i\2 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



abundant at Bermuda) supplies chalk. Gorgonics (many species) 

 aiford strong connecting and retentive bonds, Pahnipora alcicornis^ 

 (specimens 17 & 18) is always a remarkably accretive agent, and it 

 contributes also a soft sand. Echinoderms and Crustaceans are also 

 abundant, supplying fragments and soft sand. Serpulcef contribute 

 extensively in mass and othervdse. 



Of Mollusca, the Sti'ombus gigasX, Tiirho pica^, Venus (Lucina) 

 Pennsylvanica ||, and Piqm chrysalis^ are some of the most important 

 contributors, both in mass and as sand. The bones of Fish and 

 Reptiles {Chelone midas, C. caretta, and probably the Alligator**), 

 are more or less abundant, but are soon triturated into soft sand and 

 mud. 



Lastly, as regards the contributory agency of animal life in the 

 increase of the land, mention was made at p. 209 of the fact of Birds, 

 Bats, and Insects having added very considerably to the soil and 

 rock of these islands. 



7. Elevation and depression of the land. — Whatever may be the 

 real foundation of the Bahamas, — whether, like the West Indian 

 Islands generally, they are indebted to igneous agency for their 

 existence as elevated masses, or otherwise, — there is no evidence of 

 such elevation ha^ang taken place either in the Bahamas or Bermuda. 

 On the contrary, the total absence of coral-reefs in mass, or even of 



* This Zoophyte ? is most abundant at Bermuda, but not very plentiful at the 

 Bahamas. 



•f See Berm. Mem. /. e. f. 18. p. 117 ; and Bermuda specimens Nos. 40 & 41 ; 

 also Bahama specimens in the Society's Museum. Capt. Nelson observes that 

 the Serpuline reefs, though at first merely incrustations, become thick masses, 

 very solid and hard, and are capable of indefinite extension. The Serpula will 

 bear exposure a half-tide, or rather more, out of water, to the height of spring 

 floods. 



% See Section 4, p. 206, supra. This shell often preserves its colour and nacre 

 in the rock. Capt. Nelson points out how considerable an agent (like the Scarus 

 and Holothuria, noticed by Mr. Darwin) the Conch is in adding to the chalky 

 mud of the West Indian seas, by means of its fsecal pellets, which, when freshly 

 voided, are cylindrical masses made up of numerous minute grains of soft cal- 

 careous matter, together with some organic tissue. 



§ The shell of Turbo pica occurs with its colour and nacre perfect at the sea- 

 level, even at a depth of 50 feet (in borings on high ground). This shell is also 

 found here, as at Bermuda {loc. cit. p. Ill), in the /Eolian rock of the higher 

 grounds, having been carried up by the Hermit Crab. 



II See Section 4, p. 206, supra. Capt. Nelson refers to a like important part 

 played by a species of Pectunculus in forming a thick littoral deposit near Jaffa, 

 in the Levant. 



% The shells of Pupa chrysalis, Ferussac (Specimens 12, 13), occur in the rock 

 at all depths to which the quarries are worked. In the living state this Pupa is 

 to be met with in abundance, crawling about bushes, grass, reeds, &c. Small 

 Helices, now living at Bermuda, are found under analogous circumstances, from the 

 top to the bottom of the Bermuda rock (see Berm. Memoir and specimens). 



** The egg of the AUigator is said to have been found twice in Mr. Burnside's 

 Quarry (see above, p. 207), at a few feet above the sea-level. The Alligator has 

 become extinct in Andros Island in the course of about a century, for Alligators 

 were plentiful in the mangrove swamps of the island in 1726, when Catesby men- 

 tioned them in his work, but none have been seen during the present generation. 

 Although not large, alligators are still numerous in both Crooked Island and 

 Aclins Island. 



