238 bulletin: museum of comparative zoology. 



masses of Algse and of coralline Algse, and Nullipores, with compara- 

 tively few massive corals. As far as I am aware, this broken ground 

 does not extend on the northern sea face of the ledges as far out as off 

 the southern ledges, where the fishermen report its existence to a depth 

 of from sixteen to seventeen fatlioms. 



The ledge patclies rise in steps from the coralline bottom depths, 

 much as they fall in successive ledges off the shore clifi's. As we ap- 

 proach the bank edge of the flats, the ledges become smaller, the depth 

 of water increases, and the sand spaces between the patches increase, 

 often forming long tongues extending into the main body of the ledges 

 of the flats. Many of the ledges near the edge come quite close to 

 the surface, and a great number are awash at low -water, although the 

 depth of water between them is greater than at the point we might call 

 the crest of the ledges. The nearer we come to the breakers, the greater 

 becomes the wear of the sea slopes of the ledges, so that in many 

 places their slope is qtiite abrupt, from two or three to five fathoms, and 

 a somewhat gentler slope extends from that point seaward to form the 

 broken ground. 



The high seolian cliffs of the south shore probably extended to the 

 outlying reef, which is itself only a series of ledges running parallel to 

 the coast, the crests of which are bare at low water. On these and the 

 inner irregular flat ledges which dot the bottom over greater or smaller 

 areas between the outer ledges and the shore grow corals and Gorgo- 

 nians, — a comparatively thin veneer, which supplies, when dead or 

 beaten off by the surf, a part of the material which goes to form the 

 sandy beaches of the south shore, — though by far the greater mass of 

 the material is derived from the disintegration of the ledges themselves. 

 So that the submarine remnants of the ancient seolian hills supply the 

 material which to-day creeps over their faces and finds its way inland, 

 much as they in their own time must have crept over the lowland exist- 

 ing within the limits of the proto-Bermudian coral reef. 



From the observations I have thus far made, it seems to me as if 

 the corals now growing at the Bermudas had, as at the Bahamas, 

 played a very unimportant part in building up the mass of the reefs. 

 It is true that some of the flats are largely formed of coralline coral 

 and ajolian sand, derived in part from the coral patches which line 

 their faces. But as yet no islands or islets have been formed by their 

 disintegration, showing that the coral growth is not rapid ; and al- 

 though In some of the patches along the inner edges of the flats and 

 on some of the connecting patches the corals have attained sufficient 



