximated in 

 the structure of its skull to the African lemurs known as 

 galagos, but differed from all the existing members of the 

 group in that the lower tusk was formed by the canine 

 tooth and not by the first tooth of the premolar series. 

 Still more difi'erent from any living lemur was the 

 Oligocene Ailapis, first described from France, and regarded 

 as an ungulate, but subsequently recognized from the 

 Hordwell beds. It difi'ers from all modern lemurs in 

 the presence of four pairs of premolar tfeeth in each 

 jaw, and one of the species attained a comparatively 

 large size, its skull measuring upwards of four inches in 

 length. 



• In Madagascar lemurs are now accompanied by many 

 kinds of insectivores, and it is, therefore, not surprising 

 to find a member of that order in the Hordwell beds. This 

 animal (Xen-oi/i/mtuini), instead of being allied to the 

 Malagasy insectivores, appears, however, to have been 

 related to the gymnura of Borneo, which may be described 

 as a long-tailed hedgehog without spines, and therefore 

 somewhat rat-like in general appearance. Civets likewise 

 form an important element in the modern Malagasy fauna, 

 and the Hordwell lemurs were accompanied by a member 

 of that group assigned to the existing Afi-ican and 

 Oriental genus Viverra, which includes the true civets. 

 With the exception of the opossums, this civet is the only 

 terrestrial mammal from the earlier British Tertiaries which 

 can be referred to a still living genus. The other early British 

 carnivores belong to an extinct group known as the 

 creodonts, which disappeared with the close of the 

 Oligocene period, and differed from modern carnivores in 

 that all their molar teeth were furnished with sharp 

 cutting blades, instead of a single pair of cheek-teeth in 

 each jaw being specially modified for cutting with a 

 scissor-like action. In their dentition these primitive 

 carnivores approximate, indeed, both to the insectivores 

 and the marsupials, and they are undoubtedly far more 

 generalized types than the existing members of the order 

 to which they belong. While some were not larger than 

 a fox, others fully equalled the dimensions of the largest 

 bears. In Britain they are represented by one genus 

 (thixnodon) from the Hordwell beds, by a second (Pteioilun) 

 from the Bembridge limestone, and a third (Anii/lntlirrii'ni) 

 from the London clay. The last is, however, only known 



