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SCIENCE 



[N. S. Vol. XL. No. 1033 



folds, were formed at a late date in tlie 

 earth's history, folds which in date and 

 direction have no genetic relationship 

 to G. H. Darwin's primitive wrinkles. 

 Then, besides the folding and plication of 

 the crust in some areas, we have to account 

 for the undoubted stretching which it has 

 suffered in other places, stretching of a 

 kind indicated by faults so common that 

 they are generally known as normal faults. 

 It has been estimated by Claypole that the 

 folding of the Appalachian range resulted 

 in a horizontal compression of the strata to 

 a belt less than 65 per cent, of the original 

 breadth. According to Heim the diameter 

 of the northern zone of the central Alps is 

 not more than half the original extension 

 of the strata when they were laid down in 

 horizontal sheets. De la Beche, in his 

 memoir on Devon and Cornwall, which an- 

 ticipated many problems of more than local 

 interest, pointed out that, if the inclined 

 and folded strata were flattened out again, 

 they would cover far more ground than 

 that to which they are now restricted on 

 the geological map. Thus, according to 

 Dutton, Fisher, and others, the mere con- 

 traction of the cooling globe is insufficient 

 to account for our great rock-folds, espe- 

 cially great folds like those of the Alps and 

 the Himalayas, which have been produced 

 in quite late geological times. It is pos- 

 sible that this conclusion is in the main 

 true; but in coming to this conclusion we 

 must give due value to the number of 

 patches which have been let into the old 

 crustal envelope — masses of igneous rock, 

 mineral veins and hydrated products which 

 have been formed in areas of temporary 

 stretching, and have remained as perma- 

 nent additions to the crust, increasing the 

 size and bagginess of the old coat, which, 

 since the discovery of radium, is now re- 

 garded as much older than was formerly 

 imagined by non-geological members of the 

 scientific world. 



The peculiar nature of rock-folds pre- 

 sents also an obstacle no less formidable 

 from a qualitative point of view. If the 

 skin were merely collapsing on its shrink- 

 ing core we should expect wrinkles in all 

 directions; yet we find great folded areas 

 like the Himalayas stretching continuously 

 for 1,400 miles, with signs of a persistently 

 directed overthrust from the north; or we 

 have folded masses like the Appalachians 

 of a similar order of magnitude stretching 

 from Maine to Georgia, with an unmistak- 

 able compression in a northwest to south- 

 east direction. The simple hypothesis of a 

 collapsing crust is thus "quantitatively in- 

 sufficient," according to Dutton, though 

 this is still doubtful, and it is "qualita- 

 tively inapplicable," which is highly prob- 

 able. 



In addition to the facts that rock-folds 

 are maintained over such great distances 

 and that later folds are sometimes found 

 to be superimposed on older ones, geologists 

 have to account for the conditions which 

 permit of the gradual accumulation of 

 enormous thicknesses of strata without cor- 

 responding rise of the surface of deposi- 

 tion. 



On the other hand, too, in folded regions 

 there are exposures of beds superimposed 

 on one another with a total thickness of 

 many miles more than the height of any 

 known mountain, and one is driven again 

 to conclude that uplift has proceeded pari 

 passu with the removal of the load through 

 the erosive work of atmospheric agents. 



It does not necessarily follow that these 

 two processes are the direct result of load- 

 ing in one case and of relief in the other; 

 for slow subsidence gives rise to the condi- 

 tions that favor deposition and the uplift- 

 ing of a range results in the increased 

 energy of eroding streams. 



Thus there was a natural desire to see if 

 Dutton 's theory agreed with the variations 

 of gravity. If the ups and downs are bal- 



