PART 4.] 
Theobald: Raised Oyster Ranh. 
Ill 
actual sites for borings in the positions now recommended, the point may be decided entirely 
with reference to the convenience of surface conditions for the operation, the geological 
data being so vague as to leave the exact point immaterial within a considerable range; only, 
give a wide berth to trap dykes. 
The discussion of last season’s observations on the north boundary of the Satpura basin 
lias led to an inference of the possibility of coal being found in the Narbada valley itself. 
Shallow borings through the alluvial deposits would show whether these were underlaid by 
the metamorphics, or by formations belonging to the coal series. I would recommend 
Gadurwara and Bankeri as suitable positions for this experiment. 
H. B. MEDLICOTT. 
August 1872. 
Note or the value of the evidence afforded by raised oyster barks or the 
coasts of India, ir estimating the amount of elevation indicated thereby, 
by W M. Theobald, Geological Survey of India. 
In a paper in the Records of the Geological Survey, Part 3 of 1872, on the 
geology of the Bombay Presidency, Mr. Blanford quotos some observations made 
by myself in 1858, establishing the elevation of a portion of the Kattiawar coast during 
very recent times, and it is with reference to some of the evidence adduced in support of this 
assertion, and in order to correct an error caused by misreading of my notes, that I would 
here offer a few remarks. Mr. Blanford ( loc. cit.), page 101, makes my estimate of the 
rise in the coast that took place in 1856 to amount to ten feet, a misreading for two, 
the words used by me being as follow:— 
“Many of these oysters are seen with both valves attached, and evidently but recently 
dead; and as oysters of this size are never uncovered, I presume that an elevatory move¬ 
ment of at least two feet, and probably more, took place in 1856, the year when all the 
oysters in the creek were destroyed”. Of course a clerical error of this sort is very easily 
made, and in this instance the actual amouut of elevation that took place may in reality 
have been nearer ten than two feet. The evidence, of course, of the occurrence of oysters 
of a sort never exposed by spring tides above low water mark is conclusive, but does not 
permit a very exact gauge as to its amount. There is, however, another point connected 
with the question on which I would record a caution. There are on the eoasts of India three 
species of oysters which are likely to be made use of in determining questions of littoral eleva¬ 
tion, viz., the creek oyster, the shore oyster, and the rook oyster. The creek oyster is a 
large species something like the fossil O. lingula. Sow., and possibly, Dr. Stoliczka thinks, iden¬ 
tical with O. Talienwahensis, Crosse, and attaining occasionally the length of a foot. It is ex¬ 
cellent eating and universally esteemed, but it is only procurable at the springs, as it rarely 
occurs in less depth than a little below lowest spring tides, and never, as a rule, above that 
level. 
The second species is, in my opinion, merely a variety of the last, and Mr. Hanley, (o whom 
I submitted specimens, declared they were barely distinguishable from the European O. 
edulis, L. This species occurs sporadically between tide-marks botli on the coast of 
Kattiawar and the eastern shores of the Bay of Bengal, in common with both the other 
species, and from its sparse mode of occurrence is, in my opinion, merely an abnorma form of 
the first, reduced in size and altered in appearance by the uncongenial surrounding amidst 
which it has been developed. A specimen collected by myself of this form is figured as 0. 
nigremarginata, Sow. in Conch. Iconica, Plate XXXIII, 84. The third species is the little 
