PETR0GRAPH1CAL NOTES. gi 



above cited on the Boulder bed of the Salt Range. There seems to 

 be a singular dearth of accessory minerals in this granite ; even magne- 

 tite is rare. 



At the contact between the granite and rhyolite there is usually a 

 considerable development of hornblende in the latter. At times this 

 takes the form ot a growth of comparatively large nests of hornblende 

 which have apparently included portions of the groundmass. Along 

 the actual line of junction a row of small hornblende crystals pro- 

 jects into the granite, evidently formed before the mass of the latter 

 began to solidify (PI. XI, fig. 6). 



The Jalor granite differs from that just described mainly in con- 

 taining mica as the principal ferromagnesian constituent instead of 

 hornblende. There is also a fair proportion of plagioclase felspar as 

 well as orthoclase. The mica is of two kinds, muscovite and biotite 

 The former predominates in a specimen from Manpur near Pali, No. 

 i2'2f>$, while biotite alone occurs in the granite of Jalor hill, No. 

 11716. 



4. Basic Dykes. 



I am indebted to Mr. Holland for the following description of the 

 specimens collected from the dykes in the area surveyed. The ordi- 

 nary dykes traversing the rhyolites and granites, when unaltered, like 

 the rock composing the large dyke to the south of Jalor (No. 11715) 

 are olivine dolerites or diabases, and consist of " plagioclase felspar, a 

 " basic variety giving extinctions near labradorite (bytownite) ; olivine 

 " in isolated crystals and in clusters partially serpentinised, but with- 

 " out ' reaction borders ' at their junction with the plagioclase ; pale 

 " red brown augite, forming sub-ophitic intergrowths with the felspar 

 " and olivine ; apatite in numerous well shaped prisms ; opaque black 

 " iron ores in large lumps with crystalline shapes, and a small quantity 

 " of brown biotite often associated with the iron ores." The rock is 

 medium or coarse grained in the centre of the dykes, but near their 



( 91 ) 



