September 3, 1914] 



NATURE 



13 



the eastern ice-sheets would thus have been active 

 within 30° of Prof. Koken's Permian equator. There 

 are still three other serious pieces of colour-discord 

 in this picture. In the State of Sao Paulo — that is, 

 within Koken's "Permian" tropics — Dr. Orville 

 Derby has described beds which strikingly recall the 

 features of the Upper Palaeozoic glacial beds of India 

 and South Africa. It is possible that these are due 

 to the work of glaciers at a high level ; but, since 

 the publication of Prof. Koken's memoir, other occur- 

 rences of the kind have been described by Dr. I. (7. 

 White in different parts of Brazil, and there is a 

 general correspondence between the phenomena in 

 South America and those in the formations of the 

 same age in the Indian, Australian, and African 

 regions. 



Then, too, if we accept this expression of the 

 physical geography during Upper Palaeozoic times, 

 we must carefully explain away the suspicious breccias 

 and brockrams which have been regarded by many 

 geologists as evidences of a cold climate during 

 Permian times in the Urals, the Thiiringerwald, the 

 English midland and northern counties, Devonshire 

 and Armagh — places that would lie on or near 

 Koken's "Permian" equator. Finally, we find the 

 hypothetical Permian North Pole in a locality which 

 has Tailed to produce any signs of glaciation. 



To attempt a discussion of the explanations offered 

 to account for the great Upper Palaeozoic glaciation 

 would lead us far from the present theme. The 

 question Is raised merely to show that the phenomena 

 are not consistent with the supposed movement of a 

 solid shell over a solid core assisted by an inter- 

 mediate molten lubricant. Geologists may be com- 

 pelled to hand back the theory of a molten substratum 

 to the mathematicians and physicists for further 

 repair; but it does not necessarily follow that a foun- 

 dation theory is unsound merely because it has been 

 overloaded beyond its compressive strength. 



The extraordinarily great distances between the 

 areas that show signs of glaciation in Permo-Carbon- 

 iferoiis times form a serious stumbling-block to most 

 of the explanations which have hitherto been offered. 

 One is almost tempted in despair even to ask if it 

 is not possible that these fragments of the old Gond- 

 wana continent are now more widely separated from 

 one another than they were in Upper Palaeozoic times. 

 It is a bold suggestion indeed that one can safely put 

 aside as absurd in geomorphology. There is nothing 

 else apparently left for us but the assumption of a 

 general refrigeration. 



The idea of the greater inequalities of the globe 

 being in approximately static equilibrium has been 

 recognised for many years : it was expressed by 

 Babbage and Herschel ; it was Included In Arch- 

 deacon Pratt's theory of compensation ; and It was 

 accepted by Fisher as one of the fundamental facts 

 on which his theorv of mountain structure rested. 

 But in 1889 Captain C. E. Dutton presented the Idea 

 "In a modified form, in a new dress, and In greater 

 detail " ; he gave the Idea orthodox baptism and a 

 name, which seems to be necessary for the respectable 

 life of any scientific theory. " For the condition of 

 equilibrium of figure, to which gravitation tends to 

 reduce a planetary body. Irrespective of whether it be 

 homogeneous or not," Dutton ^' proposed " the name 

 x5osfasy." The corresponding adjective would be 

 Isostatic — the state of balance between the ups and 

 downs on the earth. 



For a long time geologists were forced to content 

 themselves with the conclusion that the folding of 

 strata is the result of the crust collapsing on a cooling 



1* Dutton, "On Some of the Greater Problems of Phyiical Geology," 

 Bull. Phil. Soc. Wash., x!., 53, 1889. 



NO. 2340, VOL. 94] 



and shrinking core; but Fisher pointed out that the 

 amount of radial shrinking could not account even 

 for the present great surface inequalities of the litho- 

 sphere, without regard to the enormous lateral 

 shortening indicated by the folds in great mountain 

 regions, some of which, like the Himalayan folds, 

 were formed at a late date in the earth's history, folds 

 which in date and direction have no genetic relation- 

 ship 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 Ap- 

 palachian 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 

 anticipated 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 contraction of the cooling 

 globe is insufficient to account for our great rock-folds, 

 especially great folds like those of the Alps and the 

 Himalayas, which have been produced In quite late 

 geological times. It Is possible 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 tem- 

 porary stretching, and have remained as permanent 

 additions to the crust, Increasing the size and baggi- 

 ness of the old coat, which, since the discover}- of 

 radium. Is now regarded as much older than was 

 formerly Imagined by non-geological members of the 

 scientific world. 



The peculiar nature of rock-folds presents also an 

 obstacle no less formidable from the qualitative point 

 of view. If the skin were merely collapsing on Its 

 shrinking core we should expect wrinkles in all direc- 

 tions; yet we find great folded areas like the Hlma- 

 lavas stretching continuously for 1400 miles, with 

 signs of a persistently directed overthrust from the 

 north ; or we have folded massss like the Appalachians 

 of a similar order of magnitude stretching from 

 Maine to Georgia, with an unmistakable compression 

 in a north-west to south-east direction. The_ simple 

 hypothesis of a collapsing crust is thus " quantitativelv 

 iiisuflScIent," according to Dutton, though this Is still 

 doubtful, and it is "qualitatively inapplicable," which 

 is highlv probable. 



In addition to the facts that rock-folds are main- 

 tained 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 corresponding 

 rise of the surface of deposition. 



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 anv known mountain, and one is driven 

 again to conclude that uplift has proceeded ^ari passu 

 with the removal of the load through the erosive 

 work of atmospheric aeents. 



It does not necessarily follow that these two pro- 

 cesses are the direct result of loading in one case and 



