EAST-INDIAN ARCHIPELAGO. 
235 
which is generally shallow, even in places where the land 
seems to be somewhat precipitous, I have not coloured 
them. Houtman’s Abrolhos (lat. 28° S. on west coast) 
have lately been surveyed by Captain Wickham (as described 
in Naut. Mag. 1841, p. 511) : they lie on the edge of a 
steeply-shelving bank, which extends about 30 miles sea- 
ward, along the whole line of coast. The two southern 
reefs, or islands, enclose a lagoon-like space of water, 
varying in depth from 5 to 15 fathoms, and in one spot 
with 23 fathoms. The greater part of the land has been 
formed on their inland sides, by the accumulation of frag- 
ments of corals ; the seaward face consisting of nearly bare 
ledges of rock. Some of the specimens, brought home by 
Captain Wickham, contained fragments of marine shells, 
but others did not ; and these closely resembled a formation 
at King George’s Sound, principally due to the action of 
the wind on calcareous dust, which I have described in my 
work on Volcanic Islands. From the extreme irregularity 
of these reefs with their lagoons, and from their position 
on a bank, the usual depth of which is only 30 fathoms, 
I have not ventured to class them with atolls, and hence 
have left them uncoloured . — -Boivley Shoals : these lie 
some way from the N.W. coast of Australia : according to 
Captain King (Narrative of Survey, vol. i. p. 60), they are 
of coral-formation They rise abruptly from the sea, and 
Captain King found no bottom with 170 fathoms close to 
them. Three of them are crescent-shaped ; a third oval 
reef of the same group is entirely submerged (Lyell, 
Principles of Geolog., book iii. chap, xviii.) ; 1 coloured blue. 
— Scott’s Keefs, lying north of Rowley Shoals, are briefly 
described by Captain Wickham (Naut. Mag., 1841, p. 440) 
as of great size, of a circular form, and ‘ with smooth 
water within, forming probably a lagoon of great extent.’ 
There is a break on the western side, where there probably 
1 [Book iii. ch. xlix. 11th edition.] 
