210 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



" Atolls" ; whilst such as Silver Bank, Mouchoir, and Navidad are 

 little more than sand-banks. 



6. Flora and Fauna as contributing agents. — The increase of land 

 in the Bahamas, as elsewhere, is in a considerable degree due to the 

 agency of Plants, either as mechanical or secreting agents. Drifted 

 sea-weed sometimes affords a temporary bond for the sand, in which 

 mangroves*, creepers, grasses, &c.-|' form further centres of aggre- 

 gation, their rootlets binding the sand together, and their foliage 

 affording a protection from the wind. The submarine plants, such 

 as Mangrove roots, Turtle-grass, &c., act in an analogous manner, 

 whilst the calciferous plants (Corallince, &c.X) not only aid by means 

 of their roots to consohdate the mud and sand, but supply a vast 

 amount of calcareous and carbonaceous material from their owti sub- 

 stance. The marshy lands, that are gradually taking the place of 

 the creeks and brackish lakes, abound with, and may be said at 

 some points to consist largely of, a highly calciferous moss-like 

 Conferva §, which, in concert with mangrove roots, grasses, and other 



* The Mangrove-swamps of the low moist lands of the tropics are well known. 

 In the swampy clay and sand of the Florida coast the Mangroves form dense 

 jungles, from five to twenty miles broad, and running up the creeks and inlets; 

 and parts of the AVest Indian Islands (the N.W. inshore coast of Cuba, for exam- 

 ple) are extensively occupied with them. The Mangi-ove {Rhizophora) seldom 

 grows more than 15 feet in height; the strength and durability of its timber are 

 very great ; and, from its development of roots, and its amphibious habit, it is an 

 important agent in the conversion of swamps and littoral tracts into dry land. 

 There are many species ; but the most common in the Bahamas are the Yellow 

 and the White Mangroves. The Yellow Mangrove sends out horizontal roots 

 inland, and into the water it throws down numerous vertical radicles or branch- 

 like roots (to which a variety of living things soon become fixed) ; it also throws 

 off bud-plants, which, di-opping into the water, float until they attain a mud-bank 

 or rock-head, or other congenial point for fixture. The White Mangrove throws 

 down no pendants, but on every quarter it throws off roots which penetrate the 

 mud horizontally about 6 or 8 inches under the surface, and send up suckers at 

 every 3 or 4 inches of their course. Thus each species, by the multiplication of 

 roots and stems, becomes an effective agent in the retention and increase of soil, 

 and frequently both combine in their work of encroachment on the water and 

 formation of land, pushing across creeks and inlets ; as is well seen along the 

 N.E. shore of Cunningham Lake, from the ridge between it and the Lake Killarney. 



One of the best instances of the formation of land that I have ever seen, says 

 Capt. Nelson, was a beautiful little bouquet or wreath of Spongilla and Acetabu- 

 laria floating in the water from the end of a Mangrove dactyle, in the rear of 

 which, for a foot or two along the shore, was a loose floating mass of similar, but 

 chiefly dead, material ; and in the rear of this again was a compact mass of vege- 

 table soil, consisting of the same material decomposed, and strong enough to bear 

 one's weight tolerably well. 



t Ipomsea orbicularis, Artemisia maritima, Rhipsalis, Inula, Graminese (repent 

 and fibrous at the root-joints), many species, Coccoloba uvifera, Chrysobalanus 

 icacos, Statice, &c. 



% CoralUna. Udotea. Callithamnium. 



Nesea. Acetabularia. Ptilota. 



Jania. Myriapora. Polysiphonia. 



Amphirhoe. Nullipora. Grifiithsia. 



Halimeda. Conferva. Sphaicellaria, &c. 



§ Capt. Nelson describes this moss as a spongy mass of laterally aggregated 

 and xa\\c\i-mte.xvio\en fasciculi of tubes, perhaps -itro" i" diameter. On dissolving 

 the chalk secreted by, and coating these tubes, the latter remain as transparent 



