68 
Records of the Geological Survey of India. 
[VOL. VIII. 
In explorations of this nature it is commonly the case that some approximation can be 
made towards computing the depth at which the object should bo attained. The simple 
general rule is — from the proposed point of experiment to follow the descending section 
directly across the strata to the outcrop of the hod sought for; and then, from the surface 
distance and the mean dip of the rocks, to calculate the depth from the surface at the required 
point. Were this rule to hold good in the present case, the coal would he hopelessly out of 
reach where we are now seeking for it. Throughout this whole central area of the rock 
basin, the strata have a very constant northerly slope to within a short distance of the north 
boundary, where, according to the above rule, the dept h to the measures would be enormous. 
The rule, however, works upon the assumption that the beds continue to the deep as they 
appear at the surface; and it is quite certain that this is not the case with the rocks we havo 
to deal with here. They are for the most part massive, irregular sandstones ; and it is 
demonstrated that not only individual beds, but whole groups of beds, die out to the deep and 
arc overlapped before reaching the north side of the basin. There is no law known, or in 
the nature of the case possible, for such a mode of extinction and succession of stratified 
deposits. Their distribution depends upon the local physical conditions at the time of their 
formation, the only evidence for which conditions is to ho found in tire deposits themselves. 
Thus, there can he no reason assigned why the coal-measures themselves should not also die 
out to the north, they being composed of thick sandstones not unlike those above them. 
The hope that such is not tho case rests upon the features along the north boundary, as 
already noticed. 
The facts bearing upon this class of explorations have also been given and discussed in 
some detail in my last report on this ground; but from tho foregoing brief remarks it can 
be seen that these trials, though under such very different conditions, are of a scarcely less 
precarious nature than are those in the open valley. It may also here be understood that 
any offhand opinion ou the point can be of no value, unless in so far as it may be based upon 
reasons such as those indicated. 
In selecting sites for these borings, I gave, as for the others, a wide berth to the known 
difficulties close to the general boundary of tho field; such as, firstly, the greater disturbance 
of the strata, often with trappean intrusion ; secondly, the coarsely couglomeritic character 
of the Mahadovas in this zone, which has proved so obstructive to borings at Mohpani; and 
thirdly, to give a better chance of getting below the known overlap. To these considerations 
the surface features added other inducements. On tho east and west of the basin, two wide 
open areas are presented in the valleys of tho Dudhi and tho Tawa, separated from the 
plains of the Narbada valley by a narrow belt of low hills. If the Satpura coal-basin over 
fulfils our reasonable hopes as regards coal, it is in these areas that tho industry would be 
established, and here that it should be started. Whether or no coal should be found some¬ 
what nearer the surface towards the edge of the basin, it would be a duty to ascertain if 
it lay within reach of these central areas whore mining must be located if it is ever to 
expand; hut to fulfil this purpose the borings hero should be carried to the full depth at 
which there would be any prospect of mining being profitably carried out. Upon this 
point my knowledge and experience scarcely entitle me to an opinion : I should say conjectur- 
ally, that supposing coal to be present, it would pay better in the long run to work it 
at 150 fathoms in the centre of the field than at 50 fathoms near tho margin. 
In commencing operations, preference was given to the Dudhi area, for tho reason that 
„ . _ „ tho strongest natural outcrops of tho coal both to north and south 
T)udhi Valley. ^ ^ 
were ou the east side of tho basin. The borings at Ivhapa 
and Manegaon were commenced in the middle of February 1874. Both start in tho Denwa 
horizon of the Mahadeva series. At the close of the season, on tho 1st Juno, they had 
reached the depths of 260 and 242 feet. After the stoppage of the Sukakheri boring, work 
