204 



NA TURE 



[December 27, 1894 



Bank,' expresses the general result of this piece of 

 research verj' clearly and concisely, showing that its 

 value is fully recognised by the' authorities at the 

 Admiralty. 



The Macclesfield Bank is a shallow patch, rising 

 abruptly from deep water in the middle of the China 

 Sea, crossed by the parallel of i6 N. and frequently 

 passed by vessels. It is of an oval shape, about So miles 

 long and 30 wide, with a general depth of about 40 

 fathoms. Reports having been made of very shallow 

 water on the edge of this bank, forming a possible danger 

 to shipping, a complete sur\-ey was resolved upon, and as 

 preliminary soundings had shown indications of a raised 

 rim, instructions were given to pay special attention to 

 the animal life upon what might turn out to be an atoll 

 entirely beneath the surface of the sea. Half of the reef 

 was surveyed by Captain Moore in the Penguin in 1S92, 

 and collections made by means of dredges and divers, 

 under the superintendence of Mr. Bassett-Smith, several 

 tons of specimens being subsequently despatched to the 

 Natural Histor)- Museum for full study. The remainder 

 of the bank was examined in 1S93 by Captain Field in 

 the Egfri.i, to which ship Mr. Bassett-.Smith had ex- 

 changed in order to continue his work, and the result 

 is such an investigation into the biological conditions of 

 a submerged coral reef in mid-ocean as has never been 

 made before. 



The whole circumference of the bank rises as a 

 ring of coral to within from 9 to 15 fathoms of the 

 surface, being broken here and there by wide gaps of 

 greater depth, but never so deep as the central depres- 

 sion, which varied generally from 40 to 4S fathoms. The 

 minimum depth on the rim was 6* fathoms, and an iso- 

 lated shoal rising from the centre of the inner depression 

 reached to within 5 fathoms of the surface. 



The uniformity of the depth appears to Captain 

 "Wharton to be a strong argument against any move- 

 ment of the bottom since the period when the atoll form 

 was assumed ; and he shows that the simple growth of 

 coral on the rim will in time suffice to produce a perfect 

 ring-shaped coral island without the aid of subsidence or 

 upheaval. It appears, in fact, that here is an atoll in 

 course of formation on a foundation sufficiently near the 

 surface to allow coral to grow. Such a foundation 

 Darwin admitted might allow a coral island to form 

 without subsidence, and the recently discovered abun- 

 dance of similar elevations in the tropical oceans is one 

 of the main arguments for Murray's general theory of 

 coral growth. 



Mr. Hassett-Smith's first day's dredging convinced 

 him that the Macclesfield Bank was by no means a 

 " drowned atoll," but on the contrary that it was very 

 much alive. The basis of the bank appeared certainly 

 to be dead coral-rock, or in many places a calcareous 

 rock composed of the consolidated vegetable organisms 

 which seemed most common between the depths of 20 

 and 50 fathoms. Upon this ground corals grew in 

 great patches, and other forms of life were very abundant, 

 especia\ly echinoderms, molluscs, crustaceans, and anne- 

 lids ; many very striking cases of mimetic resemblances 

 were observed amongst them. Altogether forty-one 

 genera of corals were dredged, excluding .alcyonarian 

 and hydroid corals : twenty-nine genera occurred between 

 25 and 35 fathoms, and tweniy-seven genera in deeper 

 water. It appears that reef-building corals can thrive at 

 depths as great as 50 fathoms in the conditions of the 

 Macclesfield Bank, where the water is very clear and 

 warm. Concerning the genera represented, Mr. Bassett- 

 Smith says : — 



M.. 

 A. 

