560 HISTORICAL PALAEONTOLOGY. 



Pecten Islandicus. 

 Astarte borealis. 

 Leda oblonga. 

 Saxicava rugosa. 

 Tellina proximo,. 

 Tel Una solidula. 

 Leda truncata. 

 Astarte compressa. 



Trophon clathratum. 

 Natica clausa. 

 Scalaria Grcenlandica. 

 Bucdnum undatum. 

 Purpura lapillus. 

 Fusus Islandicus. 

 Littorina littorea. 



III. POST-GLACIAL DEPOSITS. Under this head are in- 

 cluded various fluviatile deposits, such as brick-earths, low- 

 level and high-level gravels, and all those accumulations which 

 are generally understood by the terms " cave-deposits," " ossi- 

 ferous breccias," and the like. The fossils of these deposits 

 consist chiefly of the bones of Mammals, both living and 

 extinct, in many instances mixed with the bones, or, more 

 commonly, the implements of man in his earliest and rudest 

 condition. Most of the Pre-glacial Mammals which have 

 been previously enumerated, survived the Glacial period, and 

 appear in Post-glacial deposits; but along with these are 

 other forms some extinct, some still in existence which are 

 not known to have lived in times prior to the Glacial epoch. 

 The following list is given by Mr Boyd. Dawkins of the 

 Mammals which inhabited Britain during the Post-glacial 

 epoch : 



LIST OF POST-GLACIAL MAMMALS. 



Palaeolithic Man. 



The Glutton (Gulo luscus). 



The Cave Bear ( Ursus spelaus) ? 



The Grizzly Bear (Ursus ferox) ? 



The Cave Lion (Felis leo=Felis spelaa). 



The Cave Hyaena (Hycena spel&a). 



The Panther (Felis pardus). 



The Musk-sheep (Ovibos moschatus). 



The Tichorhine Rhinoceros (R. tichorhinus). 



The Mammoth (Elephas primigenius). 



The Lemming (My odes Icmmtis). 



The Cave Pika (Lagomys). 



The Pouched Marmot (Spermophilus). 



Spermophilus erythrogenoides. 



GEOGRAPHICAL SUCCESSION OF ORGANIC FORMS. 



A few words may be said here on a law which may be called 

 the " law of the geographical succession of organic forms," 

 and which is illustrated more completely by the Mammalia 

 than by any other extinct animals. An examination, namely, 

 of the facts of the geological distribution of Mammals, leads to 

 the striking generalisation that " the present distribution of 

 organic forms dates back to a period anterior to the origin of 



