XXIII. — Geological Observations made on a Voyage from Bengal to Siamand 

 Cochin China. Extracted from a Letter to H. T. Colebrooke, Esq. M.G.S. 



By J. CRAWFORD, Esq. M.G.S. 



[Read December 3th, 1823.] 



VV E left Calcutta in the end of November 1821, and proceeded down the 

 Bay of Bengal and the Straits of Malacca to Singapore. We then stood 

 across to the coast of the island of Borneo, and from thence to the point of 

 Kumboja. From this place, until we made the river of Siam, we passed 

 through the innumerable and almost unknown clusters of islands which skirt 

 the east coast of the Siamese Gulf. We continued at Siam four months, and 

 left it in July 1822. From thence, passing down the Gulf of Siam, we pro- 

 ceeded to Cochin China. Having reached the Bay of Turon, we visited Hue, 

 the capital of Cochin China ; thence we returned by land to Turon, a distance 

 of 60 or 70 miles, and finally quitted Cochin China in October 1822. 



During this voyage I had an opportunity of forming a small collection of 

 specimens, and making some observations which may, I hope, contribute to 

 throw light on the geology of several of the places which we visited. 



The Seyer Islands in the Bay of Bengal, as also the opposite coast of Tan- 

 nasserim in such parts as fell under my examination, consist of granite, con- 

 taining in it beds of porphyritic greenstone. The same primary formation 

 continues to Junk Ceylon, Prince of Wales's Island, and the islets around it, 

 down to Dinding in the Straits of Malacca. Cape Rachado, a hilly promontory 

 nearly halfway down the straits, we found to consist of quartz. The foun- 

 dation, at and about the town of Malacca, is cellular clay iron ore ; but the 

 mountains of the interior are of granite. The Carimon Islands in the Straits 

 of Malacca are formed of compact felspar ; limestone also occurs in them. 



At Singapore, a secondary formation is discoverable, and varieties of sand- 

 stone and shale form the principal rocks, together with conglomerate argilla- 

 ceous sandstone, and gray limestone. 



The great chain of primitive mountains which stretches along the length 

 of the Malayan peninsula, ceases 30 or 40 miles before reaching its extreme 

 point. This point, in the parts which I have examined, consists of felspar 

 porphyry. Of the Malayan peninsula, I may further observe that on the west 



