166 CARNEGIE INSTITUTION OF WASHINGTON. 



Of the stony corals growing on the surface of this reef a massive Pontes 

 is the most important single element. On the sand-covered inner portion 

 of the reef this species is the only madreporarian that is at all common. At 

 the reef edge a mushroom-shaped Acropora is abundant near the surface of 

 the water, while at greater depths a Pontes with coarse branches constitutes 

 almost the entire madreporarian fauna. In a few very restricted areas on 

 the reef surface a branching Acropora (like A. muricata) is the dominant 

 element. Fragments of the skeleton of this species are widely dispersed from 

 the place of their origin by the very strong currents and wave-action, so that 

 they make up a characteristic factor in the loose material on the surface of 

 the reef. 



The evidence of the structure of the fringing reef at Utelei, Pago Pago 

 Harbor, as detemiined by the borings, was very incomplete. The thickness 

 of the reef was found to be 121 feet at a point 575 feet from the shore; the 

 character of the material encountered was such that a satisfactory core was 

 obtained from very limited areas only. On the other hand, the contents of 

 the "calyx barrel" (a cylindrical pipe open at the top, of the same diameter 

 and length as the core barrel which extends upward from the upper end of 

 the latter) gave a fairly accurate record of the nature and disposition of the 

 material through which the drill was cutting at any time. Through a greater 

 part of the depth of the boring the material encountered was made up of 

 loosely branching ''coral" with the interstices between the branches filled 

 with calcareous sand which washed out of the bore-hole under the pressure 

 of water necessarily used, so that the coarser material caught in the calyx 

 barrel represented in many instances a minor portion only of the mass actually 

 removed in making the boring. When solid material, such as a massive 

 Porites head, was encountered a continuous core was always obtained. In 

 these few instances the fragmented finer corals were confined in the upper 

 parts of the core barrel and brought to the surface. 



For a depth of about 6 feet from the surface the fringing reef was composed 

 of a solid layer of Lohophytum spicules and Porites skeletons. Immediately 

 below this hard surface crust was a region, some 45 feet in depth, where the 

 sand was so preponderant a factor that the use of a casing was necessitated 

 to prevent the filling of the bore-hole each time the drill was withdrawn. 

 From this depth to the point where the solid substratum of lava rock was 

 encountered, at a depth of 121 feet, the general character of the Umestone 

 was that of a rather loosely branching framework of soUd material, in which 

 was lodged a greater or less amount of coral sand. Although nowhere abun- 

 dant enough to fill up the bore-hole, some loose sand (as yet apparently 

 unchanged chemically) was present, except in the few places where solid coral 

 heads were encountered. 



The material obtained from the boring had in general undergone remark- 

 ably little change in appearance. Many of the madreporarian corals retained 

 the detailed structure of their calices. Indeed, the section of a Cyphastrea 

 head brought up in the core barrel from the depth of 118 feet could not be 

 distinguished, as regards its structural details, from a section through a speci- 

 men on the reef surface to-day. At some levels the fragments of the coarsely 

 branched Porites had undergone a chemical change, in the course of which 

 their substance had become darkened except for a small central axis, roughly 

 a centimeter in diameter, where the original appearance had been retained. 

 The calyces were no longer complete, or sometimes hardly recognizable on 

 this material, and the diameter of the stems had been considerably increased 

 by the addition of extraneous material over their surfaces. Such transformed 



