12 



NATURE 



[September 3, 1914 



btiHn '- thus explains the general prevalence of basic 

 lavas in oceanic volcanoes. 



The apparent heterogeneity indicated in the outer 

 shell of the earth to depths of looo miles is naturally 

 in conflict with the assumption that from thirty miles 

 or so down the materials are in a liquid condition ; at 

 any rate, the idea conflicts with Fisher's extreme con- 

 ception of the liquid substratum, in which the fluidity 

 is supposed to be sufficient for the production of con- 

 vection currents, upwards beneath the oceanic depres- 

 sions, spreading horizont-i'ly towards the continents, 

 and thence downwards to complete the circuit. 



The idea that changes of azimuth and of latitude 

 may be brought about by the sliding' of the earth's 

 crust over its core has been put forward more than 

 once to account for the climatic changes of past 

 geological ages — the occurrence of temperate or even 

 warm climates on parts of the crust now within the 

 polar circles, and glacial conditions at the sea-level 

 in countries like India, Australia, Africa, and South 

 America, which are now far from the polar ice-sheets, 

 and in some cases near or within the tropics. Prof. 

 E. Koken, of Tubingen," in an elaborate memoir 

 entitled " Indisches Perm und die Permische Eiszeit," 

 attributes the idea of a sliding crust to Mr. R. D. 

 Oldham ; but a similar suggestion was put forward by 

 the late Sir John Evans twenty years before the pub- 

 lication of Mr. Oldham's paper, ^' and when the theory 

 was restated in more precise form, ten years later,'' 

 it was subjected to mathematical criticism by J. F. 

 Twisden, E. Hill, and O. Fisher." 



Sir John Evans sugfjested that this movement of 

 the crust was inevitable as a consequence of the 

 moulding of the orographical features and consequent 

 redistribution of weights ; but Twisden came to the 

 conclusion that the rearrang^ement of the great in- 

 equalities on the earth's surface would be insufficient 

 to produce any appreciable sliding of the order re- 

 quired to make material differences in the climate of 

 any place. 



Oldham, "^ who was writing at the time in the field 

 in India and thus away from literature, put forward 

 the idea in i8S6 as an independent thought, and made 

 use of Fisher's new theory regarding the existence 

 of a fluid stratum between the solid crust and the 

 supposed solid core to account for the shifting of 

 places relative to the axis of rotation from the equa- 

 torial reg^ion even to the polar circles. Oldham directed 

 attention to the recorded small changes of latitude 

 at certain observatories and to the probable changes 

 of azimuth in the Pyramids of Egypt — evidences of 

 a kind which have since been greatly enlarged by the 

 work of Sir Norman Lockyer and others. 



The movements assumed to have taken place during 

 the human period are of course small ; and to project 

 from them changfes as great as the transfer of lands 

 from the polar circle to the tropics has the objection 

 that characterises a surveyor's use of "unfavourable" 

 triangles in a trig^onometrical survey. Before admit- 

 ting:, therefore, that these small chang^es of latitude 

 and of azimuth may be classed with the palaeo- 

 glacialists' evidence as data of the same kind, thougfh 

 so utterly different in magnitude, it is desirable 

 brieflv to examine the geological evidence regarding 

 past ice-ages in extra-polar areas. 



12 " Geology," ii. 1906, p. 120. 



1' N. Jahrb. fur. Min. u. s. w., igo7. 537. 



14 J. Evans, " On a Possible Geological Cause of Changes in the Position 

 of the Axis of the Farth's Crus'," Proc. Roy. Soc, xv. 46 (1866). 



15 J. F.vrns, Presidential Address, Pmc. Geo). Soc, 1876, p. 105. 



16 J. F. Twisdi-n, "On Possible Displacements of the Earth's Axis of 

 figure produced by Elevations and Depressions of her Surface," Quart. 

