Trof. ./. Tf. Judd — On Volcanos, 537 



In the case of the Alps I know of no glacial phenomena which 

 are not capable of being explained, like those of New Zealand, by 

 a great extension of the area of the tracts above the snow-line, which 

 would collect more ample supplies for the glaciers protruded into 

 the surrounding plains. And when we survey the grand panoramas 

 of ridges, pinnacles and peaks, produced for the most part by sub- 

 aerial action, we may well be prepared to admit that before the 

 intervening ravines and valleys were excavated, the glaciers shed 

 from the elevated plateaux must have been of vastly greater magni- 

 tude than at present. This increase of the area above the snow- 

 line, resultiug in the extension of the glaciers, would likewise 

 follow from the elevations of the whole mountain mass ; and the 

 same movement would also account for the transport of blocks across 

 the wide Swiss valley, and their lodgement on what are now opposing 

 slopes. It is an interesting confirmation of these views that the 

 Western Alps, where the subterranean action has been most violent 

 and prolonged, is also the district in which the glacial action has 

 been most powerfully marked. 



We need scarcely add that, if these views be correct, there is no 

 necessary connexion, either in their period or in their cause, between 

 the extension of glaciers in Northern Europe and the Alps respec- 

 tively. The identification of the two series of events rests indeed 

 on no sufficient palseontological or physical evidence. 



I have not in this article attempted to deal with the remarkable 

 phenomenon of the prevalence of more uniform climates over the 

 whole globe during past geological periods, the admission of which, as 

 Dana and Nordenskiold have so well pointed out, it is hardly possible 

 to avoid. This is perhaps the most difficult problem which geologists 

 are called upon at the present day to face. Possibly the results of 

 the Arctic Expedition, when fully worked out, may throw some new 

 light on this important question. 



If, in the series of articles which we are now bringing to a close', 

 we have been led to dwell at greater length upon the proofs of sub- 

 terranean action, than upon those more obvious results due to the 

 operation of external forces upon the earth's crust, it is with no 

 desire to under-estimate the importance of the latter, but rather with 

 a view to counteract the somewhat one-sided statements that have 

 been made concerning the relative effects of the two classes of terres- 

 trial forces. 



Prof. Geikie and Mr. Croll have done excellent service to geologi- 

 cal science in reviewing and calling attention to the results of 

 estimates of the amount of waste produced by subaerial denudation, 

 and the rate at which the surfaces of our existing continents are 

 being worn away. Fully agreeing with Prof. Hughes that, as actual 

 measures of geological periods, such estimates are open to so many 

 sources of error and are so difficult of application as to be worthy of 

 but little reliance, we nevertheless regard them as having a very 

 great value in enabling us to appreciate the reality and the im- 

 portant effects of operations ever going on insensibly around us. 



We venture to think that still further uses may be served by these 



