J. Clifton Ward — Modern Vulcanicity. 39 



poured forth over all." Such products, which the author says are 

 '•commonly called plutonic," he distinguishes from those of the 

 volcano by being "not explosive." 



Does it not seem that Mr. Mallet is here making a difference 

 between action from below in the early . stages of geologic history 

 and that action in modern and recent geologic times which does not 

 exist in fact? 1 Volcanic products, both sub-marine and sub-aerial, 

 of the most unmistakable character, occur in rocks of all ages down 

 to the base of the Lower Silurian. Basaltic lavas, in which the 

 component minerals seem to have crystallized in the very same 

 order and under the same conditions as in modern flows, have now 

 been traced back to periods of the world's history before, apparently, 

 vertebrate life came into existence, and when the very ancient order 

 of Graptolites flourished. There is nothing to mark the old sub- 

 aerial volcanic products of Cumbria, and the sub-marine volcanic 

 products of Snowdonia, from those of recent sub-aerial or sub-marine 

 volcanos, except the metamorphism which the older rocks have been 

 inevitably subject to, but which has seldom succeeded in obliterating 

 their original character as a whole. There would seem to be as 

 little doubt that ' Vulcanicity ' presented phenomena of an ' explosive ' 

 character, characteristic of the volcano, in the English Lake- district 

 during the middle of the Lower Silurian, as that such phenomena 

 now occur on the shores of the Bay of Naples. 



But, if this be so, since our geologic history is, properly speaking, 

 bounded by the lowermost of known sedimentary formations, it 

 surely is not safe to say that there is any essential difference between 

 modern 'Vulcanicity' and that which prevailed at the earliest stages 

 of the Earth's history. 



Let us now examine a little into the truth of Mr. Mallet's suppo- 

 sition that "the great masses of the mountain-chains were elevated" 

 during the "earliest stages " of Vulcanicity. He evidently regards it 

 as unlikely that great movements of elevation and depression ai*e 

 now taking place, such as result in the formation of mountain chains 

 or in the depression of such beneath the waters of the ocean, although 

 he does not deny that such chains " may be possibly increasing in 

 stature year by year, or at times ; but in any case at a rate almost 

 infinitesimally small in its totality over the whole earth to that with 

 which their ridges were originally upreared." (p. 63 op. cit.) 



Are there, however, any legitimate reasons for supposing that the 

 movements of elevation and depression were in the earlier course of 

 geologic history more rapid and sudden than at present ? Is there 

 any evidence, for instance, that in times so far back as the Silurian, 

 great elevations or depressions of land took place at all rapidly ? 

 Can we with any show of truth assign the origin of the leading 

 chains of mountains to the earliest geologic ages? To answer these 

 questions aright, we must consider denudation as well as upheaval 

 and depression. Prof. Ramsay has shown that in Wales the many 

 thousand feet of strata formed during the Lower Silurian period were 

 upraised, contorted, cleaved, and extensively denuded before the 

 1 See also Mr. Scrope's criticism in Geol. Mag. January, 1874, page 3L. 



