chap. iy. Superficial Calcareozts Beds. 99 



of several hundred feet above the level of the sea. 

 Their position is the same, which sand, if now drifted 

 by the trade-wind, would occupy; and no doubt they 

 thus originated, which explains the equal size and 

 minuteness of the particles, and likewise the entire 

 absence of whole shells, or even of moderately-sized 

 fragments. It is remarkable that at the present day 

 there are no shelly beaches on any part of the coast, 

 whence calcareous dust could be drifted and winnowed ; 

 we must, therefore, look back to a former period when 

 before the land was worn into the present great 

 precipices, a shelving coast, like that of Ascension, 

 was favourable to the accumulation of shelly detritus. 

 Some of the beds of this limestone are between 600 

 and 700 feet above the sea ; but part of this height 

 may possibly be due to an elevation of the land, sub- 

 sequent to the accumulation of the calcareous sand. 



The percolation of rain-water has consolidated parts 

 of these beds into a solid rock, and has formed masses 

 of dark brown, stalagmitic limestone. At the Sugar- 

 Loaf quarry, fragments of rock on the adjoining slopes, 1 

 have been thickly coated by successive fine layers of 

 calcareous matter. It is singular, that many of these 

 pebbles have their entire surfaces coated, without any 

 point of contact having been left uncovered ; hence, 

 these pebbles must have been lifted up by the slow 

 deposition between them of the successive films of car- 

 bonate of lime. Masses of white, finely oolitic rock are 

 attached to the outside of some of these coated pebbles. 



1 In the earthy detritus on several parts of this hill, irregular 

 masses of very impure, crystallised sulphate of lime occur As this 

 substance is now being abundantly deposited by the surf at Ascen- 

 sion, it is possible that these masses may thus have originated ; but 

 if so, it must have been at a period when the land stood at a much 

 lower level. This earthy selenite is now found at a height of 

 between 600 and 700 feet. 



