384 Mr. J. Croll on Geological Ti?ne } and the probable 



of the climate during the period in question, what would pro- 

 bably be the conclusion at which he would arrive? He would 

 probably find here and there patches of boulder-clay containing 

 striated and ice-worn stones. Now and again he would meet 

 with bones of the mammoth and the reindeer, and shells of an 

 Arctic type. He would likewise find huge blocks of the older 

 rocks imbedded in the formation, from which he would infer 

 the existence of icebergs and glaciers reaching the sea-level. 

 But, on the whole, he would find that the greater portion of 

 the fossil remains met with in this formation implied a warm and 

 temperate condition of climate. At the lower part of the for- 

 mation, corresponding to the time of the true boulder-clay, 

 there would be such a scarcity of organic remains that he 

 would probably feel at a loss to say whether the climate at 

 that time was cold or hot. But if the intense cold of the 

 glacial epoch was not continuous, but was broken up by one 

 or more warm periods*, during which the ice, to a conside- 

 rable extent at least, disappeared for a long period of time (and 

 there are few geologists who have properly studied the sub- 

 ject that will positively deny that such was the case), then the 

 country would no doubt during those warm periods possess an 

 abundance of plant and animal life. It is very probable that it 

 was during those periods that the Arctic forests flourished. It is 

 quite true that we may almost search in vain on the present land- 

 surface for the organic remains which belonged to those intergla- 

 cial periods ; for they were nearly all swept away by the ice which 

 followed. But no doubt in the deep recesses of the ocean, 

 buried under hundreds of feet of sand, mud, clay, and gravel, 

 lie multitudes of the plants and animals which then flourished 

 on the land, and w r ere carried down by rivers into the sea. 

 And along with these lie the shells and other marine faunas 

 which flourished in the warm seas of those periods. A geo- 

 logist, thus judging from the great abundance of organic re- 

 mains that this lower portion of the formation would contain 

 indicating a warm condition of climate, and the almost total 



* For geological evidence of warm periods during the glacial epoch, 

 see : — Mr. Geikie's memoir '* On the Glacial Drift of Scotland ; " M. 

 Morlot "On the Posttertiary and Quaternary Formations of Switzerland," 

 Edin. New Phil. Journ., New Series, vol. ii. 1855 ; Lyell's 'Antiquity of 

 Man/ p. 321, second edition; ' Principles/ vol. i. p. 198, tenth edition ; 

 Heer, Urwelt der Schweiz ; Vogt's ' Lectures on Man/ pp. 318-321 ; Mr. 

 Edward Hull " On the Drift-deposits in the Neighbourhood of Manches- 

 ter," Mem. Lit. and Phil. Soc. of Manchester, 1863. For some remarkable 

 facts bearing on the subject, see a valuable memoir by Mr. James Bennie 

 of Glasgow, " On the Surface Geology of the District round Glasgow," 

 Trans, of the Geol. Soc. of Glasgow, vol. hi. part 1. See also a paper by 

 Mr. James Geikie " On the Remains of the Bos primigenius found in an 

 Interglacial Bed," Gcol. Mag. for September 1868. 