 Journ. Geol. Soc, .\xxiv. 35 (1S77). E. Hill, " On the Possibility of 

 Changes in the Earth's Axis," Geol. Afag., 1878, 262 and 479. O. Fisher, 

 " On the PossiUility ot Changes in the Latitude of Places on the Earth's 

 Surface," Geol. Maf^., 1878, pp. 291 and 551. 



i'^ Geol. Mag., 1886, 304. 



NO. 2340, VOL. 94] 



From the records of ancient glaciations we might 

 omit those of the pre-Cambrian rocks of North Ontario, 

 and the pre-Upper Cambrian of Norway, as these 

 areas are nearer the poles than many places which 

 were certainly covered with ice-sheets during the 

 youngest, or often so-called Great, Ice Age. But 

 besides these we have evidence of glaciation in the 

 Cambrian or possibly pre-Cambrian rocks of South 

 Australia at a latitude of 35° or less ; in South Africa 

 there were two or more distinct glacial periods before 

 Lower Devonian times in slightly lower latitudes ; 

 while in China similar records are found among rocks 

 of the Lower Cambrian, or possibly of older age, at 

 a latitude of '\i° N. 



The glacial boulder-beds found at the base of our 

 great coal-bearing system in India belong to the same 

 stratigraphical horizon as the glacial beds found in 

 South Africa, certain parts of Australia, and in parts 

 of Brazil and Sao Paulo near or within the southern 

 tropic. 



These glacial beds are often referred to in geological 

 literature as Permo-Carboniferous in age ; but Prof. 

 Koken regarded the formation in India as Permian. 

 Other valuations of palaeontological evidence, similar 

 to that relied on by Prof. Koken, place these beds 

 at a distinctly lower horizon in the European strati- 

 graphical scale, and recent work by officers of the 

 Geological Survey of India in Kashmir tends to con- 

 firm this latter view ; we now regard the base of our 

 great coal-bearinp- svstem in India — the horizon of 

 the glacial-boulder-beds — as not much, if at all, 

 younger than the Upper Coal Measures of Britain.'* 

 The precise age of the horizon is not very important 

 for our present consideration : the important point is 

 that in or near Upper Carboniferous times a wade- 

 spread glaciation occurred throughout the area now 

 occupied by India, Australia, and South Africa. The 

 records of this great glaciation are thus found stretch- 

 ing northwards beyond the northern as well as 

 southwards beyond the southern tropic. 



Now, on the assumption that the cold climate in 

 this region was due to a movement of the crust over 

 the nucleus. Prof. Koken has produced an elaborate 

 map of the World, showing the distribution of land 

 and sea during the period, with the directions of 

 ocean-currents and of ice-sheets. The Permian South 

 Pole he places at the point of intersection of the 

 present 20th parallel S. and Soth meridian E.— that 

 is, at a point in the Indian Ocean about equidistant 

 from the* glaciated regions of India. Australia, and 

 South Africa. The Permian North Pole is thus forced 

 to take up Its position In the centre of Mexico, while 

 the Equator strikes through Russia, Italy, West 

 Africa, down through the South Atlantic and round 

 bv Fiji to Vladlvostock. 



The very precision of this map reduces the theory 

 on which it is based to a condition of unstable equi- 

 librium. If glacial conditions were developed In 

 India, Australia, and South Africa by a 70° move- 

 ment of the crust, were the movements to and from 

 It$ assumed position In Permian times so rapid that 

 the glaciation of these widely separated areas appear 

 to be geologically contemporaneous? If such move- 

 ments had occurred, Instead of evidences of glacia- 

 tion over a wide area at the same period, we ought 

 rather to find that the glaciation in each of the wldely 

 separated points occurred during distinctly different 

 geological periods. 



But that Is not the only weak spot in the evidence. 

 The Permian (or Permo-Carboniferous) glaciation of 

 Australia took olace on the east and south-east of 

 the continent as" well as in Western Australia, and 



18 H. H. Hayden, Rec Geol. Surv. Ind., vol. vxxvi., p. 23, 1907. 



