314 J. STANLEY GARDINER. 



PAGE 



Section V. The Action of Boring and Sand-feeding Organisms 333 



I. General — Importance for Solution — Action and Effects of Organisms — Deposits 

 of Coral Muds and Sands — II. Boring Organisms— Sponges and Algae — 

 Lithodomus — Sipunculoidea— Polychaeta (great Importance of, Distribution, 

 Note by Prof. Wlntosh)—Lithotrya — Other Forms— III. Sand-feeding Or- 

 ganisms — General — Holothurians (Distribution, Holothuria maculata, Observa- 

 tions on Stichopus chloronotus and Holothuria atra) — Echinids — Abundance of 

 Ftychodera — SipuMculns — Polychaeta. 



Section VI. Beach Sandstone ............ 342 



Conditions of Formation — Protected Beaches — Presence of Silica or Organic Matter 

 — Constitution — Mode of Occurrence — Development — Undermining — Terraces — 

 Erosion of Land — Justifiable Deductions. 



(To be continued.) 



APPENDIX A. 

 Section I. The Seaward Slopes of Atoll Reefs. 



I HAVE already repeatedly referred to the subject-matter of this Section in the previous 

 Chapters of this Report (pp. 38—44 and 177). I have also therein stated that the reef is 

 growing up everywhere outside the atolls (p. 49) without really attempting to show or prove 

 that such is the case — to a certain extent assuming the upgrowth to be a matter beyond 

 dispute. I have done so for two reasons, (1) to simplify the subject-matter in the previous 

 chapters, and (2) because I felt that without a special, more detailed, yet somewhat 

 generalised account of the whole seaward slope it would be impossible to satisfactorily show 

 the evidence on which the above deduction was based. In the following pages I have 

 attempted such a description, but I freely recognise that our investigations of the seaward 

 slope in the Maldives were scarcely sufficiently complete to really warrant my doing so. 



The outer or seaward slope of any bank in the Maldives opposite its encircling surface 

 reefs is usually covered with a dense growth of corals and other organisms down to the 

 depth at which the steep commences. The edge of the reef, although broken up by fissures 

 extending into it for some distance, is usually fairly well-defined. Beyond it the seaward 

 slope, as deep as the eye can see, i.e. to about 15 fathoms, is generally much broken up 

 by masses and buttresses of the rock, the latter extending out at right angles from the reef, 

 as well as by large colonies of corals. At least the latter evidently continue further out 

 to 25 or 30 fethoms, the lead down to these depths often resting for a moment and then 

 dropping off again for an additional 2 or 3 fathoms. The bottom, however, so far as the 

 actual masses of the reef rock are concerned, actually becomes more level with each ad- 

 ditional fathom of depth, until beyond 30 fathoms the reef-platform in the slope of its 

 foundation rock is almost or quite level. 



