184- foote: south mahratta country. 



(8* to 10" in diameter), of gritty quartzite, occur enclosed in the trap. 

 The enclosed fragments show no trace of change on their surfaces ; but 

 the section is not a satisfactory one, both rocks being much weathered and 

 a good deal obscured by mud, brought over the surface by a small stream. 

 This was the only case observed of fragments of older rock enclosed in 

 one of the Deccan trap-flows. 



The decomposition of the trap rocks under certain circumstances 

 Decomposition of trap ^^^es rise to eminently clayey products containing 

 ^'^^®* a very variable, but often very large, percentage 



of iron ; under other circumstances the rock simply breaks up into soil 

 varying in character according to the nature of the parent rock. The 

 former kind of decomposition will be separately considered in a special 

 chapter further on, the results being features of striking import in the 

 geology of these rocks. The soils formed by the second kind of decom- 

 position will be described in Chapter X, which deals with superficial 

 deposits. 



The decomposition of many varieties of trap into ferrugino- 

 argillaceous materials may be seen taking place in endless sections, more 

 especially in the case of basaltic flows, in which the rock cleaves horizon- 

 tally into a quasi-bedding. Some very good instances of this are to be 

 seen near the top of the Amboli Ghat road. In columnar trap, however, 

 this degradation into a yellow crust, first of ochrey and then of lateritoid 

 character, is not at all or only very rarely seen ; this is most likely due 

 to the much greater rapidity with which percolating waters flow off 

 because of the numerous vertical joints, while they often lodge in the 

 horizontally-bedded traps for much longer periods. 



A very good section is to be seen on the flanks of the Nagurbetta,* 



about four miles north-north-west of Nalutwar, 

 Nagurbetta section. 



and there the trap formation seems to be made 



* The Canarese word " betta," forming the termmation of the name Nagurbettaj signi- 

 fies a hill or mountain, 



( 184 ) 



