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DYNAMICAL GEOLOGY. 



On the west side of the Appalachian geosynclinal no similar geanticlinal was formed 

 in the Paleozoic era; for marine fossilliferous beds were in progress there, in alternation 

 with peat-beds for coal-making, all through the Carboniferous period. 



These conditions just stated involve the following successive steps 

 in the mountain-making process : — 



(3.) The bottom of the geosynclinal becomes weakened by the heat 

 rising into it from below. The accumulation of sedimentary beds 

 would occasion, as Babbage long since urged, a rising of heat from 

 below, so that, with 40,000 feet of such accumulations, a given isogeo- 

 thermal plane would have been raised, neglecting secular cooling, 

 about 40,000 feet. Under such an accession of heat, the bottom of 

 the trough would have been, as Herschel recognized, greatly weak- 

 ened, if not partly melted off. 



The heat in the lower part of the trough is only slightly increased, 

 if at all, by the transformation of motion into heat. The heat thus 

 derived would be feeble in amount if the motion were extremely slow 

 and regular. With fractures, shovings, and crushing accompanying 

 it, the heat from the rise of the isogeothermal might have been much 

 reenforced ; but proof that such fractures, shovings, and crushings have 

 occurred before the final catastrophe, usually fails. In the Wahsatch 

 trough the beds at the bottom of the 60,000 feet still have their fossils 

 distinct, or show only slight evidences of change. (King.) 



(4.) The weakened trough yields before the pressure, in a fracture 

 of the trough below, and some pressing together of the stratified beds 

 within it. And with this break the shaping of the mountain begins. 



Herschel, in a letter addressed to Lyell, dated February, 1836, and in another to 

 Murchison, dated November, 1836, which are published in the Appendix to Babbage's 

 " Ninth Bridgewater Treatise " (1837), presents the view that heat will rise from below 

 into an accumulating series of strata, as had been done by Babbage, and also the hy- 

 pothesis that subsidence of the earth's crust will be a consequence of the weight of the 

 strata; and says, on the former point, "the thicker the deposit, the hotter will its lower 

 portions tend to grow, and if thick enough they may grow red-hot, or even melt. In the 

 latter case, their supports, being also melted or softened, may wholly or partially yield 

 under the new circumstances of pressure, to which they were originally not adjusted; 

 and the phenomena of earthquakes, volcanic explosions, etc., may arrive, while, on the 

 other hand, if no cracks occur and all goes on quietly, the only consequence will be 

 .... in a word, the production of Lyell's metamorphic rocks." Dr. T. Sterry Hunt, 

 in a paper on mountains, adopts the views of Herschel as to the cause of the subsid- 

 ence and the rising of heat from below, and adds that the lines of weakness being 

 established by the softening of the bottom strata through the heat received from be- 

 low, "would determine the contraction which results from the cooling of the globe to 

 exhibit itself in those regions and along those lines where the ocean is subsiding be- 

 neath the accumulating sediments." 



(5.) The stratified rocks become, in the partial collapse, upturned 

 or folded, and pressed into a narrower space than they occupied be- 

 fore, much fractured and faulted ; and finally — for such processes 

 move on slowly — a mountain range exists as the result. The crust 