 I- 

 P 



Reporl on Ihe RcibIk of Drcdiinza obtained on the 



in H M S r.lr •; '. r„m,,.,-„lr, \V IT. M..or.-, R.N., 



April 

 Her 



NO. 1313. VOL. 51] 



" The most universally distributed were Seriatopora, 

 Pavonia (especially a variety of forms very nearly allied 

 to Mycedium ekgans of Milne Edwards), Lcploscris 

 Montipora, and Styloplwr,^ Ciintheii, at all depths, but 

 the sections ' Madreporaria Fungida' and 'Perforata' 

 are undoubtedly most frequently met with in depths over 

 20 fathoms, and continued down to between 40 and 50 

 fathoms : the corallum being almost always light and 

 delicate. Agavicia, Phyllaslraa, Pacliyseris, Turbinaria, 

 and Liptoseris, in cups of varying size, from two inches to 

 twenty inches across ; Orypori, Pavonia, Hydrophora, 

 Scaphophytlia, and Montipora, in leaf-like expansions ; 

 Cyphastraa, Galaxca, Turbinaria and Montipora, in 

 encrusting growths ; or in branching forms, as Seria- 

 topora, Afussa, Madrepora, Psammocora, Napopora, 

 Anacropora, Alveopora, and Rhodarica ; the most 

 massive forms found in deep water being Pocillopora, 

 Stylophora and Mussa. On the sandy bottom of the 

 lagoon, and near the rim, the corals that seemed to 

 thrive best were small branching forms of Psammocora, 

 and Anacropora : delicate frond-bearing clumps of 

 Pavonia; Lcploscris cups, thick but light spreading 

 branches of Alveopora, Montipora ; and many simple 

 corals as Cycloseris, Fungia, &c. Small fragments of 

 more massive Astrcea were brought up three times from 

 deep water, twice from 30 to 40 tathoms, and once from 

 40 to 50 fathoms." 



There was a strong current over the rim, even in calm 

 weather, and the surface water, the temperature of 

 which was sometimes as high as 88° F., swarmed with 

 Plankton. 



In addition to the chart of the bank showing its un- 

 mistakable atoll form, the blue-book contains two 

 sections of the outer slope on a natural scale. The 

 angles varied somewhat on different sides. On the 

 north the slope was gradual, the 100 fathom line being 

 one mile distant from the 20-fathom line, while 200 

 fathoms was only found ten miles farther out, beyond 

 which the slope became more rapid to iioo fathoms six 

 miles beyond. On the east there was a much steeper 

 slope, the loo-fathom soundings being found half a mile 

 from the 20-fathom and 300 at the distance of a mile, 

 while fifteen miles away the depth was 2100 fathoms. 

 The wall-like spring of the bank from the ocean floor is 

 still more striking on the south, where depths of 150 

 fathoms occur half a mile from the edge of the bank, 30C5 

 fathoms at the distance of one mile, and. the oceanic 

 depth of 1100 fathoms, only 3J miles away, giving the 

 remarkably high average slope of i in 3. The shoal at 

 the north end of the future island is attributed to the 

 strong current from the south-west sweeping the debris 

 over the edge of the oceanic hill into the deep beyond. 



The observations fully confirm Dr. Murray's preference 

 for the term " organic " rather than " coral " as applied 

 to the origin of atolls, for a very large part of the grow- 

 ing rock was shown to be due to calcareous alg.x, to 

 corals other than reef builders, and to the accumulation 

 of the calcareous remains of Crustacea, mollusca and 

 annelids. Mr. Bassett-Smith suggests that the crust of 

 alga: prevents the dissolved carbonic acid of the sea-water 

 from touching the dead coral rock below, while the 

 action of the growing alga; might decompose the 

 carbonic anhydride. This we are inclined to doubt, as 

 the decaying organisms would seem likely to produce 

 far more carbonic acid than could be disposed of by 

 the very feeble daylight which reaches depths approaching 

 40 fathoms ; and from the continual dredging of '' rotten 

 rock " in the central depression, we feel inclined to think 

 that active life and rock-growth are taking place there 

 only in restricted patches. The observations seem to 

 leave no doubt that the atoll is growing towards maturity 

 and the air, not declining from a past existence as an 

 island. 



Huc.H Robert Mill. 



