208 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



A chalk-deposit* is to be found, by all accounts, in the diiferent 

 basins or lagoon bottoms in every principal group, though nowhere 

 so extensively as along the western coast of Andros Island, where 

 it may almost be termed a young chalk formation. The extent of 

 this local chalk-deposit is considerable ; at its eastern limit it abuts 

 against a narrow ridge of hills along the centre of the islands ; the 

 western shore of the islands is generally a stiff chalk bank, 4 or 5 

 feet high, sloping inwards to the marshy chalk-flat f, which is well 

 overgrovm with mangroves, &c., and reaches to the foot of the 

 western slope of the hill-range above-mentioned. Parallel to this 

 western coast and seaward, with a breadth of 14 or 15 miles, the 

 chalk continues in mass as an anchorage ; westward again of this, 

 the white mud thins out as a mere covering to the sandy bottom, 

 but stUl thick enough to preserve the whitish colour over a rudely 

 heart-shaped space of about 80 miles in length by 60 in extreme 

 breadth. The next largest chalk-deposit (but far less in extent) is 

 that in the harbour of Green Turtle Cay. 



The "red earth" previously mentioned as forming, generally 

 speakmg, the scanty soil of the Bahamas, is at times interstrati- 

 fied with the rock, and sometimes it is incorporated with it. It is 

 identical with the "red earth" of the Bermudas;]; (specimen No. 1.5) 

 which proved a considerable source of embarrassment, especially with 

 reference to Ireland Island, by seeming to point out alternations 

 of aqueous and other deposits, which were contradicted by the pre- 

 sence of the characteristic Helix in all the beds. In visiting a 

 cave near Delaport in 1849, Capt. Nelson found the bottom of the 

 cave for many feet in depth covered with a loose dry " red earth," 

 in grains varying in size from coarse sand to fine dust (specimens 14 

 & 14 a, h). Under the microscope this appeared as a mass of 

 insect-remains, the rejectamenta of Bats living in these caverns. 

 Specimens of the earth from another part of the same cave, how- 

 ever, were so much altered in character, that they resembled the 

 Bermuda "red earth," and afforded a complete clue to the charac- 

 ters of this substance. Some of the varieties from the Delaport Cave 

 were examined microscopically and chemically by Professor Quekett, 

 of the Royal College of Surgeons, who not only confirmed the above, 



* Admiral Roussin compares the chalk, or tuf blanc, occurring in many places 

 along the coast, for the space of 1300 miles from the Abrolhos Islands to Maranham, 

 to mortar ; and this expression is aptly descriptive of the " chalk " of the Baha- 

 mas (see also Berra. Mem. I. c. p. 114. There was, however, more of the pure 

 white kind at Bermuda). This calcareous mud is derived not merely fi-om the 

 comminution and decomposition of Corallines and Corals, and from the exuvicB of 

 Foraminiferae, Molluscs, Echinoderms, Crustaceans, &c., but also from the faecal 

 ejectamenta of Echinoderms, Conchs (see p. 212, note), and coral-eating Fish 

 {Scari, &c.). At Bahamas the Angel fish and the Unicorn or Trumpet fish are 

 common feeders on shells and corals. The Lahridm, RaiidcB, and other fishes are 

 active agents in the comminution of shells. For remarks on the Cat-fish, see Quart. 

 Journ. Geol. Soc. vol. vii. p. 201, note. 



t This soft chalk-flat surrounds the freshwater lake of Andros Island, and is 

 inhabited by " colonies " of Flamingoes who build their conical nests in great 

 numbers here, as well as in other parts of the Bahamas. 



+ Bermuda Memoir, loc. cit. p. 105, 108. 



