290 VREDENBURG : SKETCH OF BALOCHISTAN DESERT. 



large masses, and in smaller dykes, they exhibit porphyritic charac- 

 ters. Some of the quartzless rocks are somewhat basic, though 

 they never become typical gabbros and dolerites, at least not in any 

 rocks which can be without any doubt attributed to this group. 



Amongst the rocks with reference to which some doubt arises 

 as to their proper attribution to group 1 or group 2, are some very 

 interesting diorites and diorite porphyries that contain a large 

 proportion of micrographic quartz. Some of them have been in- 

 truded amongst gabbros, and it would be interesting to study more 

 closely the field-relations of the two rocks as the association of 

 granophyre and basic rocks has already been noticed in other locali- 

 ties. 



The rocks which have been referred to group 4a and which per- 

 haps represent a period of volcanic activity of Siwalik age, are both 

 intrusive and effusive. They are either intermediate or basic and 

 are remarkable for the extreme freshness of their minerals. Some 

 of them belong to somewhat exceptional types, for instance, a diorite 

 porphyry apparently containing a felspathoid, in the desert near 

 K6h-i-Dalil, and a very beautiful limburgite which occurs as a dyke 

 at Robdt. 



Lastly, the recent volcanic products that constitute group 4b 

 are remarkably uniform in character as has been noticed in the 

 chapter dealing with that formation. A great many contain a horn- 

 blende that exhibits some exceptional features. 



The study of this vast collection is not yet sufficiently advanced 

 to allow of any generalisations being formulated. The distribution 

 of the minerals presents some noticeable peculiarities. In all the 

 groups above mentioned, augite is a very plentiful mineral either to 

 the complete exclusion of hornblende, or frequently associated with 

 it. Sometimes this may be due to the transformation of augite into 

 uralite, while the reverse change of hornblende into pyroxene is also 

 seen in a great many rocks of group 4b, But in most cases, in 

 which the pyroxene and amphibole are associated, they both occur 

 as primary constituents of the rock. 

 ( 112 ) 



