190 DR. a J. HINDE. 



But there is a very striking difference in the proportion of the soHd cores in 

 various parts of the boring, for while in the upper part, from the surface to the depth 

 of 748 feet, the total length of solid rock-core is only 72f feet, or about one-tenth 

 of the distance bored, in the lower part, from 748 feet to the bottom of the boring 

 at 1114|- feet, the length of the solid cores reaches 31 1^- feet, or 85 per cent, of the 

 distance. It may be said that practically the lower third, or 366 feet, of the boring 

 is a continuous core of solid rock ; the upper two-thirds, on the other hand, is mainly 

 of incoherent or lightly cemented rock, with only one-tenth sufficiently consolidated 

 to be brought to the surface as firm core. It is to be noted, moreover, that the rock 

 in the higher part of the boring is to a large extent a limestone, and that in the 

 lower part a dolomite or dolomitic limestone. 



The material from the borino- whether in the form of solid rock-cores or as 

 incoherent granular particles, appears to be entirely of"organic character, and derived 

 from the calcareous skeletons of marine invertebrate animals and calcareous algse. 

 Though there is abundant evidence that siliceous sjoonges were very numerous, for 

 the corals in the cores aie riddled in all directions by their characteristic tunnellings, 

 their spicules have altogether disappeared, and the silica which might have resulted 

 from their solution has not been traced, for there is no indication that any of the 

 corals or other organisms have been replaced by this mineral. Not a trace of pumice 

 or of any other volcmic product has been noticed from any part of the boring. 



The following condensed account of the materials from the boring is intended to 

 give an idea of the general characters of the rock and the organisms in it. The 

 detailed description of the cores appears in the sequel : — 



DejDthfrom Surface infect 0-150. Distance Bored infect 150. 

 Numbers of Cores 1-137. 



The total length of the solid cores in this part of the boring is nearly 26 feet, or 

 about one-sixth of the distance passed through. The rock is a whitish or cream- 

 coloured limestone with patches of a dirty-green tint wherever Heliopora coerulea 

 occurs. It is mainly composed of corals (including Hydrocorallinae and Alcyonaria 

 with the Madreporaria), which under the microscope are seen to retain their minute 

 structures with but little alteration, though they are often rendered very obscure by 

 a secondary deposition in the interior of the corallites of sclerenchyma and crystalline 

 "conchite" or aragonite. The predominant forms belong to Millepora, Heliopora, 

 Pocillopora and Madrepoi-a ; other genera, less numerously represented, are 

 Lobophytuni, Stijlophora, Astrma, Orhicella, Astrwopora, Po^ites and Montipora. 

 A new species of Madrejjora, which'" I have named M. contecta, is very abundant, 

 the cores between 50 and 80 feet largely consisting of it. Heliopora cmrulea is also 

 common, more particularly in the first 40 feet of the boring. 



* See p. 32G. 



