Feb. 23, 1888] 



NATURE 



393 



Microsauria and Dendrerpeton. 



In the notice in Nature of January 12 (p. 244) of Fritsch's 

 new number of his excellent work on the Permian fauna of 

 Bohemia, which has not yet reached me, I observe a 

 reference to Microsauria, which would seem to imply that I 

 had included Dendrerpeton in that group. Possibly this was not 

 intended by the reviewer, as it certainly could not have been 

 intended by Fritsch, who knows my views quite well ; but in 

 case it should be misunderstood I beg to say that I have not held 

 this view, but on the contrary have confined the name Micro- 

 sauria to species with simple teeth, and have placed Dendrerpeton 

 with Labyrinthodonts, though by no means as a typical genus of 

 that group. In my last paper on this subject (Trans. Royal 

 Society, 1882), I expressly exclude the two species o{ Dendrerpe- 

 ton referred to from Microsauria, and define the latter as having 

 non-plicated teeth (pp. 634-35). ^ ™^y ^^^^ however, that I 

 have always held and now hold that the Microsauria, though in 

 some respects inferior to Labyrinthodonts, embrace in their 

 structures premonitions of the true reptiles not found in the 

 latter. 



The study of these creatures was one of those bye-efforts 

 thrust on me by circumstances, and which I have closed up so 

 far as I am concerned in the paper referred to ; but I have 

 learned to love the little Microsaurs and to regard them as a 

 hopeful and prophetic group. J. Wm, Dawson. 



McGill College, January 26. 



A New Historic Comet .' 



Permit me to inform Mr. Knott that the "new historic 

 comet " is not a new comet at all. He will find it as No. 154 in 

 Mr. Chambers's Catalogue No. II. in his well known " Hand- 

 book of Descriptive Astronomy." It is there described, 302 A. D. 

 "in May-June a comet was visible in the morning — (Ma-tuoan- 

 lin: Williams 26)." W. H. S. MoNCK. 



Dublin, February 10. 



The Proposed Teaching University for London. 



No one, I am sure, who has carefully real my letters in the 

 Times on this subject could agree with the writer of your article 

 that I appear "to consider the dispute as one between the 

 efficiency of ' lectures ' on the one hand, and of ' reading ' on the 

 other. " 



The writer of the article has certainly misunderstood my views 

 "upon the matters in dispute," as well as my object in quoting 

 Darwin's dictum on the advantages of "reading" as compared 

 with "lectures." Philip Magnus. 



Exhibition Road, London, S.W., February 10. 



Institute of Chemistry. 



With reference to a circular letter dated the 12th inst., and 

 bearing the signature of Mr. W. Thomson, which has been sent 

 to the Fellows of the Institute of Chemistry, we beg that you 

 will be so good as to allow us to infor.n the Fellows, through 

 your columns, that we have not been consulted in regard to the 

 action taken by Mr. Thomson, and that we decline to offer our- 

 selves as candidates for election in opposition to the nominations 

 of the Council. Boverton Redwood. 



London, February 20. Alfred Gordon Salamon. 



CORAL FORMATIONS. 



T DESIRE to call attention to a condition of reef that 

 -^ I think has been very little studied, but that may 

 contain a clue to a solution of some of the difficulties 

 that still surround the subject of coral formations 

 generally. 



I may as well at once avow myself to be one of those 

 who, on reviewing the later evidence on coral growth, 

 have come to the conclusion that it is sufficient to justify 

 an abandonment of the supposition that subsidence plays 

 a principal part in the production of barrier reefs and 

 atolls, but are at the same time not satisfied with one 

 part of the explanation offered by Mr. J. Murray. 



I refer to the great effects attributed by him to the 

 disintegration and solution of dead coral by the chemical 



action of sea-water, in hollowing out and deepening the 

 large and deep lagoons inside both these classes of reefs. 



Mr. Murray's theory on this point, as summarized by 

 himself, is that — 



"(i) When coral plantations build up on submarine 

 banks, they assume an atoll form, owing to the more 

 abundant supply of food to the outer margins, and the 

 removal of dead coral rock frojn the interior portions by 

 currents and by the action of the carbonic acid dissolved 

 in sea-water. (2) That barrier reefs have built out from 

 the shore on a foundation of volcanic debris, or a talus 

 of coral blocks, coral sediment, or pelagic shells, and the 

 lagoon channel is formed in the saine way as a lagoon." 



The italics are mine, and indicate the part of his theory 

 to which from my view, and, I believe, that of others, 

 there are objections, but to which Mr. Murray attaches 

 considerable weight. 



Is it necessary thus to invoke the aid of dissolution of 

 the dead coral by chemical action as an important agent 

 in the formation of these deep lagoons and channels ? I 

 think not. 



An examination of the forms of, and depths on, well- 

 surveyed submerged banks in different regions reveals a 

 considerable number of reefs, which, if their development 

 continues on the same lines as apparently heretofore, 

 must, in the course of time necessary to bring them to 

 the surface, form perfect atolls of large size, inclosing 

 deep lagoons, without any further scooping out by 

 solution. 



Many instances occur in the China Sea. The Tizard 

 Bank, in lat. 10' 20' N., and long. 1 14° 25' E., is 32 nautical 

 miles in length, with an extreme breadth of 10 miles, and 

 was well surveyed in 1867. The central portion is very 

 flat and almost void of patches. Its depth is from 30 

 to 47 fathom?. Its edge is crowned with a coral rim 

 varying from 4 to 10 fathoms in depth, broken here and 

 there by openings, in some cases over 30 fathoms deep. 

 The bank rises steeply from deep water, but, as no sec- 

 tional soundings were taken, the precise angle of slope 

 is unknown. The rim is composed of coral in luxuriant 

 growth, and it can scarcely be doubted that in time it 

 will reach the surface. In fact, on its periphery of 100 

 miles, in eight places small patches of reef, three of 

 which bear islets, have already done so. 



When the remaining portions of the rim are also 

 awash, the reef will be in all respects an atoll similar 

 to the great Maldive atolls, without any necessity for 

 solvent action enlarging or deepening it. 



Eight other banks of similar character, and in various 

 stages, occur not far from this reef. 



The great Macclesfield Bank, farther north, over 70 

 miles in length, and 40 miles in width, is of precisely the 

 same nature, but its development is not so far advanced ; 

 the rim being in no spot nearer the surface than 10 

 fathoms, the water on it varying from that amount to 19 

 fathoms, while the depth of the inclosed area is from »^ 

 to 60 fathoms. The survey of this bank is -^^ />^ u^^^^" 

 plete as in the case of some others. b"<^ enough has been 

 done to show its character very plainly. ^ , „. 



The Prince Conaurt Shoal (300 miles S.W. of the Tizard 

 Bank) is apparently at a still earlier stage, a few patches 

 of 17 fathoms and a considerable area of 30 fathoms 

 partly inclosing a central area of 40 fathoms depth. The 

 great Seychelles Bank in the Indian Ocean, 200 miles by 

 TOO, is very imperfectly known, but in most places the 

 lines of soundings over its edge exhibit this tendency to 

 form a rim. Here, however, the general depth on the 

 bank is not over 30 fathoms. The Amirante Bank is a 

 similar example. 



Theevidence afforded by these reefs has probably escaped 

 notice from the fact that as published in charts for the pur- 

 pose of navigation they are mostly shown on a very small 

 scale, in which their character is scarcely apparent. The 

 original manuscript surveys in the records of the Hydro- 



