3TRATIGRAPHICAL FEATURES. 31 



nothing of the kind. For the present, therefore, the origin of these 

 mysterious markings must remain undecided. 



7. Boulder beds of Bap and Pokaran (Talchir). 



The next group of beds in succession to the Vindhyans has already 

 been alluded to several times ; these are the boulder beds exposed at 

 Bap, Pokaran and other places on the eastern borders of Jaisalmir. 

 I have not met with these beds in any part of the area surveyed by 

 myself, but they are described by Mr. Blanford as consisting of 

 " green, red and variously coloured shales, occasionally soft, but often 

 hard and even porcellanic. Some are fine, others are coarse and 

 sandy, and contain grains of pink felspar, and of a green mineral 

 resembling epidote ; some beds being composed throughout of one 

 or the other of these minerals. Jn places, pebbles and boulders of 

 the Malani porphyries and syenite are found towards the base of 

 these shales ; the boulders being occasionally from three to four feet 

 in diameter, whilst remains of much larger blocks, which had fallen 

 to pieces, but which could not have measured less originally than 

 twelve to fifteen feet in diameter, were seen about Lowo. These 

 boulders appear to have been brought from a distance, and there is 

 some reason for supposing that they may have been transported by 

 ice, as the underlying surface of the Malani porphyries near Pokaran 

 was in one instance found to be grooved and striated." 1 



These beds were supposed by Mr. Blanford to underlie the 

 Vindhyan sandstones, and Mr. Oldham was at first of the same 

 opinion, but 40 miles to the north-east of Pokaran, near the village of 

 Bap, exactly similar beds are seen, but containing, in addition to 

 boulders of the Malani lavas, pebbles derived from the Vindhyan 

 limestone, which must therefore have been indurated and metamor- 

 phosed before the accumulation of the boulder beds. 2 The difficulty 



1 Rec. Geol. Surv. Ind., Vol. X, Pt. I, p. 17. 

 = Rec. Geol. Surv. Ind., Vol. XIX, Pt. 2, p. 123. 



{ 3 * ) 



