Address hy Prof. Sir T. H. Holland. 417 



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. Professor E. Koken, of Tiibingen,^ 

 in an elaborate memoir entitled Indisches Perm und die Pcrmische 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 

 publication 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 suggested 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 

 re arrangement of the great inequalities on the Earth's surface would be 

 insufficient to produce any appreciable sliding of the order required 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 1886 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 equatorial region even to the 

 Polar circles. Oldham drew 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 changes as great as the transfer of 

 lands from the Polar circle to the Tropics has the objection that characterizes 

 a surveyor's use of ' unfavourable ' triangles in a trigonometrical survey. Before 

 admitting, therefore, that these small changes of latitude and of azimuth may 

 be classed with the palseo-glacialists' evidence as data of the same kind, though 

 so utterly different in magnitude, it is desirable briefly to examine the geological 

 evidence regarding past ice ages in extra-polar areas. 



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 3-5° 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 

 of31"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. 



^ N. Jahrb. filr Min. u.s.w., p. 537, 1907. 



- J. Evans, "On a possible Geological Cause of Changes in the Position of 

 the Axis of the Earth's Crust " : Proc. Hoy. Soc, vol. xv, p. 46, 1866. 



•'* J. Evans, Presidential Address, Proc. Geol. Soc, 1876, p. 105. 



•* J. F. Twisden, " On possible Displacements of the Earth's Axis of figure 

 produced by Elevations and Depressions of her Surface " : Quart. Journ. Geol. 

 Soc, vol. xxxiv, p. 35, 1877. E. Hill, "On the possibility of Changes in the 

 Earth's Axis": Geol. Mag., 1878, pp. 262, 479. O. Fisher, "On the 

 possibility of Changes in the l^atitude of Places on the Earth's Surface": 

 Gkol. Mag., 1878, pp. 291, 551. 



^ Geol. Mag., 1886, p. 304. 



DECADE YI. — VOL. I. — NO. IX. 27 



