166 



Sketch of the Geology of the 



[Jan. 



powering influence of the solar rays, " vim solis umbrae leevant." The 

 coast, is low and rocky with the water gradually shoaling to the land, 

 which at ebb tide leaves a dry and pleasant beach. The amygdaloid 

 shews itself frequently in the form of half sunk rocks and dangerous 

 ledges, especially along the Coulaba shores, but suffering in the lapse 

 of time from the action of the sea, and occurring remarkably in con- 

 junction with the clay-stone porphyry, the latter often rising up be- 

 tween two rounded masses of the former, sometimes placed above it, 

 at other times under it, both being traversed frequently with basaltic 

 dykes. All these rocks at the shore may be observed covered with 

 shells, and their surface with a decomposed powdery matter, which on 

 inspection turns out to be the basis of the rock crumbling into dust. 

 At the distance of two miles from the town, many of the shells which 

 abound so profusely on the sea-shore are calcined, by which process, 

 they are converted into caustic lime, which the natives term chunam, 

 a substance in great request, both as a mortar, and as an edible rolled up 

 in the betel leaf The latter habit, which has been denominated by 

 some writers a luxury, ought rather to be termed a necessary practice, 

 as we find it prevailing wherever the sole articles of diet are procured 

 from the vegetable kingdom, the different substances employed fulfill- 

 ing the same end, whether it be on the coral rocks of the Pacific, the 

 arid deserts of Africa, or the interminable forests of America. 



Salsette Island. 



The description of the geological structure of one of ttiese islands, 

 may be said to include almost the particulars of the whole, but for 

 the sake of greater perspicuity, we have ventured to consider them 

 separately. The essential composition of Salsette, is clay-stone por- 

 phyry and amygdaloid, corresponding with those rocks in Bombay, but 

 basalt occurs in very considerable tracts, and assumes more decided 

 forms. The island is very irregular in its surface, consisting of 

 ridges and intervening valleys, which in combination afford agreeable 

 scenery. 



The basalt forms two ridges which run parallel to each other, the 

 one on the west and the other on the east of the narrow strait which 

 separates the island from the continent, appearing above the amyg- 

 daloid which forms the base of the hills ; and therefore, leading us to 

 conclude, that its ejection has been subsequent to that of the amyg- 

 daloid. 



The alteration which the eruption of the basalt has produced on the 

 masses through which it has been forced, by rendering the two rocks 

 at the point of contact similar, and as if passing into each other by a 

 gradual transition, are sufficiently obvious, but at the same time, the two 

 varieties are as distinct as any of the projected series in general appear, 

 so that in a theoretical nomenclature (the establishment of which, it 



