SAL T KE Y BA NK. 1 8 1 



wall, broken down here and there to the water's edge. The 

 whole ridge is composed of the finest oolite, pretty regularly 

 stratified, but here and there like torrential deposits ; the strati- 

 fication is more distinctly visible where the rocks have been 

 weathered at the surface' into those rugged and furrowed slopes 

 familiarly known as ' karren ' in Switzerland. It is plain that 

 we have here the same formation as on Salt Key, only older, 

 with more thoroughly cemented materials. The uniformity in 

 the minute grains of the oolites leaves no doubt that the sand 

 must have been blown up by the wind, and accumulated in the 

 form of high dunes before it became consolidated. The 

 general aspect of Doubled-Headed Shot Key is very different 

 from that of Salt Key. The whole surface is barren — not a 

 tree, hardly a shrub, and the scantiest creeping vegetation. 

 The rock is very hard, ringing under the hammer, and reminds 

 one of the bald summits of the Jura, such as Tete-de-Rang, 

 near La-Chaux-de-Fond. It is evident that what is beginning 

 on Salt Key has here been not only completed, but is under- 

 going extensive disintegration in Double-Headed Shot Key, 

 both by the action of atmospheric agents over the surface and 

 by the action of tides and winds against the base of the Key. 

 " Among these older oolitic deposits, forming the main 

 range of Orange Key, and of Double-Headed Shot Key, we 

 recognize formations of more recent date, occupying the 

 cavities of ancient pot-holes, which have been gradually filled 

 with materials identical with those of the older deposits. The 

 pot-holes themselves show nothing very peculiar ; there are 

 many such upon these Keys — some large ones many yards in 

 diameter, and others quite small — evidently formed by the 

 wearing action of loose pieces of harder coral rocks thrown 

 upon the Key by great waves, and only occasionally set in 

 motion by the waters dashing over the Keys during heavy 

 storms. The pot-holes nearest the water's edge are the most 

 recent, and are mostly clean excavations, either entirely empty 

 or containing sand and limestone pebbles lying loose at the 

 bottom of the holes. Some of these excavations are circular ; 

 others oblong ; still others have the form of winding caves 



