168 PKOCEEDIJSTGS OF THE GEOLOGICAL SOCIETY. [Jan. 27, 



The dykes are observed to traverse and to pass at tangents to 

 particular vents, and, 'although most numerous about such points, 

 not to radiate from them. Nor do such vents present any traces of 

 a flux of regular basalt. From this it seems reasonable to infer 

 that the dykes are due not only to a later period, but to a period 

 after the cessation of the regular eruptive action, and possibly 

 therefore that the capping beds may be the overflow of the dykes. 



Salsette, indeed, seems to be an exception, and to contain evidences 

 of still later eruptive action, though local only. 



The dykes themselves seem to admit of division into at least two 

 periods, since dykes of different grain frequently intersect each 

 other. Near Moorbar these intersections are most numerous ; but 

 at such points the rock is commonly very loose, covered with jungle, 

 and full of poisonous snakes ; they are therefore difficult of examina- 

 tion. I think, however, that in many cases the dykes lying north- 

 east and south-west traverse and often very slightly dislocate those 

 lying more nearly north and south ; whence I infer these to be the 

 later, and the cross band of the Malseje vents to have ejected its dykes 

 since those connected with the general outline of the Ghauts. It 

 is probable, however, that a minute examination of specimens from 

 all these dykes would throw more light upon this matter. 



The dykes, as has been stated, are neither vesicular nor amyg- 

 daloidal, although they pass through rocks most of which are both 

 one and the other. But though the basalt contains no vesicles, it 

 is fissured in all directions, and must have been fissured, more or 

 less, very soon after it was poured out, as it began to cool. All the 

 contiguous rocks contain kernels of zeolite, and now and then of 

 chalcedony and calcareous spar. None of these minerals are found in 

 the basalt, although its cracks must have lain open to receive them. 

 I do not know what is the prevailing theory upon the deposition of 

 these included minerals; but these appearances seem to point to their 

 segregation from the trap, and to be opposed to any theory of infil- 

 tration. 



Among the dykes alluded to as not basaltic may be mentioned 

 one on Trombay Island, which branches off from a basalt dyke, but 

 is quite void of the mineral, and contains laumonite. 



In most cases the great and numerous fissures, so common on the 

 Ghauts, mark the passage and removal of a dyke. This is not 

 always the case ; and hence there seems ground to suspect that the 

 fissures may have been formed, not by the forcible injection of the 

 basalt, but independently of and before its appearance. 



• . DiSCTJSSIOK. 



Mr. David Foebes did not see any proof of the dykes being of 

 different ages. In modern eruptions, lasting over some years, the 

 lava first erupted sometimes became fissured, and the fissures filled 

 at a later period of the eruption. 



