166 PEOCEEDINGS OP THE GEOLOGICAL SOCIETY. [Jan. 27, 



plate set at right angles to the course of the dyke. These plates 

 appear to he of different material from the dyke itself 5 and where 

 this affects the needle they do not partake of that quality. In aspect 

 these selvages resemble greenstone, although so closely connected 

 with the basalt. They may, no doubt, represent a band of trap, 

 fused by the dyke, or more probably a part of the dyke itself, 

 which, under electrical action, has assumed this structure. 



The general direction of the dykes is more or less nearly parallel 

 to the bands of volcanic vents, main or subordinate, near to which 

 also they are most numerous. Hence, although this rule has, as 

 was to be expected, many exceptions, the greater number of the dykes 

 near to the central axis of the Concan range north and south, and 

 those near the subordinate band in the Malseje Yalley range more 

 nearly E.jN.E. and W.S.W. In both, as in the adjacent districts, 

 occur a few dykes taking other directions ; but out of thirty-nine 

 dykes, thirteen range north and south, and sixteen between N.E. 

 and E. and S.W. and W. Three only He S.E. and N.W. 



The plane of each dyke is usually vertical ; and the exceptions are 

 few and local. Also they range in straight or nearly straight lines. 

 They now and then swell out or contract, and in one or two instances 

 have been observed to include a rider, though commonly their faces 

 are parallel. They are very seldom indeed connected with any ver- 

 tical displacement of the rocks ; and the few exceptions to this are of 

 very limited extent. I have not observed any dyke to be connected 

 with a considerable fault. 



Though the basalt of the dykes is peculiarly hard, and undergoes 

 very little disintegration from the weather, its fissile character leaves 

 it with little power of resisting eroding forces ; and, in consequence, 

 although sometimes a dyke stands up, out of the trap ridge already 

 described, as a rugged black wall, more commonly its position is 

 marked by a depressed furrow along the top of the ridge, the sides 

 of which are thickly strewed with its fragments. 



The most precipitous passes across the Ghauts are those produced 

 by the removal of the dykes. In such cases the pass is a vast 

 fissure, the walls of which are perpendicular and parallel, some- 

 times 300 or 400 feet high, and not above 10 or 20 feet apart. 

 These walls are almost as hard as the removed basalt, and, not being 

 fissile, are much less readily disturbed. Here the lower or unre- 

 moved part of the dyke forms the rough steps up which such passes 

 are ascended. The "Msnee cha Dara," or "pass of stone," near 

 Jooneer is a very fine example of such a pass. 



Owing to this same hardening of the trap, the course of a dyke 

 across a river is often marked by a bund or dam, which the people 

 turn to advantage for the irrigation of their lands. There are 

 several such near Moorbar ; and the navigation of the Callian river 

 is seriously impeded by such an obstruction a few miles below that 

 town. 



These dyke ridges form rather a leading feature in the topography 

 of the Concan. Some resemble raised causeways, and are so used 

 during the rains : others have all the regularity of an artificial 



