128 NOTE. 



of sandstone wKicli is covered by some thick-bedded limestone with mach segregated 

 silica, above which comes some thin-bedded, clear, quart^ose, fine-grained sandstone. 

 The breccia at the bottom of the section is remarkably like some varieties met with 

 in the slate series, and hence it was considered to be an inlier of that formation. It 

 seems, however, that it should be referred to the ferruginous beds, mentioned at 

 page 31 as occurring under the limestone No. 2, and is hence a strictly lower- Vindhyau 

 rock. 



The origin of the ' trappoid beds' (page 34), is very obscure, but the observations 

 of last season tend to support the conclusion that they are not of truly igneous origin 

 (that they have not originated from a state of fusion). Some parts of the trappoids, as 

 about Hoorkahoorkee, do bear a most remarkable resemblance to igneous rock, and 

 may really be so, but in most places the rock has a more sedimentary appearance and 

 thin bands of it are found (as north of Kujrahut, &c.,) interstratified with the por- 

 cellanic beds, and made up in part of angular fragments of rock similar to the por- 

 cellanics themselves. These vary in size from a pin's head to half an inch, or some-- 

 times much more, and are imbedded in a felspathic sandy matrix. It is not improbable 

 that the smaller at least of such fragments would have been fused and incorporated 

 into the matrix of the rock if the latter were igneous, for the edges of fine splinters 

 of such are rounded in the fiame of a blowpipe. The well marked bedding which 

 some portions of the trappoids exhibit, as well as the thin bands not exceeding a yard 

 in thickness sometimes seen interstratified with the porcellanics, and the absence of 

 vesicularity, furnish additional evidence against their being an igneous (fused) rock. 

 Some varieties occur apparently intermediate in character between the trappoid and 

 the porcellanic beds, and it seems probable that both have been formed from a somewhat 

 similar debris, the porcellanics from an impalpably fine mud, and the trappoids* from 

 less finely comminuted materials. Analyses of two specimens by Mr. Tween, support 

 this conclusion, as they indicate a very similar composition. 







Porcellanic 



Trappoid 







rock. 



rock. 



Soluble in acid ... ... 





5-5 



4-8 



Insoluble 





94-5 

 100-0 



95-2 





100-0 



Silica 





86-81 



79-35 



Alumina ... 





6-25 



12-23 



Sesquioxide of Iron. Present also as protoxide 



with 







a trace of sulphide 





3-1 



2-5 



Lime 





0-12 



0-14 



Magnesia ... ... ... ... •, 





trace 



trace. 



Potash 





4-1 



4-5 



Soda 





1-0 



lOl-SSt 



31 





101-82 



* Those at least having a sedimentary appearance. It is perhaps doubtful whether the highly igneous 

 looking rock of Hoorkahoorkee may not have a different origin, 

 t Contains also traces of arsenic and copper. 



( 128 . ) 



