110 



ISLAND LIFE. 



[part I, 



found underneath moraines, drift, and other late glacial deposits, 

 but never overlies them (except in special cases to be hereafter 

 referred to), so that it is certainly an earlier deposit. 



Throughout Scotland, where ''till " is found, the glacial striae, 

 perched blocks, roches moutonnees, and other marks of glacial 

 action, occur very high up the mountains to at least 3,000 and 

 often even to 3,500 feet above the sea, while all lower hills and 

 mountains are rounded and grooved on their very summits ; 

 and these grooves always radiate outwards from the highest 

 peaks and ridges towards the valleys or the sea. 



Inferences from the Glacial Phenomena of Scotland. — Now all 

 these phenomena taken together render it certain that the 

 whole of Scotland was once buried in a vast sea of ice, out of 

 which only the highest mountains raised their summits. There 

 is absolutely no escape from this conclusion ; for the facts which 

 lead to it are not local — found only in one spot or one valley — but 

 general throughout the entire length and breadth of Scotland ; 

 and are besides supported by such a mass of detailed corrobo- 

 rative evidence as to amount to absolute demonstration. The 

 weight of this vast ice-sheet, at least three thousand feet in 

 maximum thickness, and continually moving seaward with a 

 slow grinding motion like that of all existing glaciers, must have 

 ground down the whole surface of the country, especially all the 

 prominences, leaving the rounded rocks as well as the grooves 

 and striae we still see marking the direction of its motion. All 

 the loose stones and rock-masses which lay on the surface would be 

 pressed into the ice ; the harder blocks would serve as scratching 

 and grinding tools, and would thus themselves become rounded, 

 scratched, and striated as we see them, while all the softer masses 

 w^ould be ground up into impalpable mud along with the 

 material planed off the rocky projections of the country, leaving 

 them in the condition of roches moutonnks. 



The peculiar characters of the ''till," its fineness and tena- 

 city, correspond closely with the fine matter which now issues 

 from under all glaciers, making the streams milky white, 

 yellow, or brown, according to the nature of the rock. The 

 sediment from such water is a fine unctuous sticky deposit, 

 only needing pressure to form it into a tenacious clay ; and 



