Page:Quarterly Journal of the Geological Society of London, vol. 26.djvu/218

118 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 2. A few Remarks on the Geology of the Country surrounding the Gulf of Cambay, in "Western India. By Alex. Rogers, Bombay Civil Service.

(Read June 23, 1869*.) The rapid silting up of the Gulf of Cambay gives particular interest to an inquiry into the geological conditions which probably shaped it in remote ages, and the gradual changes which have modified its original form, and brought it to its present state. The geological features of the country surrounding the Gulf afford, when taken as a whole, an unusually clear clue to the nature of some of these changes, and may assist us in tracing what may have taken place in the region between the head of the Gulf and the present mouths of the Indus, and in the desert between Rajpootana and Sind. The former comprises within itself the Great Runn of Cutch, which has already received much attention from the most distinguished geologists. It will be seen, from the accompanying rough geological map of the Gulf and its neighbourhood (fig. 1), that primary or metamorphic rocks are traceable in its immediate vicinity only in a small tract on its west coast. Here they appear in isolated peaks of from a few to two or three hundred feet in height above the alluvium that surrounds them near Chumardee, but are also found on and below the general level of the country for about fifty miles to the north and north-west of that village. They also appear on the east of the river Myhee to the north and north-west of the hill of Powaghur in a precisely similar position with reference to the surrounding country to those on the west of the Gulf. In both these localities even the highest points of the granite peaks show signs of weathering, and probably also of the erosive action of waves. The same effects being visible down to the present level of the country, and detritus derived from the long-continued denudation of the higher rocks having in some cases accumulated round their base to a considerable depth, prove that the raising of the level of the land, the cause of the granitic rocks now appearing as islands in a sea of alluvium, must have occupied immense periods of time. Granitic and metamorphic rocks appear in regular ranges, and extending over large tracts of country, for the first time fifty or sixty miles north-east of Ahmedabad, or fully a hundred miles from the head of the Gulf, running in an easterly and north-easterly direction. Between these and the desert that lies between Rajpootana and Sind to the north-west, and as far as Cutch and Kattywar on the west and south-west, there is not a rock to be found; all is deep alluvium, of consistencies varying from that of almost pure siliceous sand to that of the rich light-coloured "Goraroo" soil of Goozerat (which may in some places be cut almost as butter may with a knife), and the deep black "Regur" or cotton soil. Through this alluvium the Saburmuttee and other rivers cut their way, frequently exposing sections of 20 feet or 30 feet in depth without a trace of stone in

Journal.
 * For the Discussion on this paper see p. 441 of the last volume of the