Records of the Geol.oiji.cul Survey if India. 
[VOL. V. 
yo 
Lithologically the trap rocks consist principally of various kinds of dolerite, rich in 
augite, the prevailing forms being compact basalt, anamesite, and more or less earthy amyg¬ 
daloid. Two of the most characteristic rocks are a porphyritic basalt containing tabular 
crystals of glassy' felspar, and an amygdaloidal earthy trap abounding in small nodules of 
agate and zeolite surrounded by green-earth; the latter of these is exceedingiy abundant. 
Some of the amygdaloids contain great quantities of zeolites and allied minerals; of these 
the most abundant are Apop/iyllite, Stilbite, Heulandite, Scolecite, and Laumonite. 
Besides these Chalasite, Hypostillite, and Thomsonite occur, but they are rare, and I have 
once seen Prehnite. The ApopliylUte is finer than at any other known locality, and of 
various colours, white, green, and pink. A great variety of agates and of other forms of 
silica, such as bloodstone, are also met with filling cavities or forming small veins in the 
rock. 
The traps of the trachytic group in which felspar predominates, and which may he 
recognised by their pale color, are much less common, and are in fact only met with in a 
few localities, as at Dliaravi in Bombay Island, Powagarh hill, east of Baroda, &c. They are 
usually ashy or earthy, but sometimes crystalline. 
The whole series of Deccan traps is regularly stratified in beds, or, to speak more correctly, 
flows, varying from 5 or 6 feet to npwards of 200 in thickness. The average in two roughly 
measured sections on the railway-inclines of the Tol (Thull) and Bhor ghats is apparently 
87 and G4 feat respectively, hut really’ less, because the distinction between any two beds 
can, in general, only be made out by mineral characters, and if, as frequently happens, two 
successive strata present no lithological differences, they are liable to bo classed together as 
one. Many apparently massive strata of amygdaloid really consist of a number of separate 
flows from 6 to 10 feet thick, and it is doubtful if the average thickness of the strata exceed 
20 to 30 feet. 
A remarkable horizontality prevails throughout the greater portion of the trap area, the 
most important exceptions being in the Rajpipla hills, and the ranges immediately north of the 
Narbada, in parts of the Satpura hills north of Kkaudesh, and along the coast from some 
distance south of Bombay' to Daman. In these exceptional areas the dips are clearly duo 
to disturbance subsequent in date to the consolidation of the rocks, for sedimentary beds, 
which must originally have been horizontal, have shared in the movement. It is thus clear 
that throughout the area the traps must have originally been very nearly level. 
Yet there can bo no question but that these rocks are of volcanic origin. In many 
places beds of breccia are interstratified, which must originally have consisted of volcanic ash. 
Some arc met with on the northern part of the Bombay Island, at Sion hill, Palshachi hill, 
Flagstaff, and Itai hills, and more in Salsetto, the caves of Kanban being excavated in one of 
them. Several beds are cut through on the Karaatkd ghat on the road from Piinah to 
Mahableshwar, and a very conspicuous instance may bo seen at the lower gateway of the 
bill fort of Singurh near Piinah. Indeed with a little search similar beds may be found 
almost anywhere in the trap country’. When weathered, the resemblance of these breccias, 
with their enclosed scoriaceous blocks, to the ash beds of old volcanic cones is so exact that 
no doubt can remain as to their being of identical origin. The red bole which so frequently 
occurs interstratified with the traps may also be an ash, as it is intermixed with scoria) in 
places, but it sometimes hears the appearance of having been rearranged by water. It 
should not be forgotten that the blocks which were originally vesicular or scoriaceous are now 
amygdaloidal, the hollows in them having been filled by infiltration. 
But whilst the volcanic origin of the Deccan traps is unquestionable, their horizontality 
and regularity of stratification render them very unlike the accumulations of volcanic rocks 
now forming in countries in which igneous vents exist, and it is clear that the circumstances 
under which the former were accumulated were widely different from anything now known to 
