Symonds — British Fossil Mammals. 421 



of the deposition of the Post-glacial river and sea drifts very severe, 

 and pjradually becoming temperate as we approach present times. 

 The Post-glacial Arctic Mammalia, such as the Glutton, Lemming, 

 Marmot, Musk Sheep, Elk, and Keindecr, are altogether wanting in 

 the Brick-earths of the Thames. Now it is the presence of these 

 animals that marks the Post-glacial deposits most especially. 



Tlie Glacial Epoch. — The next step carries us to the Glacial 

 epoch, the commencement of which was immensely anterior to the 

 deposition of our valley drifts and Cave-deposits. Those who choose 

 to take the trouble to follow out the reasoning and proofs adduced 

 by Sir Charles Lyell will best appreciate the overwhelming evi- 

 dence he brings to bear on the oscillations during the Glacial epoch, 

 the submergence of continents, and the conversion of continents 

 into islands ; and, again, in after periods, the reconversion of sea 

 beds into islands and continents. It was probably during the period 

 of this great gradual submergence that inch by inch, and little by 

 little, some of the great Mammalia of the Pre -glacial continental 

 period were, with the plants and shells, driven southward, and that 

 thousands perished, leaving their skeletons in the frozen drifts of 

 Siberia and the ice-caverns of the far north. It is a problem to be 

 yet solved, whether or not the Mammoth and Ehinoceros of Siberia 

 were all Pre-giacial inhabitants of those arctic regions, whose 

 descendants migrated southwards, and thus the species were pre- 

 served in temperate latitudes until Post-glacial times. It is diffi- 

 cult to believe that those animals lived in Siberia in Post-glacial 

 times, for there is little doubt that great cold existed in temperate 

 Europe for long ages after the land had assumed much the same 

 contour which it now possesses. It is not, however, my intention 

 to day, to do more than allude to the Glacial epoch, or the effect of 

 that long era of cold on the northern hemisphere. What I wish 

 to do is to impress upon my hearers the fact that the maximum 

 of intense cold did not arrive suddenly, or as a catastrophic 

 change, but approached gradually ; and was brought about by 

 physical changes of sea and land, by the elevation of highlands 

 within the Arctic circle, and, possibly, by astronomical causes 

 assisting ; also that these causes were in operation and had com- 

 menced in later Tertiary times. There have been few dis- 

 coveries of late which have so much interested geologists as 

 the discovery of the fact, through the investigation of Professor 

 Heer and other botanists, that during the Miocene epoch a rich flora 

 grew within the arctic zone, in latitudes where now only a vast 

 sheet of ice and snow extends. One hundred and sixty-two species 

 of flowering plants, forest trees, ferns, and cryptogamous plants 

 have been determined, of which no less than 128 species of woody 

 plants alone once flourished in the now icy north ; while during the 

 same period we know that in England there flourished, in the neigh- 

 bourhood of Exeter, cinnamons, vines, figs, laurels, and gigantic 

 Wellingtonias, with tree ferns and other plants, indicating a warm 

 temperature. And to these points I would especially direct attention. 

 The difference of latitude was marked distinctly in Miocene times by 



