AGASSIZ : BERMUDAS. 225 



Darwin's suggestion that the fringing reef on the south side of the 

 Bermudas is evidence of recent elevation, does not, in view of the fact 

 that the reef is made up of seolian ledges, need any. discussion. Nor is 

 the reason given hy Dana regarding the cause of the great difference 

 in the amount of dry land on the north and south side of the atoll a 

 satisfactory one, if the ledges are aeolian ledges, which were the first to 

 disappear after subsidence began. I am inclined /to look upon the 

 present state of things as due to the former existence of lower aeolian 

 hills on the northern edge of the islands ; * but his views would apply 

 for proto-Bermudian times. 



My observations lead me to look upon the beach rock of the Bermudas 

 as consisting mainly of the larger and heavier aeolian materials, which 

 either have not been carried so far or blown to so great a height as the 

 lighter aeolian sand. The effect of the intermittent submersion of the 

 aeolian rocks exposed at low-water mark seems to be to cement the par- 

 ticles on the exposed lines of the knife-edged strata by a process very 

 similar to that going on in all the deep road cuts on the islands. By it 

 all traces of stratification are gradually lost, and an upper crust running 

 over the exposed surface is formed irrespective of the aeolian layers. 

 Thus a belt of comparatively hard rock is formed, covered with a crust 

 ringing to the hammer, which at first sight appears to be unconformable 

 with the aeolian strata. A closer examination invariably reveals at no 

 great distance traces of the continuation of the aeolian stratification, 

 which continue plainly visible to high-water mark, to points below it, 

 and at intermediate heights. Where the sea breaks violently against a 

 vertical cliff, this cementing effect, accompanied by the disappearance of 

 the evidence of stratification, can be traced in some cases well above 

 high-water mark, where it gradually passes into the region honeycombed 

 and pitted by the action of the rains. Such parts of the rocks cannot 

 be distinguished from the base rock, and they have all its characteristics 

 except that the cementation is not quite so complete (Plates XV.-XVII. 

 and XXV 1 1 1.). 



Here and there along the beaches beach rock is forming, as in some 

 parts of Great Turtle Bay, of the shore south of Whale Bay, in Whale 

 Bay itself, and between short projecting headlands where the debris from 

 the outer and inner ledges accumulates in greater quantity. This beach 



1 It seems somewhat hazardous to attempt, as Rice has done, to correlate the 

 movements of elevation and subsidence of what prohahlv is a volcanic cone — of 

 which lie has, as he thinks, found evidence — with those of the American conti- 

 nent. (Bull. Nat. Mus., No. 25, p 18 ) 



vol xwr. — wo. 2. 15 



