1854.] Notes upon the Geology of the Majmahal Hills. 271 



ties are agate and quartz. These occur in great beauty 'and variety, 

 of every size, from a mere point to some feet across ; forming a thin 

 coating on the surface of the vesicle, or partially or entirely filling 

 the cavity. In the majority of cases, these cavities have a thin coating 

 of natrolite immediately adjoining the trap, inside which the agates 

 have been formed. The quartz, when it occurs, is generally the in- 

 nermost or last deposited mineral. There has often been a repeti- 

 tion of these layers of agate, and quartz. In colour, they are generally 

 white, or smoke-coloured ; occasionally the agate layers have a red 

 tint, while the quartz crystals are sometimes, though rarely, of a beau- 

 tiful amethystine tint, (Burhait.) The agate occurs in botryoidal, 

 reniform, and mammillated groups, and some very beautiful speci- 

 mens have occurred. 



Connected with these trappean rocks is one of the most interest- 

 ing facts in the geological structure of the hills, bearing on the 

 question of the mode of their formation, and evidencing the long 

 continuance of the ancient volcanic forces which have produced these 

 immense flows of molten matter. 



The fact of these trappean rocks in all cases overlying, and altering 

 the sandstones, associated with the coal beds has already been stated. 

 But, resting upon these lower traps, and bearing all evidence of 

 having been quietly deposited upon them, occurs again another series 

 of beds of sands, and gravels, and of clays and muds, never attaining 

 any very great thickness. These again have been invaded by, and 

 covered by, another flow of trappean rock or lava, and above this 

 again, the same facts are repeated, beds of shales and sandstones 

 and clays occurring again and again, covered up by another sheet of 

 now-crystalline basalt. And this remarkable fact has been in one 

 or two cases distinctly repeated three or four times. In all these 

 instances, the lower beds of the mechanical rocks are unchanged, and 

 present their normal character of loosely aggregated sandstones, peb- 

 bly sandstones, or laminated clays ; in some cases consisting largely 

 of the disintegrated debris of the rocks on which they rest : while 

 with equal constancy the upper beds are in all cases greatly altered, 

 indurated and affected by the mass of lava-like rock which had been 

 poured out over them. The evidence is perfectly clear, that dur- 

 ing a very considerable period of time, forces, analogous to existing 



