22 Dr. Hugh Warth — Dolerite and Laterite Compared. 



the Rowley Regis Dolerite yields a product (column ii) wliicli differs 

 comparatively little from the original rock, this Dolerite of the 

 Western Ghats is altogether changed into a mixture of aluminium 

 hydrate and ferric oxide, the most remarkable fact being the nearly 

 perfect removal of the silica in the latter case. 



For a further test I levigated a sample of the Rowley Regis 

 product very carefully by suspension in water, and I obtained about 

 10 per cent, of the whole as a very fine ochre-coloured powder. The 

 composition of this fine powder steam-dried was as follows : — 



Si 0, 48-3 



TiO's -5 



PaOg -8 



Al, O3 22-9 



Fe2 O3 11-6 



FeO tr. 



Mg 1-4 



Ca 3-8 



K2 ... 2-4 



Nag 1-6 



H2O 6-8 



100-1 



There is no essential difference between this fine matter and 

 the entire weathered jjroduct, column ii of the table. Comparing 

 the weathered product with the fresh Rowley Regis rock, we find 

 that the process of weathering has resulted in the removal of far 

 more basic substance than of silica. There is no tendency towards 

 the formation of a Bauxite, but rather towards that of a clay. The 

 relation is the same as indicated in a few other cases by Merrill, 

 pp. 215, 216, and 223 of his work on Rock- weathering. Merrill 

 was able to illustrate even a complete change into clay in one or 

 two instances, and we may safely conclude that the ultimate product 

 of the Rowley Regis rock would also be a complete clay. Anyhow, 

 this Rowley Regis product represents altogether a different trans- 

 formation from that which took place in India. 



No chemical reaction is known which can account for such 

 a complete removal of silica as has occurred in India, neither is 

 there any explanation why such a reaction should work in India 

 and not in England. The only hypothesis we have is the one 

 based on Mr. T. H. Holland's novel and ingenious suggestion ^ that 

 the silica might be rendered soluble by lowly organisms which can 

 thrive in the uniformly warm climate of the Tropics, and not in 

 a region of lower and varying temperature. However, there is as 

 yet no actual proof for this hypothesis, and under the circumstances 

 it may not be inappropriate once again to draw the attention of 

 chemists to tliis remarkable phenomenon in case there might after 

 all be a strictly chemical solution of the problem. 



There is one jjoint which requires still to be mentioned. In the 

 above it was assumed that the surface deposits of Laterite (or Bauxite) 



' T. H. Holland on the Constitution of Laterite, Geological Magazine, Dec. IV, 

 Vol. X, February, 1903, pp. 69-69. 



