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Records of the Geological Survey of India. 
[VOL. V. 
of course, the confirmation of their close affinity would be a link in the chain of evidence 
he brought to bear upon the age of the eruptive rocks. Thus the solution of this interest¬ 
ing question seems closely connected with the determination of the correspondence of 
the thigh beds and those similar deposits on the same infra-trappean horizon. 
The Lametas, though so much more extensively developed than the intertrappeans 
have yielded comparatively few fossils. Vertebrate remains, some very large, have been found 
in them at Jabalpur, and elsewhere some shells, establishing the fresh water origin of the 
group ; and so far, its prim/t facie connection with the intertrappeans. One would 
then naturally go on to apply the same explanation to the formation of this fresh water 
basin as that given by Mr. Blanford for the intertrappeans, namely, the stoppage of local 
drainage by the outflow of trap. This would at once annex the Lametas to the trappean 
formation. The great comparative continuity and extent of the Lameta deposits 
presents some difficulty to this supposition; the conditions would rather suggest some 
more general cause, such as tilting of the surface, by which the drainage of a large area 
would bo thrown back, and the direct evidence which might be looked for to connect them 
with the trap is wanting. There is not a single instance known throughout this extensive 
formation of a bed passing from it over and between trap flows, although it is very common to 
find trap close to thick Lameta deposits, and at a lower level. This circumstance involves 
considerations, some of which have an important bearing upon tho relations of the two 
formations, implying, as it does, either (1) abrupt inequality in the Lameta deposits; 
or (2) considerable pre-trappean denudation ; or (3) disturbance of the deposits, whether 
before or after the advent of the trap. The principal object of the present paper is to 
illustrate this feature of the case. 
The Lameta group is well exposed in the immediate neighbourhood of Jabalpur. 
The undulating ground to the east of the station is on the thick soft sandstones and 
pale shaly clays of the Jabalpur group; the flat hills beyond being of the Lamdta 
beds, capped by trap. On the little ridge to the north-east of the station, the Lametas show 
their greatest development, being about 150 feet thick. The south-west summit of this 
ridge, locally called Chota Simla, is capped by about 20 feet of trap; and on the 
north-east, where the Trigonometrical Survey Observatory Station is erected, there is a 
crest three-quarters of a mile long formed of trap, to a thickness of about 50 feet. 
This ridge quite overlooks the trappean plateau to the south-east, from which it is partly 
separated, on the west, by the valley of the Marjadlia stream, cut through the Jabalpur 
sandstone, the base of the Lametas here being close nnder the stoop rise of the ridge. 
This level is maintained by the junction along the little valley, at the head of which the trap 
of the plateau rests upon the Jabalpur group, thus giving a strong case of apparent 
unconformity, the whole 150 foot of Lametas disappearing within a distance of half 
a mile, at the level of the bottom bed. South of the little valley the Lametas come in 
again at first only 5 to 10 feet thick, but increasing gradually to tho south, the base 
of the group sloping down under the alluvium in a length of about one mile and a half. 
Regarding the junction of the Lameta group with the Jabalpur beds this section 
gives apparent presumption of unconformity. It would bo difficult to give clear evidence • 
on this point from this locality, on account of the massive irregular structure of the 
Jabalpur deposits ; and it is evident that such features as those described might be caused 
by a slight undulating disturbance of two conformable groups, followed by denudation 
before tho advent of the trap. There is, however, ample evidence elsewhere of the dis¬ 
cordance of the Jabalpiir and Lameta groups; the latter passing indiscriminately across 
the former, and even here, at the east base of the observatory hill, an inlier of Jabalpur 
sandstone is weathered out from the surrounding Lameta limestone. 
