536 Trof. J. F. Judd — On Volcanos. 



Hence we are altogether spared the necessity of discussing such 

 hypothetical explanations for secular changes of climate as have been 

 advanced by Croll, Belt, Drayson, and others ; seeing that not only 

 are there no facts calling for the aid of any such hypotheses, but 

 that the conclusions of both the paleeontologist and field-geologist 

 point in quite a different direction. We are far from regretting the 

 publication of those charming works which have lately treated 

 geological questions on the hypothesis of the occurrence of a 

 rhythmical succession of hot and cold periods during the earth's 

 past history. Yet we cannot help thinking that, had their authors 

 paid a little more regard to the established results of palaeontological 

 investigation, each of the works in question might have been pre- 

 sented to the public in the form of three thin volumes rather than as 

 a single bulky one. 



Tbe distinguished geologists of New Zealand, to whom we have 

 before referred, on finding that the hypothesis of a great reduction 

 of temperature in the Southern Hemisphere was quite untenable, 

 began to search for other causes to which the former extension of 

 their glaciers could be referred. Such a cause they believe them- 

 selves to have discovered in the demonstrated former existence of 

 widely extended tracts (now reduced to narrow ridges only by 

 denudation) above the snow-line, and the maintenance of these vast 

 gathering grounds for glaciers during enormous periods of time, by 

 the subterranean movements that have so greatly aff'ected New 

 Zealand. 



Have not precisely similar causes been at work in the case of the 

 Alpine district, and are not the phenomena of the former extension 

 of glaciers in that area far more in accord with such a cause, as we 

 have just referred to, than with the hypothesis of alternations of 

 climatal condition, due to astronomical causes — even supposing that 

 these were not so distinctly negatived by paleeontological evidence ? 

 Since the incubus of the Universal Deluge was got rid of by 

 geologists, no hypothesis more obstructive to the development of 

 their science has appeared, than the doctrine that the existence of 

 ice-action in a district is a proof of secular refrigeration of climate. 



Of the various cosmical causes so ably discussed by Mr. Searles 

 Wood in recent numbers of the Geological Magazine, we may 

 readily grant that one or more may have contributed in some 

 degree to the production of variations in climate during past geo- 

 logical times ; but, until the effects of those local changes of level 

 which we know to have occurred have been fully taken into account 

 and proved to be inadequate in each special case, it is surely very 

 rash indeed on the part of geologists to appeal to agencies, of which 

 the origin and eff'ects are confessedly so little understood. And 

 while it is scarcely possible to assign a limit to the size which 

 glaciers might attain — if supplied from feeding grounds of sufficient 

 elevation and extent, on which a large amount of precipitation was 

 constantly taking place — it is very difficult indeed to understand 

 how a simple reduction of temperature should produce the effects 

 which are so constantly assigned to it by some writers. 



