1 835.] Geology of the Bombay Islands. 29 1 



Article VI. 



Sketch of the Geology of the Bombay Islands. By 

 Robert D. Thomson, M. D. 



Although Bombay has been known to Europeans since the 

 year 1509, when the Portuguese Viceroy Ameyda captured 

 a vessel in what the historian of the time has termed " the 

 River of Bombaim," # no connected view of the geological 

 nature of the islands and antiquities in its neighbourhood 

 has hitherto appeared. It is with a view of contributing to 

 supply this omission, that the facts contained in this paper, 

 which were acquired by observation, in the course of a short 

 residence in that presidency in 1832, were drawn up. 



The mean of fifty-nine observations in May, June, and 

 July, 1832, gave me 83°* 14' for the temperature of the 

 harbour of Bombay. This includes twenty-seven observa- 

 tions made after the setting in of the monsoon, on the 14th 

 June. But a period of thirty-two days, immediately previous 

 to this' date, affords 83°-43' for the mean temperature of the 

 hot season; and twenty-seven observations gave for the 

 commencement of the rainy season a mean temperature of 

 82°* 85. The average temperature for 1803 was 81|°, and 

 for 1804, 80J° ; and the number of rainy days for these 

 years 102.f 



The quantity of rain which fell in June, July, August, 

 and September 1817, was 104 inches.^ On the 23d June 

 1817, no less than 93 inches of rain fell in one day. In 

 fact, the inhabitants of temperate countries can form no 

 idea of the quantity and force of the rain which falls 

 between the tropics. The mean barometrical height for 

 half of 1816 and 1817, was 29'986 inches. 



The harbour of Bombay, situated on the Concan, or 

 Pirate Coast of the western peninsula of Hindostan, is 

 possessed, as its name implies, of peculiar excellence and 

 capaciousness,^ and has, therefore, been considered of great 

 value ever since it became part of the British possessions. 

 It may be described as forming the southern portion of a 



* Sousa's " Portugues Asia," Tome. i. p. 146. 



f Ann. of Philosophy, xiii. 145. 



t Ann. of Philosophy, xii. 212. 



§ From the Portuguese Buon-Bahia, good hay. The accompanying chart of 

 the harbour and islands of Bombay, I have enlarged from that of Laurie and 

 Whittle. 



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