170 Becordx of the Geological. Surveij of India. [voi,. XT. 
and Feden snhcorneus. The boundary between the two groups is consequently, to 
some extent, arbitrary. 
On the other hand, Mr. Fedden has observed at one spot on the west side 
of the Laki range, a few miles from the northern extremity of the range near 
Sehwan, distinct unconformity between the upper and lower Nari groups, the 
sandstones forming the higher portion of the gi’oup resting upon the denuded 
edge.s of the brown lime.stones composing the lower sub-division. This is an 
excellent example of the manner in which the sub-divisions of the tertiary series 
change, the groups of one locality passing into each other, and new breaks oc¬ 
curring. It should be remembered that the Hari beds are entirely wanting east 
of the Laki range, and Manchhars, with, in places, a thin representative of the 
Gaj beds at their base, i*est nnconformably on Khirthars. 
Gdj groiq }.—There is but little to add to the general description of this 
group also. A measured section of the beds on the Gaj river, where they are 
especially exposed, show.s that the whole thickness of the group is but little less 
than 1,500 feet at that spot. To the northward the thickness of the Gaj beds 
must be less, and it is probably smaller in lower Sind also. On the Gaj the 
greater part of the whole thickness consists of sandy shales and clays, with 
gypsum, the hard limestone beds, though far more conspicuous, being only 
subordinate. In the Habb valley however, where the Gaj beds form exten¬ 
sive plateaus, surrounded by scarps in which the rocks of the group are well 
exposed, the mass of the Gaj strata ap 2 >ears to consist of limestone, and the 
boundary between them and the Nari, with which, as has just been noticed, 
bands containing Gaj fossils are interstratified, has been drawn at the base of the 
limestones. At one sj)ot, a thickness of 500 feet, entirely composed of limestone, 
was measured (by aneroid) at the base of the groiTjT, and this thickness seems 
to include the greater jTortion of the Gaj strata in this locality. 
It has already been mentioned that the supposed unconformity between the 
Gaj and Nari groups west of Sehwan at Tandra Rahim Khan jjroves, on further 
examination, to be doubtful. But the Gaj group in the country south of Sehwan 
comjrletely overlajTs the Nari in places, and rests upon Khirthai' beds. In this 
country, however, the Gaj itself is but poorly represented, and frequently is 
either entirely wanting, or appears as merely a thin band at the base of the 
Manchhar group. 
The passage from Gaj to Manchhar, despite the unconformity .shown by over¬ 
lap, and the presence of Gaj pebbles in Manchhar beds, is locally just as complete 
as any of the other cases of transition already mentioned. In the paper pub¬ 
lished in 1870, the transition beds containing estuarine shells in the Khirthar 
range were mentioned. Some of the estuarine shells are by no means confined 
to this belt; Corbula trigotudis, for instance, occurs in beds near the base of the 
Gaj group, and has also been found in one band in Manchhar rocks, about 300 or 
400 feet above the top of the Gaj. As will be shown presently, there is in 
the neighbourhood of Karachi even stronger evidence of the close connection 
between Manchhar and Gaj beds. 
Although the number of Gaj fossils have been somewhat increased, the 
additions have been less extensive than in the case of many of the other gi’oups. 
