PART 4.] 
Medlicoll: Lameta Formation. 
117 
But it is the upper junction that we are now concerned with. For this case the sup¬ 
position of slight disturbance and considerable denudation of the Lametas, both pre-trappean, 
is prima facie suggested by the section described. It is desirable, though difficult, to keep 
separate the argument for those two operations. If the supposition of disturbance ho 
excluded, thereby leaving the present under-surface of the LamStas the same as at the time 
of deposition, it becomes almost necessary to suppose that they extended in greater force 
than we now find them over the ground to the south, and hence that they were removed 
before the overflow of the trap; for, it is difficult to imagine how, in a small area, the 
thickest deposits could be accumulated on the highest ground, much of them being composed 
of fine sand and clay. It is not either a uniform thinning to the south ; for in that direction 
they thicken again before passing under the alluvium. If we are to explain the great con¬ 
trast in thickness to the north and the south of the little valley by the presence, at the 
time of deposition, of a ridge of Jabalpur sandstone in the position of the present valley, 
the fact of pre-trappean denudation would be equally established, for the trap now rests 
on the sandstone, at the head of that valley, at the level of the bottom beds of the LamCtas. 
If, on the other hand, we explain the fact of the deposits being at present thickest on 
the higher ground, by supposing a change of level subsequent to deposition, it would be 
possible to dispense with denudation, and we should be called upon to decide whether the 
disturbance occurred before or after the out-pouring of the trap. The very rough structure 
of stratification in volcanic rocks would make it very difficult, indeed, to find conclusive 
evidence for or against this position. It can only be said that tlio general distribution of 
the Lameta deposits suggests a slight relative change of level since their formation; and 
that the only direct observation bearing upon this point seems to show that the trap did 
not participate in that movement: at the base of the low scarp east by south of the village 
of Pachperi there is a marked apparent dip of the Lameta limestone by which the trap 
does not seem to he affected; on the contrary, the level is maintained by a thickening of the 
sand overlying the limestone. This dip is spoken of as ‘ apparent,’ because the original 
irregularities in the Lametas are so rapid that one cannot be certain that the feature here 
was really induced by disturbance. 
The internal evidence of the Lameta deposits throws some light upon these general 
considerations. No constant sequence or composition could be given for the group. A 
limestone is its only general characteristic; sometimes forming the whole of the band, 
sometimes quite subordinate in detrital deposits. All these conditions are illustrated at 
Jabalpfir. At the point of Chota Simla hill, and on the outlier to the west of it, the 
section is as follows:—at base is a thick, false-bedded, fine, porous, friable sandstone, pale, 
generally of a green tinge, sometimes a deep glauconite green (but not from green grains), 
locally purplish and mottled. At top it is much mixed with fine laminated clay, which 
again passes into earthy, dirty, pebbly, sandy limestone. It is in this bed and locality that 
vertebrate remains have been found. This limestone is here overlaid by fine crumbling 
sandy clay, pale purple mottled by green. Sandy layers are frequent, also strings of 
nodular limestone. The top limestone is a development of this tendency: it is prominently 
sandy, and is overlaid by sand. The crest of the ridge between the two terminal cappings 
of trap is formed of this upper limestone. To east of Chota Simla the lower limestones 
thicken greatly, replacing the bottom sand; and the whole section varies indefinitely. Under 
the trap on the observatory hill the top sand is well developed; a peculiar rusty, soft, fine¬ 
grained rock, quite devoid of earthy matrix; very like a common form of decomposing 
Jabalpur sandstone, but quite unlike the usual sands of the Lameta group. This peculiarity 
makes it very useful in revealing the internal arrangement of the group, as it happens to be 
pretty generally distributed in this neighbourhood. Thus, on the south side ot the little 
valley of the Marjadlia (see the figured section) there is a scarped terrace formed of a single 
