of the Bay of Bengal &c. O77 
depths with a short outline of the hydrography of the basins 
themselves. 
Bay of Bengal.—The boundaries of the Bay of Bengal on 
the north and west are too well known to need mention ; but 
the exact delimitation of its basin from that of the Andaman 
Sea has only recently been fixed with exactitude by Com- 
mander Alfred Carpenter, R.N., D.S.O., in charge of the 
Indian Marine Survey, to which highly scientific officer I am 
indebted for much more than the facts alone. 
On looking at a chart of the Bay of Bengal, a chain of 
islands (the Preparis, Ceros, Andamans, and Nicobars) is seen 
to extend, with a slight western convexity, from north to 
south between Cape Negrais in Burmah and Acheen Head in 
Sumatra. And on referring to Captain Carpenter’s Contour 
Map of the Bay (véde ‘ Administration Report of the Marine 
Survey of India for 1888-89 ’) all the contour-curves are seen 
to converge ultimately within a hundred miles of the western 
coast of this chain. Quite close to the eastern shore of the 
chain we find, in the Andaman Sea, depths of from 1100 to 
1200 fathoms, while in the channels between the islands, 
which connect the two seas, the depths range from 150 to 
760 fathoms. This is conclusive proof of the existence of 
two distinct basins, separated by a comparatively narrow ridge 
rising into the isolated island peaks of the Andamans and 
Nicobars. 
The Bay of Bengal thus defined touches in its extremes 
the meridians between 80° and 94° KE. It has a maximum 
depth at its mouth of nearly 2400 fathoms, and its minimum 
temperature hitherto recorded (at 2105 fathoms) is 33°7 
Fahr., corrected for pressure (Carpenter, ‘ Mean Temperature 
of Deep-waters of Bay of Bengal,” Journ. As. Soc. Beng. 
vol. lvi. pt. ii. no. 2). 
In the northern part, into which the great rivers of India 
and the eastern ultra-Himalayan region pour their muddy 
waters, and almost as far south as the 1600 fathom contour, 
the specimens of the bottom obtained by the ‘ Investigator ’ 
consist of varying grey, green, blue, and brown muds, with 
comparatively few constituents of direct organic origin; but 
in the southern and more open part the ‘ Investigator’ has 
almost always found G'lobigerina-ooze (Globigerina, Orbulina, 
and large Pulvinulina). Running through the shoal-water at 
the extreme northern end, opposite the middle of the Brahma- 
putro-Gangetic Delta, is the Swatch of No-ground. This, 
which has a direction tairly N.N.E. and 8.S.W., is a narrow 
deep channel of over 300 fathoms in a sea of under 100 
fathoms, and is reasonably regarded by Captain Carpenter 
as the “ scour” of the rivers. 
