Feb. 23, 1888] 



NA TURE 



395 



atoll is not new. Darwin says, " A bank at the proper 

 depth beneath the surface would give rise to a reef which 

 could not be distinguished from an atoll formed during 

 subsidence." Murray says, " Very early in the history of 

 such an atoll, and while yet several fathoms submerged, 

 the corals situated in the central parts would be placed at 

 a disadvantage." It does not, however, appear to have 

 been contemplated that the inclosed lagoon would, under 

 any circumstances, without some further agency than the 

 simple growth of the rim, be so deep as it appears to 

 me, from the cases above cited, that it can be ; nor, so far 

 as I can find, have any such instances been before re- 

 marked. 



Darwin notices the case of the Chagos Bank, but, on 

 the authority of Captain Moresby, he states that the rim 

 is dead, and concludes that life was killed by subsidence, 

 and he apparently also infers that it will not grow to the 

 surface. 



I can find no fresh evidence on this particular reef, but 

 for some of the banks in the China Sea I have the in- 

 dependent testimony of two of the officers employed in 

 their survey, Stafif-Commanders Tizard and Petley, R.N., 

 that the coral growth is most luxuriant. 



Touching for a moment on the point of the formation 

 of banks at a proper distance below the surface ; the in- 

 vestigation of banks in the Atlantic, recently described by 

 Mr. J. Buchanan, shows that banks with almost wall- 

 like slopes are growing up by the accumulation of 

 organisms. 



Turning to barrier reefs, similar instances can be 

 found. Off the coast of the island of Palawan, a shallow 

 rim is forming on the edge of the bank which stretches 

 from the island to a distance varying from 15 to 30 

 miles, having a general depth on it of 40 fathoms. The 

 length of the rim is 250 miles, and it consists of streaks 

 and patches of coral with from 4 to 30 fathoms on them. 



On the south of the eastern end of New Guinea, a 

 formation, known to navigators as the sunken barrier, lines 

 the edge of a bank similar to the above, and is of precisely 

 the same character. Its length is 140 miles, and the 

 depth between it and the land varies from 30 to 60 

 fathoms. 



Dr. Guppy has recently pointed out some smaller 

 instances of the same tendency in the Solomon Islands, 

 and has made some remarks on the formation of barrier 

 reefs in the same sense as my suggestions. I am not 

 therefore advancing anything novel, but simply pointing 

 out evidence which tends to show that the principle may 

 be carried further than has hitherto been supposed. 



Looking now at the fringing class, how comes it that so 

 many wide reefs of this character exist, which, if Mr. 

 Murray's contention be correct, should surely show more 

 signs of the formation of a lagoon channel than they do .'' 

 Take the case of Rodriguez, in the Indian Ocean, with 

 which I am personally intimately acquainted. Here a 

 fringing reef surrounds the western sides of the island for 

 a width of 4^ miles. There are narrow channels it is 

 true, but so shallow that in many places boats cannot pass 

 at low water. The island is situated in the heart of the 

 strong trade winds, and the reefs are exposed to a heavy 

 sea, which, with a rise of tide of nearly 6 feet, gives every 

 facility for scour and rapid change of water. 



I am not disputing the fact that calcareous dead 

 organisms are dissolved by carbonic acid. I am no 

 chemist, and moreover the C7/i3;//^/74'"^r observations amply 

 prove it, but I would ask Mr. Murray if there is not a 

 great difference between the position of small shells falling 

 in water which completely surrounds them whilst they 

 are constantly coming in contact with fresh particles of it, 

 and of the more or less solid mass of a coral reef, which 

 can only be attacked on its upper side to advantage, and 

 where the resultant fine mud covers and protects the re- 

 maining rock, especially in the case of lagoon channels, 

 when the bottom is partly composed of detritus from the land. 



At the bottom of a lagoon of any depth, moreover, the 

 motion of the water must often be comparatively slight, 

 and the action consequently extremely slow. 



The rotten state of the surface of every coral reef awash 

 with the water shows that this disintegration is going on, 

 but the fact that for large areas it remains awash, and must 

 have so remained for ages, seems to me to point to the 

 supposition that the removal of matter is too insignificant 

 to account for the formation of deep lagoon channels in 

 this manner, though doubtless it may explain the shallow 

 pools and creeks found in all fringing reefs. 



I have addressed myself solely to one point in this 

 many-sided question, but I may add my opinion that, 

 before any explanation which will fully account for the 

 almost infinite variety of coral formations, can be given, 

 much more knowledge of details of the complex conditions 

 under which they may grow is required. 



Certain knowledge of the depths at which different 

 corals and other lime-secreting animals live under vary- 

 ing circumstances ; of the amount of food carried in the 

 different strata and in different waters ; of the effect of 

 the velocity of the currents that bring the food to the 

 banks ; and more accurate surveys on large scales, 

 especially of the shapes and contours of coral reefs, and 

 of their composition, are all wanting. These details must 

 greatly affect coral growth, and the results must greatly 

 vary. On the other hand, similar results may be brought 

 about by different causes. 



It may surprise some to learn how little in the prelimin- 

 ary matter of surveys alone has been done in the principal 

 coral-reef regions, especially in the Pacific, which is 

 generally quoted ; and consequently how very inexact our 

 knowledge is of the depth both inside and outside of the 

 majority of atolls in the world, and also of the state of 

 the bottom of the sea, on which it is very possible that 

 many elevations may be found in the condition of those 

 to which I have called attention. 



In the Pacific the vast majority of islands have been 

 merely sketched without a single sounding having been 

 taken, either inside or outside lagoons. 



I append a few statistics relating to the larger coral 

 groups to show our position in this respect ; merely re- 

 marking that the waters of the Fiji and the Society Islands 

 are the only ones which can be said to be in any sense 

 surveyed. 



No. of Islands. No. surveyed. 



PauT.otu Islands ... 74 ... I partially. 



THE AKKAS, A PYGMY RACE FROf 

 CENTRAL AFRICA. 



AT the last meeting of the Anthropological Institute, 

 Prof Flower gave a description of two skeletons 

 of Akkas, lately obtained in the Monbuttu country, 

 Central Africa, by Emin Pasha, and by him presented 

 to the British Museum. Since this diminutive tribe was 

 discovered by Schweinfurth in 1870, they have received 

 considerable attention from various travellers and anthro- 

 pologists, and general descriptions and measurements of 

 several living individuals have been published, but no 

 account of their osteological characters has been given, 

 and no specimens have been submitted to careful 

 anatomical examination. The two skeletons are those 

 of fully adult people, a male and a female, but un- 

 fortunately neither is quite complete. The evidence 

 they afford entirely corroborates the view, previously 

 derived from external measurements, that the Akkas 



