114 



ISLAND LIFE 



PART I 



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 grind- 

 ing tools, and would thus themselves become rounded, 

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

 masses would 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 

 moutonn4cs. 



The peculiar characters of the " till," its fineness and 

 tenacity, 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 when " till " is exposed to the action 

 of water, it dissolves into a similar soft, sticky, unctuous 

 mud. The present glaciers of the Alps, being confined to 

 valleys which carry off a large quantity of drainage water, 

 lose this mud perhaps as rapidly as it is formed ; but when 

 the ice covered the whole country, there was comparatively 

 little drainage water, and thus the mud and stones collected 

 in vast compact masses in all the hollows, and especially 

 in the lower flat valleys, so that, when the ice retreated, 

 the whole country was more or less covered with it. It 

 was then, no doubt, rapidly denuded by rain and rivers, 

 but, as we have seen, great quantities remain to the 

 present day to tell the tale of its wonderful formation.^ 



^ This view of the formation of "till" is that adopted by Dr. Geikie, 

 and upheld by almost all the Scotch, Swiss, and Scandinavian geologists. 

 The objection however is made by many eminent English geologists, includ- 

 ing the late Mr. Searles V. Wood, Jun., that mud ground off the rocks 

 cannot remain beneath the ice, forming sheets of great thickness, because 

 the glacier cannot at the same time grind down solid rock and yet 

 pass over the surface of soft mud and loose stones. But this difficulty 

 will disappear if we consider the numerous fluctuations in the glacier 

 with increasing size, and the additions it must have been constantly 

 receiving as the ice from one valley after another joined together, and 

 at last produced an ice-sheet covering the whole country. The grind 



