Dr. Hugh Warth — Dolerite and Laterite Compared. 21 



IV. — Weathered Dolerite op Eowley Eegis (South Stafford- 

 shire) COMPARED WITH THE LaTERITE OF THE WESTERN GhATS 



NEAR Bombay. 



By Dr. Hugh Warth. 



SINCE it has been proved that large areas of basaltic and other 

 igneous rocks within or near the Tropics in India, on the 

 Seychelles, and in Australia yield surface deposits (so-called Laterites) 

 identical with Bauxite, it is of great importance to ascertain exactly 

 what products of decomposition or weathering originate from 

 corresponding rocks in a temperate climate. 



My attention was drawn by Professor W. W. Watts to beds of 

 weathered rock which overlie the Dolerite of Eowley Eegis. These 

 beds are about 20 feet in thickness and ochre-coloured. The material 

 is so soft that it is easily crushed between the fingers, whilst its 

 mineralogical composition and its mode of occurrence leave no doubt 

 as to its having been formed in situ from the Dolerite. I therefore 

 decided to analyse this product. The following table contains the 

 result : — 



Column i of the table represents the composition of the original 

 Eowley Eegis rock, which was obtained as the average of three 

 analyses, two of them by J. H. Waller ^ and a third analysis by 

 Henry. 



Column ii, the weathered product of Eowley Eegis (steam dry). 



Column iii/composition of Dolerite from Poonah on the Western 

 Ghats in the Bombay Presidency (analysed by my son F. J. Warth, 

 M.Sc). 



Column iv, the composition of the Laterite which rests on the 

 Dolerite at Mahabaleshwar, which is also situated on the Western 

 Ghats (see p. 155, Dec. IV, Vol. X, of this Magazine, April, 1903, 

 by H. &F. J, Warth). 



Total 



100-4 



99-3 



100-5 



100-0 



This table shows the striking difference between the weathering 

 of the Eowley Eegis Dolerite and that of the Dolerite of Poonah, 

 which so far may represent the whole of the Deccan Trap. Whilst 



1 For one of these two analyses see Teale's Petrology ; the other being unpublished, 

 Mr. Waller kindly permitted me to make use of it. 



