J, W. Judd — On Volcanos. 13 



certain facts, which are altogether inexplicable by and opposed to 

 the theory of the excavation of rock-basins by ice — namely, the 

 frequent absence of lakes in certain other glaciated regions and in 

 situations where, according to that theory, the conditions were most 

 favourable for their production. If, as we maintain, the formation 

 and preservation of numerous lake-basins in a district is due to a 

 favourable coincidence of subterranean movement with the suspension 

 of the obliterating effects of river denudation through the occurrence 

 of glacial conditions at the surface, then the abundance of such lakes 

 in some glaciated regions and their paucity in others are alike ac- 

 counted for. 



It is, however, impossible to conceal from ourselves that the real 

 obstacle to the reception of so simple an explanation of the formation 

 of lake-basins, as that afforded by local changes of level due to dif- 

 ferential subterranean movements along lines of drainage, and the 

 consequent appeal to the hypothetical agency of the excavating 

 power of ice, is the strange assumption that the production of the 

 features of the earth's surface is entirely due to the action of denud- 

 ing agents, and that subterranean forces have played no j)art whatever 

 in the matter. We cannot but regard this doctrine — so boldly advanced 

 by several modern writers on geology — as opposed to the fundamental 

 and best established principles of the science, and as being not less 

 mischievous in its tendencies, than it is unsupported by facts. 



That differential movements of the most striking character have 

 taken place in the earth's crust during every geological period, no 

 one who examines the admirable detailed maps of the Geological 

 Survey of the United Kingdom, and studies the effects produced by 

 the numerous faults indicated upon them, can for one moment doubt. 

 And yet every practical geological surveyor will readily admit that 

 the dislocations of the strata, which he is able to detect, bear prob- 

 ably only a small proportion to those which actually exist. This 

 is shown by the fact that while in formations exhibiting rapid alterna- 

 tions of thin beds, like the Coal Measures or the Oolites, in which 

 faults are easily detected, they are represented as exceedingly 

 abundant, in others, consisting of uniform masses like Mountain 

 Limestone, Lias Clay or Chalk, where it is difficult to trace their 

 effects, but very few are indicated. But even where no actual 

 fractures of the strata occur, undulations and foldings of various 

 degrees of curvature bear witness to the continual action of sub- 

 terranean forces. And that the effects of these were felt at the 

 surface is amply demonstrated by peculiarities in the mode of 

 accumulation of the various sediments, which, as Darwin has so 

 well shown, must ever be dependent on the rate of subsidence. Nor 

 have we the smallest grounds for believing that these subterranean 

 movements and the effects produced by them at the surface are one 

 whit less powerful at the present time than during former geological 

 periods. In proof of this we need only point to the numerous facts 

 that have been accumulated, especially by Lyell and Darwin, show- 



tlie Scandhiavian and North American regions, which exhibit such a vast number of 

 lakes, we have unmistakable proofs that considerable movements of the sui'face of 

 the land have been going on in comparatively recent times. 



