DETAILED DESCRIPTIONS OF ROCKS. 75 



fossils anywhere in these sandstones, but they resemble the sandstones 

 of Barmer so closely that there is little doubt that they belong to the 

 same group. The sandstone of the two outliers to the south, near the 

 villages of Sanpa and Sarnu, is precisely similar. They all dip at low 

 angles, from 7 to io degrees, in an easterly direction. On the east 

 side of the Sarnu outlier there is a large boss composed of a dark 

 grey basic rock containing a^gerine-augite, sanidine and sodalite with 

 perhaps nosean, resembling a tinguaite from the neighbourhood of 

 Montreal, 1 and is thus quite different from the material of which 

 the ordinary basic dykes traversing the rhyolites are composed. 

 From its position it appears to be intrusive in the sandstones, but 

 the actual junction between the two rocks is concealed by sand. 



Thirteen miles to the north of Nausar, near the village of Khatu, 

 there is a chain of small hills running from south-west to north-east 

 for a distance of about seven miles. These are all composed of 

 rhyolites, a reddish brown highly porphyritic variety with numerous 

 crystals of pink felspar. 



To the west of the outliers near Nausar the country for a distance 

 of about 25 miles is entirely covered with sandhills, among which 

 there are no outcrops of solid rock. Beyond this again, to the west 

 of Barmer, there is a larger area, extending from Bonthia in the 

 no.-th to Chotan in the south, a distance of 40 miles, and from Barmer 

 westwards to the edge of the map, a distance of about 27 miles, in which 

 numerous rock islets are scattered about protruding from the undu- 

 lating surface of the sand in a manner which suggests the summits 

 of a large mountainous island partly submerged beneath the sea. By 

 far the greater portion of these hills are composed of the Malani 

 rhyolites, and these do not present so great a variety as those occurring 

 on the eastern side of the desert about Jodhpur and Siwana, but con. 

 sist for the most part of compact dark grey, sometimes black, glassy 

 or pitchstone like lavas containing porphyritic crystals of white or 



1 Rosenbusch. Mikr. Phys. Mass. Gest., 1896, p. 483. 



( 75 ) 



