136 The I'Jjfcct of Climate on Soil Formation 



however it is found to pass iibruptiy into very various formations, 

 trap, metamorpliic, sedimentary. In fact the association is remarkably 

 alike in the two cases. 



Some years ago Holland' drew attention to the fact that laterite is 

 largely not a silicate but a hydroxide of aluminium, and pointed to the 

 difficulty of explaining its formation on chemical grounds and suggested 

 that this might be attributed to organic life with greater prol)rtl)ility. 

 This suggestion has not 1 think been followed up. 



In a recent Memoir Harrison and llamaswamy Sivan- have detailed 

 the characteristics of the material which is largely res])()nsible for the 

 black colour of Ilegur, and have shown that it is a colloidal material 

 containing iron, aluminium and silica associated with a small pro- 

 portion of organic matter and is not attacked l)y concentrated 

 hydrochloric acid. The circumstances in the neighbourhood of a bed 

 of Regur are pecuUar, for at one place one can see the rock taking on 

 the dark colour of Regur, at another not far away the same rock is 

 weathering to red soil. It is quite possible that here too we have an 

 instance of bacterial action. 



In any case the formation of these two soils cannot be simply 

 attributed to either weather or climate. It occurred to me therefore 

 that the above facts might be of interest to those who are concerned 

 with the biology of soils. 



» Geolog. Mag. Vol. X. (1903), p. 59. 



° Memoir Dcpl. Agri. Intl., Chcin. Scr. Vol. Ii. No. 5. 



(Received August -lOt/i, litll.) 



