120 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 
miles to the south and south-east of the former near its mouth, and on 
the west bank of the latter to about halfway between Ahmedabad and 
the head of the Gulf, the soil is all light-coloured, containing particles 
mostly derived from the primary and metamorphic rocks to the 
north-east. The black soil lies in one extensive bed to the west of 
the last-mentioned limit of the light-coloured soil, widening out on 
both sides towards the mouth of the Saburmuttee, and down the west 
coast of the Gulf, but becoming lighter after it reaches the granitic 
region. This westerly belt stretches beyond the head of the Gulf as 
far at least as the Lesser Runn, and probably impinges on the Great 
Runn itself. The alluvial soil to the north of Baroda,. between the 
Myhee and the trap range running to the north-east from Powaghur, 
beyond the Champaneer beds mentioned by Mr. Blanford, is of a 
general character between those of the light-coloured and black 
varieties; and the deltas between the mouths of the Myhee, the 
Nerbudda, the Taptee, and a point about fifty miles to the south of 
Surat, where the trap touches the present coast-line, are again all 
black. 
We have now to consider whence these enormous alluvial deposits 
can have been derived. With regard to those on the east. coast of the 
Gulf of Cambay, there can be no hesitation in ascribing them to the 
gradual action of the two large rivers Nerbudda and Taptee, and the 
numerous smaller streams which flow from the east, either from the 
western range of Ghauts or passing through gorges in that range 
from further east. There is no doubt that the washings of the 
trap-rocks which compose that range enter largely into the com- 
position of the black soil which, as already stated, occupies almost 
the whole of the east coast of the Gulf; for much of the trap is amyg- 
daloidal, and zeolitic minerals derived from it are found in abund- 
ance in the soil. But this cannot be said of the light-coloured soil 
on the north-east of the Gulf, which must be chiefly derived from the 
primary and metamorphic rocks in that direction mentioned above— 
or of the black belt running from the head of the Gulf in a north- 
westerly direction, in which there are no rock formations at all to 
account for the colour of the soil. It is as well to notice here that 
the fact of this belt being just of as dark a colour as that lying 
on the east coast apparently militates against the theory that this 
colour is derived from the presence of iron in the trap-rocks from 
which it is believed to be formed. The Myhee, the Saburmuttee, 
and other streams which now fall into the Gulf at its northern ex- 
tremity are not sufficiently large to account for the deposit, espe- 
cially for the belt of black soil to the north-west, extending as far 
as the Lesser Runn. Many considerations point to the existence in 
former ages of some large river flowing down from the north, and 
falling into the Indian Ocean somewhere in the position of the pre- 
sent Gulf of Cambay; and it is not improbable that that river may 
have been the Indus. It may have been that the original course of 
the Indus from the Punjaub was in a more south-easterly direction 
than that of the present day; or it may from the first have had 
several mouths, some in the position of its existing delta, others 
