152 Geological Society. 



the animals : — the northern, into which the southern forms never 

 penetrated, the latitude of Yorkshire being the boundary of the 

 advance of the southern animals ; the southern, into which the 

 northern species never passed, a line passing through the Alps and 

 Pyrenees being the limit of the range of the northern animals ; 

 and an intermediate area, in which, the two are found mingled 

 together. 



Two out of the three zones are proved by the physical evidence of 

 the Pleistocene strata. 



We see by the discoveries of Dr. Bryce, Mr. Jameson, and others, 

 that the Pleistocene mammalia must have invaded Europe during 

 the first Glacial period before . the submergence ; for the Pteindeer 

 and the Mammoth have been found in Scotland under the deposits 

 of the Boulder-clay. Dr. Falconer and others have also discovered 

 the latter animal in the preg^cial Porest-bed. The Glacial period 

 can therefore no longer be looked on as a hard and fast barrier sepa- 

 rating one fauna from another. If man be treated as a Pleistocene 

 animal, there is reason to believe' that he formed one of the North 

 Asiatic group, which was certainly in possession of Northern and 

 Central Europe in Preglacial times. 



The Pleistocene mammalia may again be divided into three 

 groups — those which came from Northern and Central Asia, those 

 fro a Africa, and those which were living in the same area in the 

 Pliocene age. Had not the animals which lived in Europe, during 

 the Pliocene age, been insulated from those which invaded Europe 

 from Ana, by some impassable barrier, the latter would occur in 

 our Pliocene strata as well as the former. Such a barrier is offered 

 by the northern extension of the Caspian up the valley of the Obi 

 to the Arctic Sea. The animals of Northern and Central Asia could 

 not pass westwards urtil the barrier was removed by the elevation 

 of the sea-bottom between the Caspian and the Urals. 



The same argument holds good as to the African mammalia, 

 which could not have passed into Sicily, Spain, or Britain without a 

 northward extension of the African mainland. 



The relation of the Pleistocene to the Pliocene fauna is a ques-. 

 tion of great difficulty. If the Pliocene fauna be compared with 

 that of the Eorest-bed, it will be seen that the difference between 

 them is very great. The Pliocene Mastodon a id Tapir, and most of 

 the Cervidas, are replaced by forms such as the Eoe and Eed Deer, 

 unknown until then ; but many of the Pliocene animals were able 

 to hold their ground against the Pleistocene invaders, although they 

 were ultimately beaten in the struggle for existence by the new 

 comers. The fauna which the author adopted as typically Pliocene 

 is that furnished by the lacustrine strata of Auvergne, the marine 

 sands of Montpellier, and the older fluviatile strata of the Yal 

 d'Arno. 



