344 J. W. Judd^On Volcanos. 



only a subordinate effect in producing the actual forms of the Alpine 

 masses. 



Of the last grand elevation of the masses of crumpled and crystal- 

 lized sediments, out of which the Alpine peaks and valleys have been 

 sculptured, we have apparently a striking proof in the former pre- 

 valence of glaciers of enormous extent, descending from them into 

 the plains around. Some have seen in these indications only the 

 evidences of a former period of intense cold, or even of a succession 

 of such periods. But if we consider that one of the main requirements 

 for the production of vast glaciers is the existence of a large area of 

 precipitation above the snow-line of the district, we shall be led to 

 conclude that the upheaval of the gigantic Alpine masses during the 

 Miocene would be just such a cause as would produce the phenomena 

 in question. And as the broad ridge was gradually eaten a,wsij on 

 either side, in the manner so graphically described by Dr. Hector as 

 haviug taken place in New Zealand — atmospheric forces crumbling 

 the storm-beaten rocks, while the ever- descending glacier bore the 

 detritus into the valleys, thus constantly exposing fresh surfaces — 

 the great continuous plateau would gradually be broken up and 

 assume the form of isolated peaks and ridges, separated by valleys. 

 Finally, as the gathering grounds of the Alpine snows were gradu- 

 ally reduced in extent, the glaciers which they fed would also be 

 diminished, and the transporting power of running water be sub- 

 stituted for that of moving ice. 



The deposits on the lower lying tracts around the Alps certainly 

 point rather to the existence of a tropical or sub-tropical district, into 

 which glaciers bearing transported blocks were protruded, owing to 

 the existence of a large area in the vicinity above the snow-line, 

 than to that constant change of temperature of the whole hemisphere, 

 which some have argued for, but which is negatived by so much 

 palseontological evidence. The great point which is constantly lost 

 sight of by these theorists is that the existence of glacial conditions 

 is no proof whatever of a reduced temperature in a district, but only 

 of the presence in the neighbourhood of a large extent of land 

 subject to great precipitation of moisture above the snow-line. 

 In New Zealand and South America the rocks are being scored and 

 striated, and accumulations of glacial detritus are being formed 

 in the midst of a district covered with tree-ferns and surrounded 

 by a tropical or sub-tropical fauna and flora ; and in the Jurassic 

 period a similar state of things prevailed in our own islands. That 

 the peculiarities of the deposits of the Miocene and subsequent 

 periods which surround the Alps are much more easily accounted 

 for by the phenomena we have alluded to, rather than by invoking 

 the aid of great secular changes in the climate of the globe, due to 

 very questionable astronomical causes, most geologists will be pre- 

 pared to admit ; though of course changes of climate due to the 

 different distribution of land and water, and perhaps also to other 

 causes less perfectly understood, would certainly have had a place 

 in the Alpine as well as in other districts. 



That the earth's crust presents evidence, as Prof. Suess has so well 



