177 



ON SOME SUPERFICIAL DEPOSITS IN CUTCH. 

 By the Rev. J. F. Blake, M.A., F.G.S. 



[Abridged/ ] 

 Part I, 

 (WitJk a Plate.) 

 During a recent visit to Cutch for the purpose of studying the Jurassic ^ 

 rocks there exposed, my attention was naturally attracted to a number of 

 superticial deposits, which in some cases concealed, and in others were asso- 

 ciated with, the solid rocks beneath, I cannot pretend to have made an 

 exhaustive study of them, as I have only examined such parts as may be 

 found in the Jurassic area ; but these have suggested certain theories of 

 their origin which I have not seen proposed elsewhere ; and as these theories 

 depend on observations which I do not find recorded, it may at least be 

 hoped that an account of such observations may throw light on the origin 

 of the deposits. The matters with which I propose to deal may be classed 

 under the following heads : — 



(1) Subrecent concrete. 



(2) The boulder-beds associated with this concrete, 



(3) Infratrappean grits. 



(4) Laterite. 



(5) Alluvium and Ran. 



Of all these, except No. 2, there are to be found brief descriptions in 

 Mr. A. B. Wynne's memoir on the geology of Cutch = ; but, as a rule, that author 

 does not venture on any suggestion as to their origin, and in no case does he 

 appeal to the particular causes to which I have been led to refer them. 

 (1) THE SUBRECENT CONCRETE. 



Under this name Mr. "Wynne describes some remarkable deposits, of which 

 he writes as follows : — " Very generally distributed over the hilly country is 

 the subrecent calcareous deposit already alluded to. The white sandstones 

 of which it consists are sometimes sufficiently coherent to be used for build- 

 ing, and it is very commonly burnt for lime all over the province. No 

 fossils have ever been found in it, but on some slabs from the deposit in 

 Western Cutch tracks of Crustacea or of annelids have been observed. It is 

 not limited to a uniform level in its various situations, having been met with 

 in the low ground at the foot of the hills bordering the Runn as well as 

 high in their glens. Its aspect is always very much the same, though its 

 texture is varied, being sometimes conglomeratic or finely oolitic, and 

 generally it presents some oblique lamination."^ 



1 [By the omission of that portion of the paper in which the quartzite-reefs and their 

 mode of formation were discussed.] 



- Throughout this memoir I use the word " Jurassic " for all the rocks so coloured on 

 Mr. Wynne's map without prejudging the question as to how many of themj may be, as 

 Bome certainly are, of Neocomian age. 



^ Mem. Geol. Surv. India, vol, ix,pt. i (1872), 4 Jliij,p,8l, 



23 



