1837.] Sketch of the Geology of the Bombay Islands. 153 



XIII. — Extracts. 



I.— 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 con- 

 nected view of the geological nature of the islands and antiquities in 

 its neighbourhood has hitherto appeared. It is with a view of contri- 

 buting 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 observations made after the setting in of 

 the monsoon, on the 14th June. But a period of thirty-two days, imme- 

 diately previous to this date, affords 83° 43' for the mean tempe- 

 rature 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 was8U°,and for 1804, 801° ; 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.J On the 23d June 1817, no less than 9-3 inches 

 of rain fell irfone day. In fact, the inhabitants of temperate coun- 

 tries 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 con- 

 sidered of great value ever since it became part of the British possessions. 

 It may be described as forming the southern portion of a rectangular 

 bay or recess, which lies between Tull Point in N. lat. 18° 47' 

 and Basseen, in N. lat. 19° 19', and between the parallels of E. long. 

 72° 47' and 73° 3', possessing, therefore, an extreme length of 

 thirty-two miles, and an average breadth of sixteen miles. The 

 island of Salsette occupies seventeen miles in the length of the northern 

 part of the bay, acquiring a breadth of from fifteen to seventeen miles, 

 while its circumference has been computed at seventy miles. 



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

 + Ann. of Philosophy, xiii. 145. 



* Ann. of Philosophy, xii. 212. 



\ From the Portuguese Buon-Bahia, good bay. The accompanying chart of the harbour 

 and islands of Bombay, I hare enlarged from that of Laurie and Whittle. 



