264 VREDENBURG : SKETCH OF BALOcHISTAN DESERT. 



are undescribed, of Nummulites } Alveolina, Operculina. There are 

 some very large echinoids belonging to the genus Conoclypeus and 

 numerous specimens of Arachniopleurus semireticulatus> D. & S-> 

 a characteristic form of the Ranikct of Sind. 



The mountains of the Lar Koh consist principally of a still greater 

 thickness of the same limestone. It has sometimes a pseudo-conglom- 

 eratic appearance probably not unlike that described by several 

 observers in the limestone of the Bolin pass 1 and of other parts of 

 Baluchistan. Its apparent thickness is further increased by numerous 

 intrusive sills which follow the stratification so regularly that they 

 might be taken for interbedded lava-flows. Occasionally, however, 

 they are seen to cut obliquely across the strata and in many cases 

 their connection with vertical dykes is very clearly exhibited. 

 Moreover their penological characters are entirely different from 

 those of a lava. 



These intrusions which form such a conspicuous feature in the 



neighbourhood of Roba*t consist of hornblende- 

 intrusive rocks. 



syenites and augite-diontes. They occur either 



as bosses of a more or less elliptical shape, or else as dykes and 

 intrusive sills. The coarseness or otherwise of texture does not seem 

 to depend always upon the shape and size of the intrusions : the 

 diorites of Malik-i-Siah Koh and Robat Koh are generally fine- 

 grained notwithstanding the large dimensions of the bosses (Fig. 

 24), while in the Lar Koh sills of moderate dimension are much 

 coarser in texture. Some of the latter consist of an augite-diorite 

 which is remarkable for also containing olivine. In some places, the 

 large crystals of oligoclase exhibit a beautiful 



Oligoclase moonstone. . ... 



blue iridescence similar to that of some varie- 

 ties of moonstone. Like the Rds Koh syenite which it greatly 

 resembles, this rock also contains silicate of copper or chrysocolla. 

 The ore does not occur in distinct veins as at Drana Koh (page 74), 

 but like at the R£s Koh it is irregularly scattered through the rock as 

 one of its constituent minerals. In former times this ore seems to 



1 Mem. Geol. Surv. Ind„ Vol. XVI II, p. 30; XX, p. 112. 



