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



agents of the greatest importance in modifying the physical 

 features of the countries in which they exist on a large scale. 

 The Himalayan mountains and the mountains of New Zealand 

 haye been found to exhibit these phenomena on a grand scale. 

 In the former one glacier alone has a length of 86 miles, more 

 than three times that of any existing Alpine glacier ; but in 

 the Alps themselves, on the Italian side, there is proof of the 

 former existence of ice streams, one of them 50 miles in length, 

 and others even more. The hills throughout the valley of the 

 Po are mere remains of old moraines left behind by the gla- 

 ciers of the south side of the Alps. 



But glaciers combine in some measure the properties of 

 solids and fluids. They are solid and hard, and exceedingly 

 heavy; and being loaded frequently with hard rocks and stones 

 throughout their mass, they grind powerfully the rocks over and 

 between which they pass. Being in a state in which the parts 

 move on each other, they flow in a certain sense, adapting 

 themselves to all the inequalities of the channel through which 

 they pass, and in this respect moving like thick tenacious 

 fluids, such as treacle. They can certainly exert an eroding 

 and excavating and polishing force on the rocks they cross, 

 and this to an enormous extent ,- so that the water coming 

 from them is loaded with mud, and their surface is covered 

 with stones and rocks that they have in their progress torn 

 away or ploughed up. 



Now, the view of the younger school of geologists is that 

 the whole present configuration of mountain chains, the valleys 

 and even the rock-basins now filled with fresh water and form- 

 ing lakes, as well as the outline of the hills and plains over the 

 whole continent of Europe, Asia, and North America, are really 

 due not to any rapid disruption and thrusting up of hard rock 

 into the air through the more modern stratified deposits, but 

 to a very slow elevation, accompanied by much hard squeezing, 

 and by very great denudation, erosion, and excavation ; the 

 whole of these latter results having been produced either by 

 water, when at first the elevation was small, or by ice when 

 it became considerable, and when glaciers in their progress 

 towards the sea either filled the valleys that were already 

 formed, or scooped out other valleys by their own eroding 

 power. 



There is no doubt that the work thus defined is very 

 gigantic, and that the time needed for such work must have 

 been extremely great. But, in the present state of geological 

 science, it is admitted that time is absolutely demanded to 

 account for all classes of phenomena. The evidence must bo 

 weighed and estimated according to its real value ; and so far 

 as the Alps are concerned, there is much evidence that has only 

 recently been obtained whose value is very grcni. 



