246 VREDENBURG: SKETCH OF BALUCHISTAN DESERT. 



as at Chagai, but in much larger outcrops where the structure becomes 

 granitic as in the present instance at Pushtiwan or in the still more 

 granitic looking rocks of Malik Naro to be mentioned hereafter. It is 

 true that large as they are these outcrops are small compared with the 

 enormous mass of R£s Koh and that this might account for their less 

 perfectly granitic structure. The Ra"s Koh rocks do not contain any 

 quartz, therefore they cannot show any micropegmatite. But at Bibi 

 Mah in Persia there is an intrusion comparable in size to the R3s Koh 

 mass and similar to it in age and in its mode of occurrence, and differ* 

 ing in composition, as it is like the rocks at present under considera- 

 tion a quartz-diorite very rich in silica. The main mass of the intru- 

 sion has a granitic structure; but near its junction with the tertiary 

 sediments and in the narrow dykes that surround the main mass the 

 structure becomes porphyritic, with however only a slight tendency 

 to the formation of micropegmatite. At Bibi Mah as at Ra"s Koh 

 the intrusive rocks are acid and intermediate. But in the case at 

 present under consideration there are also large basic intrusions, and 

 it has been noticed by several observers that some connection seems 

 to exist between basic intrusions and micropegmatite. !f, however, 

 that connection does exist in the present case, the acid rocks must 

 belong to the age of the flysch to which the basic intrusions most 

 probably belong, and they must be older therefore than the igneous 

 masses, upper eocene at the earliest, that form Ra"s Koh and Bibi 

 Mah. 



The great basic intrusions of Cha*gai, Pushtiwan, etc., I have thus 

 regarded as the deep-seated portions of a volcanic centre of the flysch 

 period. The products ejected from volcanoes of that system are 

 often basic; but acid eruptions were also abundant. Thus the acid 

 intrusions associated with the basic ones might themselves be con- 

 nected with volcanic activity: the deep-seated portions of the acid 

 eruptions must exist somewhere making it perfectly intelligible that 

 plutonic acid rocks may exist both of the age of the flysch and also 

 of later tertiary age. But the survey of all this region has not 

 advanced far enough as yet to solve these problems, 

 f 68 ) 



