Page:Quarterly Journal of the Geological Society of London, vol. 25.djvu/258

164 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Jan. 27, These features naturally divide the country into the district above the escarpment, called the Deccan, and that below it, called the Concan. The escarpment itself is known as the Syadree Range or Western Ghauts.

The Ghauts, therefore, are a vast escarpment and not a regular mountain-range. Upon this escarpment, however, there occur mountains of from 4000 to 5000 feet high; and connected with it there are several long and lofty hill-ranges, passing from it eastwards and declining as they recede.

The escarpment, generally precipitous, contains several special precipices of from 1000 to 2000 feet in height, the crests of which are at least as far advanced as their bases, and in a few very remarkable cases, as at Hurreechunder, actually overhang them.

For many miles north and south of Bombay, and for many miles inland, the rocks of the district are, with limited exceptions, of igneous origin, and varieties of trap.

It is not the object of this paper to explain the general geology of this district; but it may be observed that there is evidence to show that a line or band of volcanic vents extends north and south up the axis of the Concan, whence most of the trap of Western India appears to have been poured out,—eastward, at a moderate slope to form the Deccan; westward, at a much steeper inclination, into the sea. There are also appearances connected with these vents which seem to explain the great and sudden difference of altitude between the country above and that below the Ghauts, as well as the singular fact that the Ghauts themselves do not appear to have been produced by, or to be in any way connected with, any line of upheaving, or of fault, or with any similar disruption or displacement, local or general.

The dykes under consideration are no doubt mineralogically interesting; but they are far more so from their connexion with the various vents in the great volcanic band, and because they form a part in the chain of evidence upon which the theory of the formation of this very remarkable part of India must rest.

The dykes by which this part of the Concan is traversed vary in breadth from one and two to ten, twenty, forty, and occasionally 100 or 150 feet, and are often many miles in length. They are most numerous about the centre of the Concan. They are also numerous in the great valley or bay known as the Malseje Ghaut. They are seen, though less frequent, beneath the Nana, Copolee, and Beema-Sunker Ghauts, and in the road between Panwell and the Bhore Ghaut. Many occur upon the Ghauts themselves, and a few above them upon the high tableland of the Deccan. They have also been, traced in the islands of Bombay and Salsette.

The contents of a few of these island dykes, and of one or two upon the shores of the Concan, are altogether peculiar; but with these rare exceptions the dykes present very many points of resemblance. They are basaltic; all have a tendency to the prismatic form, which now and then, as at Gorabunder, in Salsette, and at Callian, becomes columnar. The axes of the prisms are always at