120 TRANSACTIONS OF THE [jAN. 18, 



subsidence began, but the accumulation was verj- slow and with- 

 in narrow limits for a long time. The thin deposit in the Ireland 

 island excavation is crowded with helices; so everywhere else, 

 helices abound in the first two to six feet above the limestone or 

 the intermediate deposit, whereas they are comparatively' rare 

 higher up in the sandstone. And this condition in the lower 

 portion continued even as late as the Devonshire ba}^ deposit, 

 when the subsidence had reached its extreme limit. Marine de- 

 posits ceased when subsidence had carried the land to approxi- 

 mately the present level, and the Devonshire bay, Stocks point 

 deposits mark the lowest line to which the land sank. Rapid 

 accumulation of the sandstone did not begin until after this sub- 

 sidence ceased, for the thin helix-\)Q(\ rests on the highest of 

 these marine deposits, and is continuous thence over the lime- 

 stone bosses inland. 



This later deposit covered the whole land area ; it is the rock 

 on which corals grow in Castle harbor, the lagoon and other 

 bodies of water; it covers islands off the south shore, in the 

 lagoon, within the " hook " and forms the pinnacles of North 

 Rock, the only portion of the Ledge Flats land now above water. 



Any depressions existing on the land, when this rapid accumu- 

 lation began, must have become filled up with sandstone. The 

 altitude of some hills on the northerly shores leads to the convic- 

 tion that the sandstone must have been sufficient to fill up any 

 depressions existing in the lagoon area or in the great reef. 

 Gibbs hill near the south shore is 250 feet, while near the north 

 shore beyond Hamilton harbor are Mt. Langton, 168 feet and 

 Prospect hill, 222 feet high ; Scaurs hill near the south shore is 

 260 feet, while near the north shore bej'ond Harrington sound a 

 hill rises to 180 feet; Paynter's hill at southeast of Castle har- 

 bor is 204 feet, while St. David's Head on northerly side is 

 127 feet and Fort George on St. George is 178 feet. These are 

 all sandstone hills. 



The three hundred feet, more or less, of the sandstone, which 

 remains for study is only part of the original deposit, for surface 

 erosion must have removed not a little of it, so that the original 

 dunes may have been as magnificent as those of Turkestan. 

 Whence this vast accumulation could come is hard to determine. 

 Rice finds the explanation in elevation, which appears to be the 

 explanation accepted by Heilprin ; while Agassiz finds the neces- 

 sary conditions during subsidence when new portions of the land 

 would be brought within reach of the waves. It must be con- 

 fessed that in accepting either of the explanations one accepts 

 something that needs much amendment, constant addition or 

 subtraction, yet there is no positive middle ground to be taken. 



