The Heology of the Cluden Basin. 133 



full sur\-ey of the breccia had better he left to a future paper, 

 dealing with a larger district. 



We come now to the second part of the paper, which deals 

 with the superficial deposits and their recent denudation, both of 

 which conclusively dominate our scenery. This brings us to the 

 Glacial Period during the Pleistocene Age. Between it and the 

 Tri?ssic sandstones an interval had elapsed sufficient to permit 

 the formation of 8000 or 9000 feet of younger strata in England. 

 Towards the close of the Pliocene Age the temperature of the 

 whole northern hemisphere gradually fell, while the land was 

 being elevated considerably above its present level. The Sohvay 

 Firth and the Irish Channel were converted into grassy plains. 

 The cold increased, until tinally Arctic conditions prevailed. 

 Many of the large animals died; the mammoth and others 

 migrated south ; while a few, such as the woolly rhinoceros, were 

 able to adapt themsehes to the more rigorous conditions by a 

 growth of wool. The whole of Scotland was covered by an 

 immense accumulation of snow, which continued to increase until 

 in the highest lands great sheets of ice were formed. The moun- 

 tainous region of Galloway towards Merrick and the Kells formed 

 a centre of dispersion for this extensive ice sheet, which radi- 

 ated from the Gallowa}- snow-field in all directions, and mo^•ed 

 slowly, yet irresistibly, to lower levels. During this period of 

 extreme cold our highest hills were overridden by the moving ice. 

 When crossing the Irongray and Speddoch hills the glaciers 

 travelled east and south-east, as indicated by the strije upon the 

 rocks and other indisputable proofs. The enormous pressure of 

 a moving ice sheet 1000 feet thick had a wonderful effect in trans- 

 forming all angularities into rounded, smoothed, and dressed 

 rock surfaces. These roches moutonnees are as pronounced as 

 those of Norway or the Alps amidst existing glaciers. Eventu- 

 ally the land sulisided gradually until the sea rose to a height of 

 100 feet above its present level. This was maintained for some 

 considerable time, allowing a notch or platform to be carved in 

 the cliffs by the waves, and a sea beach or marine terrace to be 

 deposited in the estuaries. A re-elevation of the land now set 

 in, until the 50 feet contour was reached, when another pause 

 took place and another terrace was formed. This was towards 

 the close of the Ice Age, and represents the most interesting 

 period in relation to the scenery. The glaciers had now become 



