124 



NA TURE 



IDec. 6, 1883 



in sliape." Looking again at the ilIu^ll■ation, for "rows "he 

 finds that the liones which seen to be arranged in raws are 

 tliosp which he may afterwards learn to be the metacarpals and 

 ]ihalnnges. Supposing, however, that he guesses the carpu^ 

 righllv, which of its bones is semi-lunar or crescentic in shape? 

 I think if the picture were put before any ordinary observer, 

 told 1 ) point out a crescentic bone, he would sehct the scaphoid. 

 Theie is, thinl:s the student, still a clue left, for the semidunar 

 "occupies the centre of the first row." But the first row con- 

 tains y.'/;;- bones ; at least he has read that " the eight b^nes are 

 clustered together so as to form two groups," and he is not told 

 that these groups are not the "rows" afterwards mentioned. 

 He give-^ it up, and reads the other bjnes to barn them and find 

 the S'?nii-lunar by t' e exhaustive process. The guide he finds to 

 the cuneiform bone is that it is " on the ulnar side of the semi- 

 lunar," which he has perhaps failed to guess rightly, and articu- 

 lates with certain other bones, which are to be afterwards 

 described, and are unknown to him ; and so on. 



The mode of progression is like that I made once in Ireland, 

 when on asking a peasant my way I was told to take the last 

 turni.'g before coming to the next milestone. There were a 

 good many s'eps to retrace after findino; the next milestone. 



I have no doubt at all of the mjral infiuenceof Mr. Marshall's 

 plan if the student peyseveres in using his book; he will have 

 exercised patience, attention, command of temper, and careful 

 criticism of words, but I do not think his anatomical will equal 

 his moral gain. 



The ])rocess described above simply distracts the student's 

 attention from the form of what he is studying. Would Mr. 

 Marshall wish the Map of England taught in the same manner — 

 no names or references given to the counties, and Hampshire to 

 be recognised because it is in the last row and adjoins certain 

 other counties, which in their turn adjoin it ? 



Art Student 



Barytes from Chirbury 



I HAVE to thank Mr. Woodward for pointing out that the 

 plane {412) has been establi-hed for barytes. It was fir.-t given 

 by Helmhacker (Denksch. der K. Akad. dcr Wiss. IVien. vol. 

 xxxii. 1872) as occurring on crystals from Svarov and Krusna 

 hora in Bohemia, lout is rejected by Schrauf as insufficiently 

 determined. The distinguishing peculiarities of the Chirbury 

 crystals are (i) the predominance of the plane E which does not 

 truncate an edge as is the case in Carl Urba's crystals ; (2) the 

 frequent occurrence of m and \ ; (3) the tendency of the face o 

 to develop small faces on its edges which are inclined to at 

 angles near 3°. Such faces are Q and Y, and I have since 

 determined a face A on the edge oyn with indices near (25.1.27). 



British Museum, November 26 H. A. Miers 



THE ORIGIN OF CORAL REEFS ' 

 II. 



THE most detailed investigation of coral-reefs which 

 has yet appeared has just been published by 

 Prof. A. Agassiz.'-^ This able naturalist is engaged in 

 prosecuting a series of researches into the biological 

 phenomena of the seas on the eastern side of the 

 United States, under the auspices of the United States 

 Coast Survey, and in the course of these explora- 

 tions he has had occasion to devote himself to the 

 detailed study of the coral-reefs of the Florida seas. 

 For purposes of comparison he has likewise visited the 

 reefs among the West Indian Islands, as well as those on 

 the coast of Central America. His observations are thus 

 the mo^t exhaustive and methodical which have yet been 

 published, and the deliberate conclusions to which he has 

 I ome deserve the most attentive consideration. He 

 traces the history of a coral-reef from its latest stages as 

 dry land to its earliest beginnings, and even beyond these 

 to the gradual evolution of the conditions requisite for 

 the first starting of the reef. His familiarity with the 

 nature of the bottom all over the area in question, and 

 with the life so abundant in the tropical waters, gives him 



C- ntinued from p- ito. 



