130 ANNALS OF SCOTTISH NATURAL HISTORY 



cerned, even if it were admitted that in other parts of the 

 globe man had been on the earth during Tertiary times, 

 there is little likelihood that his remains could have been 

 preserved ; for in that country the Tertiary is represented 

 chiefly by volcanic rocks, and a few patches of sand and 

 gravel with rolled sea shells belonging to the closing stages 

 of that period. 



From the careful study which geologists have given to 

 the surface of Scotland, it is evident that at the commence- 

 ment of the period termed Quaternary or Pleistocene, 

 immediately succeeding the Tertiary, the whole of the 

 country was covered with ice which formed a great sheet 

 3000 or 4000 feet thick in the low grounds, of which the 

 lower boulder clay, or till, as it is termed, was the ground- 

 moraine. 



As an upper boulder clay also occurs, which is often 

 separated from the lower boulder clay by stratified deposits, 

 some of which contain marine and other fresh- water and 

 terrestrial organic remains, it is obvious that the Ice Age 

 was not one uninterrupted period of continuous cold. 1 The 

 lower and upper tills are the ground-moraines of independent 

 ice sheets, each indicating a distinct epoch, separated by an 

 interglacial period. The earlier epoch was that of maximum 

 o-laciation, and the ice sheet extended over the north and 



o 



middle of England, as far south as the Thames valley and 

 the foot of the Cotswold Hills, but the high moors in Derby- 

 shire and Yorkshire and the tops of the highest mountains 

 in Wales and Scotland rose above its surface. The great 

 Mer de Glace stretched westward over Ireland into the 

 Atlantic, whilst on the east it was continuous across the 

 North Sea, with a similar ice sheet which covered 

 Scandinavia and the region of the Baltic, and extended 

 south to the foot of the hills of central Europe, and over- 

 spread much of the great central plain. In the extreme 

 south of England, therefore, the conditions differed from 

 those that obtained in the country farther north. Although 

 not actually covered with a sheet of ice, yet the more 



1 For the evidence on which these statements are based, consult the " Great 

 Ice Age," by Professor James Geikie, edition 1894, also his 'Classification of 

 European Glacial Deposits,' in "Journal of Geology," vol. iii., April-May 1895. 



