Influence of Water and Ice on the Earth's Features. 355 



inclined to take for granted the further assumptions of those 

 who adopt the fracture theory. It is easy to believe,, with 

 these facts before us, that all valleys that are deep and strongly 

 marked are valleys of elevation or fault valleys, and that lakes 

 occupy the depressions caused by the slipping down and falling 

 in of strata, or the removal of rocks broken during the convul- 

 sive throes of a great upheaval. We see in imagination a 

 fearful disruption and a rending of the solid crust of the earth ; 

 wide and deep fissures are produced, granite is thrust up 

 through the softer and more yielding shales, clays, sands, and 

 limestones ; the whole form of the mountain chain and all its 

 details are determined by the first elevation, and the continued 

 thrusts upwards in the same direction are all subordinate. 

 Each thrust upwards is an epoch, and rest must follow each 

 effort. At length there results a chain like the Alps, present- 

 ing every variety of form ; and the chain, once formed, must, 

 we imagine, remain quite unaltered for ages. 



It is a good many years since Agassiz, followed by some 

 other bold speculators in geology, ventured to suggest that the 

 glaciers that now lazily creep down certain mountain valleys of 

 (Switzerland are but the puny remains of other glaciers that 

 once crossed the whole of the fertile valley of Switzerland from 

 the Alps to the Jura, and that covered much land elsewhere in 

 Europe and North America. He insisted that there was a 

 period — not very long ago, speaking geologically — when huge 

 rivers of ice covered the land, when great icebergs drifted 

 through the sea that surrounds our shores, and when all the 

 surface gravel that abounds in the northern hemisphere was 

 being formed and deposited and transported by ice and water. 

 This startling hypothesis, as it once seemed, is already a part 

 of the alphabet of geology. We speak of the glacial period 

 with as much certainty as if its history had come down by 

 human tradition. No one hesitates to admit that the striations 

 and scratches in rocks, under and near gravel, are the results 

 of the passage of ice; and the whole subject of the influence of 

 ice is admitted as far as gravel is concerned. 



Much more recently views have been put forward which 

 may seem quite as startling as those connected with glaciers 

 did to the geologists of a former day when they were first pre- 

 sented. These views are opposed vehemently, and even bit- 

 terly, by some of our very eminent geologists, and even by 

 some of those who fully admit that glaciers have transported 

 huge blocks of crystalline rock across Switzerland. But they 

 are views that have already received very powerful advocacy, 

 and they are daily acquiring fresh importance. 



The more carefully and minutely the evidence has been in- 

 vestigated, the more clearly has it appeared that glaciers are 

 VOL. vi. — no. v. A A 