••On the Torlugas and Florida Reefs." Trn 



.(iSS^). 



a peculiar advantage in this inquiry. The upheaval of 

 recent coral-formations to considerable heights above the 

 sea in various parts of the region enabled him to examine 

 the inner structure and foundations of the reefs, and to 

 obtain therefrom altogether new data for the solution of 

 the problem. Following him in his induction we are led 

 back to a comparatively recent geological period, when 

 the site of the peninsula of Florida was gradually upraised 

 into a long swell or ridge, having its axis in a general 

 north and south direction, sinking gently towards the 

 south, but prolonged under the sea as a submarine ridge. 

 The date of this elevation is approximately fixed by the 

 fact that the V^icksburg limestone was upraised by it, and 

 this limestone is assigned to the Upper Eocene series. 

 As a consequence of the elevation, a portion of the sea- 

 bottom was brought well up into the waters of the Gulf 

 Stream, which were probably shifted a little eastward. 



No marine fauna yet explored equals in variety of forms 

 or number of individuals that which peoples the waters of 

 the Caribbean Sea and the Gulf of Mexico from the depth 

 of 250 to about TOGO fathoms. This prolific life is traced 

 by Prof Agassiz to the copious food-supply carried by 

 the warm tropical currents, combined with the food borne 

 outwards from the sea-board of the continent. The cor- 

 responding abundant fauna found by the Challenger in 

 the Japanese current may be regarded as its counterpart 

 in the Pacific Ocean. Prof. Agassiz points also to the 

 diminished richness of the fauna on the western side of 

 the continents as being probably connected with the 

 absence of those warm equatorial currents which bring 

 such an abundant supply of food to the eastern shores. 

 "No one," he remarks, " who has not dredged near the 

 hundred-fathom line on the west coast of the great 

 Florida Plateau can fonn any idea of the amount of 

 animal life which can be sustained upon a small area, 

 under suitable conditions of existence. It was no un- 

 common thing for us to bring up in the trawl or dredge 

 large fragments of the modern limestone, now in process 

 of formation, consisting of the dead carcasses of the very 

 species now living on the top of this recent limestone." 

 Mollusks, echinoderms, corals, alcyonids, annelids, 

 Crustacea, and the like, flourish in incredible abundance 

 on the great submarine banks and plateaux, and cover 

 them with a growing sheet of limestone, which spreads 

 over many thousands of square miles and may be 

 hundreds of feet in thickness. In these comparatively 

 shallow waters, and with such a prodigiously prolific 

 fauna which supplies constant additions to the calcareous 

 deposit, the solvent action of the carbonic acid upon the 

 dead calcareous organisms is no doubt reduced to a 

 minimum, so that the growth of the limestone is probably 

 more rapid than on almost any other portion of the sea- 

 bottom. 



From the charts we learn how extensively submarine 

 banks are developed in the West Indian region in the 

 track of the warm currents. East of the Mosquito Coast, 

 in Central America, one of these banks may be said to 

 stretch completely across to Jamaica. Similar banks rise 

 off the Yucatan coast ; likewise on the windward side of 

 the islands, where the ocean currents first reach them. 



That these banks lie upon volcanic ridges and peaks 

 can hardly be doubted, though we have no means of tell- 

 ing what depth of recent limestone may have accumulated 

 upon them. Among the islands, recent volcanic masses 

 rise high above sea-level, in Martinique reaching a height 

 of more than 4000 feet. And as usual in volcanic regions 

 there are numerous proofs of recent upheaval, such as 

 the Basse Terre of Guadaloupe, the successive terraces of 

 recent limestone in Barbadoes, and the upraised coral- 

 reefs of Cuba, which lie at a lieight of 1 100 feet above 

 sea-level. 



The West Indian seas have long been famous for their 

 coral-reefs. Prof. Agassiz insists that the distribution of 

 these reefs is determined by the direction of the food- 



