246 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



mechanical, action of the sea. This irregular honeycombed and cavernous 

 surface extends to the base of the ledge, where it passes into the coarse 

 bank bottom. The base of the ledge may spread somewhat, or it may 

 have been greatly denuded above low-water mark, so as to form a wide 

 base for the seolian pinnacle surmounting it. The interesting feature, 

 however, is to trace the gradual increase of coral and Gorgonian as well 

 as Xullipore and Coralline growth upon these ledges below low-water 

 mark, as we examine them both in deeper water and at a greater distance 

 from the shore. So that when we reach a certain distance from shore 

 where ledges surmounted by seolian pinnacles are rare, and where we 

 find only ledges reaching up to low-water mark, we soon pass into the 

 coral patches, where the coral growth has become so vigorous that it 

 appears at first glance to have been itself the builder of the patches, 

 having so completely buried under its coating the seolian ledge which 

 constitutes its foundation. Unless one has traced the gradual develop- 

 ment of these coral patches from seolian ledges through all their transi- 

 tions, such an interpretation would be most natural. 



The rocks and ledges off Craw Point out to the ship channel, and the 

 rocks and ledges off the north end of Shelly Beach (the Stags), leading 

 to the outer patches as far as the south side of the main ship channel, 

 all tell the same story. We have everywhere the gradual change of an 

 seolian cliff which has become detached from the shore passing into a 

 ledge, and, according to the distance from the shore and depth of water 

 becoming a ledge coated with Millepores, Algse, Corallines, and coral 

 growth, known as " coral heads." The more massive corals and forests 

 of Gorgonians thrive better on the patches near the flats, or on the ledge 

 flats themselves. There is a fine lot of patches to the westward of 

 Mangrove Bay ; they are seolian ledges close to Ireland Island, which 

 gradually pass into coral and Gorgonian patches as one goes to the 

 westward. 



To the west of Mangrove as well as to the west of Daniel Island the 

 patches are in comparatively shallow water, and are surrounded by 

 great stretches of sand, the ledges being more widely separated and 

 cropping out in greater number close to the outer edges of the sand flats. 

 Gorgonians and Millepores flourish mainly on the inner flats, while 

 corals grow, but not in abundance, on the outer ledges. These sand 

 flats with pretty steep slopes seem to be due to the disintegration of 

 great numbers of ledges which must have yielded more readily than 

 ledges elsewhere on the bank to the destructive agency of the sea. An 

 examination of the ledges of the great sound bounded by the Daniel 



