NELSON ON THE BAHAMAS. 209 



but announced that all tlie varieties gave off ammonia, whether 

 retaining organic texture or not. The author thinks it not unlikely 

 that the "red earth," even in the case of the five strata in Ireland 

 Island, has been largely derived from Bats inhabiting once-existing 

 caverns ; at the same time, he considers it probable that Birds*, 

 their droppings supplying a sort of guano, have also assisted in the 

 formation of this deposit. 



The occurrence of pumice floated ashore at Watling Island, and 

 elsewhere in the Bahamas (as also at Bermuda), is briefly noticed. 



5. Increase and Decrease of Land. — The present relation of 

 destruction and replacement, as far as the formation of rock above 

 the sea level is concerned, would imply that it is on the wane, and that 

 the accumulation of the once-existing land, of which we have such 

 such extensive wrecks, belonged to another set of operations. But 

 although we do not see the formation of rock in progress above the 

 sea, as at Elbow Bay, Bermudaf, but only the preparation of the 

 materials, yet consolidation is doubtlessly going on below the sea- 

 level. 



That however the original constructive power by which the hills 

 were accumulated is still perceptible and can be measured, may be 

 seen, though on a small scale, at Lyford Cay (New Providence). 

 This was an island in 1 775, with at times 9 feet depth of water in 

 the channel, which was filled up by 1804, and is now replaced by a 

 sandy isthmus about 10 feet high, covered with creepers, grasses, 

 bush, and palmettoes. Other local evidences of the increase of land 

 are alluded to. 



The exposed long linear coral-reefs are peculiarly open to de- 

 struction, and the J^olian formations carry an element of destruction 

 in their dome-shaped structure, which on the sea-coast is easily 

 worked into vaults and caverns. 



As related to the construction and destruction of land, Capt. 

 Nelson notices in detail the more or less entire belts of rock, which 

 were evidently aggregated at first along, together with, and over 

 coral stripes, at successive epochs, and are all more or less parallel to 

 existing coast-lines, or to the lines of hills in the interior. One of the 

 most complete and extensive examples of these is at the north-east of 

 the Great Bahama Bank, where it is exposed to the ocean, and where it 

 is in a measure fenced in by a quadruple barrier of four lines en echellon, 

 each line having apparently once been much wider than at present. 

 The barrier is in various ways carried round the whole of the east, 

 north, and north-west sides of the Great Bahama Bank, generally 

 speaking where most exposed. Cay Sal Bank is likewise contoured 

 by islets and rocks round the eastern, northern, and half of the 

 western margin. The Little Bahama Bank, Crooked Island, Caicos, 

 and Watling Island afford interesting studies of more or less perfect 



* Birds are locally very abundant. On Water Cay, near Cay Sal Liglitliouse, 

 sea-birds nestle over the whole surface of the island, under every little rock -head 

 that can afford shelter. See also the notice of the Pim-li-co, and the occurrence 

 of bird bones in the red earth, Bermuda Memoir, loc. cit. p. 113. 



t Bermuda Memoir, loc. cit. p. 110. 



