THE 



GEO LOGICAL MAGAZINE 



NEW SERIES. DECADE VI. VOL. V. 

 No. IX.— SEPTEMBER, 1918. 



I. — The Physiographic Significanck of Laterite in Western 



Australia. 



By W. G. WOOLNOUGH, D.Sc, F.G.S., Professor of Geology, University of 

 Western Australia. 



DURING the last six or seven years a series of valuable papers 

 bearing on the origin of laterite has appe;ired in tlie Geological 

 Magazine.^ The conclusions arrived at have been somevi^hat diverse 

 and contradictory. Dr. Termor, on the one hand, regarded the 

 laterites of India as residual in character, and believed that the}' 

 represented the insoluble residues left in the process of rock 

 ■weathering after the soluble constituents had heen removed in 

 solution. Mr. Simpson, at the other extreme, suggested that they 

 represented the soluble material, leached out of the subjacent rocks 

 during weathering under peculiar conditions, and deposited as a 

 chemically-formed rock by precipitation at the surface of the earth. 



Mr. Holmes and Professor Lacroix both appear to hold much the 

 same view as that enunciated by Mr. Simpson. The fact that 

 Dr. Fermor, in his admirable revievs^ of the work of Lacroix, does 

 not dissent from the statements of the latter, suggests that Dr. Permor 

 and Mr. Simpson may really hold very similar views, and that the 

 apparent differences may he, after all, due to method of expression 

 and not to actual divergence of opinion. 



It is quite possible that different methods of formation may occur 

 under the widely different conditions of climate and geology exhibited 

 by the various regions from which laterite has been described. 

 Whether this is so or not, the author is wholly in agreement witli 

 Mr. Simpson in his explanation of the chemistry of laterite formation 

 in Western Australia, but desires to go further and to extend and 

 amplify the physiographic processes involved in the genesis of this 

 peculiar rock. 



A very brief summary of the physiography and geology of tlie 

 south-western portion of "Western Australia^ will assist in the 

 understanding of the problem. The most important feature of all is 

 the Darling Range Escarpment. This extends as a straight line for 

 at least 200 miles in a north and south direction from near Gingin 



^Notably L. L. Fermor, "What is Laterite?": Geol. Mag., 1911, 

 pp. 507-16, 559-66 ; E. S. Simpson, " Laterite in Western Austraha " : ibid., 

 1912, pp. 399-406 ; A. Holmes, " The Laterite Deposits of Mozambique " : 

 ibid., 1914, p. 529 ; L. L. Fermor, " The Laterites of French Guinea " : ibid., 

 1915, pp. 28-37, 77-82, 123-9. 



" For a more detailed account see J. T. .Jutson, Bull. No. 61, Geol. Surv., 

 Western Australia. 



DECADE Yl. — VOL. V. — NO. IX. 25 



