270 Notes upon the Geology of the Bajmahal Hills. [No. 3. 



there are immense overflowing sheets of basaltic and other trappean 

 rocks, which have spread above the sandstones, and passed over 

 them in a molten state intensely altering the rocks, into contact with 

 which they have come, baking them into porcelanic and glassy masses, 

 and producing great and important changes in their aspect and 

 texture. 



These trappean rocks of varying character and composition com- 

 pose the surface rocks of nearly two-thirds of the whole area of the 

 Damin-i-koh : stretching continuously from south to north, forming 

 the highest ridges, as well as some of the lower valleys ; and im- 

 pressing on the district the peculiar character of its scenery and 

 aspect. In mineral composition, they vary from dense, close-grained, 

 almost compact, and vitreous basalt, to perfect pumice ; the greater 

 portion being of a dense and crystalline basaltic trap ; slightly vesi- 

 cular, occasionally abounding with olivine, and sometimes with glassy 

 felspar. 



In structure also, these rocks present every possible gradation 

 from the most perfectly prismatic and columnar forms, with inter- 

 locking joints, to the most homogeneous claystone, in which no 

 symmetry of structure can be perceived. In some of the more 

 massive varieties, the concentric spherical structure, so frequently 

 noticed in trappean rocks, is remarkably well seen. 



These old lava masses have been poured out at intervals, in many 

 successive flows ; and have, as might have been anticipated, been 

 irregular in their distribution over the surface ; although one fact, 

 which most forcibly strikes the observer is the remarkable persistency 

 in character, texture, and composition which prevails throughout 

 the entire area from north to south, over a district of some seventy 

 miles in length, and thirty miles in breadth. 



In all these traps, there is a comparative absence of that great 

 group of minerals, the zeolites, which in other large districts of the 

 same character are so common and abundant. Of this group natrolite 

 occurs in minute acicular crystals not uncommonly, but I have never 

 seen it of any great beauty. Stilbite and Heulandite are also found 

 (Karodih, Amrapara, &c.) ; and in some of the floors abundance of the 

 chlorophaite of Macculloch. But the minerals, which in the majority 

 of cases occur filling or lining the vesicles of the amygdaloidal varie- 



