310 PKOCEEDINGS OF THE ACAUEIMY OF [1890. 



existed, but an additional structure, in the form of a stone wall much 

 resembling apiece of masonry, has been superadded as the result of 

 a single heavy storm, the hurricane of Sep. 8, 1888. 



All of the reefs receive a breaking water, caused by theup-throw 

 of disjointed boulders, and the heavier break is on the lee or shore- 

 side, where the rock-masses have accunnilated in greatest abund- 

 ance. The long rolling surf, occurring in scattered patches over the 

 blue waters, is a beautiful sight of the harbor. The more or less 

 regularly oval shape of the reefs recalls the atoll-form, and a hasty 

 examination of the region might lead to the assumption that the 

 islets are true atolls. But this is not the case. It is true that a 

 circular or elliptical form distinguishes some of the reefs, and that 

 in others a patch of dry land is found surrounded by a more or less 

 continuous ring of coral and a separating channel of water ; but the 

 conditions as they are presented are not those of true atolls. The 

 form is that of almost any bank that rises either out of the water or 

 close to its surface — the tendency of water-action being to round off 

 the obstructions that may interpose themselves — and' the included 

 water is only a shallow pan, and not the distinctive lagoon of an 

 atoll. The depth of water over the reefs generally is inconsiderable, 

 from one and a half to perhaps six or seven feet, and some of the 

 reefs are almost laid dry in low-water. This was the condition of 

 the Gallega Reef when we finally left the harbor of Vera Cruz. 

 The actual " ring" of the reefs, where it exists at all, is thus neces- 

 sarily insignificant, and it is largely due to the mechanical action of 

 water ; in some parts it may arise from accelerated organic growth, 

 but on this point I could not satisfy my mind. Be this as it may, 

 the lagoon is certainly neither a lagoon of solution nor one of subsi- 

 dence. 



In the case of some of the reefs, as Gallega and Galleguilla — in- 

 deed, I am not sure if this is not true of most of the reefs — the 

 greatest development of coral growth seems to be on the lee- or shore- 

 side, or opposite to that which is generally supposed to receive the 

 greatest supply of organic particles. The brain-corals and madre- 

 pores are there developed in immense profusion, although barren 

 areas of sand here and there project themselves into the living 

 mass. The scarcity of animal life on these sand tongues or patches 

 is very remarkable ; for long reaches we saw absolutely nothing in 

 the shape of animal existence, while at other points there may have 

 been a few shells (Triton, 3Iurex) thinly scattered about. We 



