INTRODUCTION. 7 



view to ascertain the probability of Gondwana coal measures being in 

 existence there. Mr. Oldham identified the boulder beds of Poka- 

 ran, already described by Mr. Blanford, and those at Bap, with the 

 Talchirs, and points out that as the sandstones underlying the Jurassic 

 limestones of Jaisalmir are probably of Mahadeva age, there is a 

 possibility of the coaUbearing Gondwana beds occurring in the inter- 

 vening area. The actual presence of these beds can only be ascer- 

 tained by boring, and Mr. Oldham recommends that borings should 

 be put down in the country west of Bap. Subsequently in 1887 

 Mr. Oldham revisited this ground and came to the conclusion that 

 the boulder beds of Bap were overlaid unconformably by sandstones, 

 probably of upper Gondwana age, and that any search for coal in 

 Jaisalmir would be purely speculative. 1 



In his other paper Mr. Oldham gives an account of the geology 

 of the country he passed through, with a sketch map and list of the 

 formations. 2 None of these are found in Marwar, though the lowest, 

 the Lathi group, containing plant remains and fragments of silicified 

 wood, was supposed by Mr. Blanford to correspond to the plant 

 bearing sandstones of Barmer. The group in which the " Ammonite 

 bed of Kuchri " of Mr. Blanford occurs is re-named the Abur 

 group by Mr. Oldham, since the stone is locally known by that 

 name. 



In the same volume of the Records Colonel McMahon published a 

 , g8 6. description of the microscopical characters of some 



Col. McMahon. specimens of Malani lavas, etc , collected by 

 Mr. Blanford at Barmer, and compared them with the felsites of 

 Tusham hill, on the northern border of Bikanir, described in a previous 

 paper. 3 This is the only information yet available on the petro- 

 graphy of these interesting lavas. 



1 Rec. Geol. Surv. Ind., Vol. XXI, Pt. I, p. 30. 

 » Ibid, Vol. XIX, Pt. 3, p. 157. 

 ' Ibid, Vol. XVII, Pt. 3, p. 101, 



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