4o6 



NATURE 



[Sept. 12, 1872 



point, and it is no disadvantage if this zero point be an arbitrary 

 one. When we come to express numerically the amount of 

 p(35iliveness or negativeness of these oxides and hydrites, it will 

 lie necessary to have a zero point, and a very convenient one is 

 that which corresponds pretty nearly to the generally understood 

 limit between bases and acids, and depends upon the direction 

 ill which the action takes place. 



SECTION C— Geology 



()// ///t' Canthrian and Silivinn Hods of Ramsey Island, St. 

 Da-'id's, by Henry Hicks, F.G.S.* 



In a report to the British Association in 1S66, by the late Mr. 

 Salter and the author, Ramsey Island was mentioned as a part of 

 the dis'rict which had been examined and a short description of 

 the ro -ks exposed there was given. At thit time three distinct 

 f.irmxti )ns in succession had been recognised, and also correlated 

 by th-ir fossil contents and lithological characters w.th the Li 1- 

 giila lligs, the Tremadoc group, and the Arcnig group. .S;nce 

 then the author has further eximined these beds, and recently 

 along with Messrs. Homfray, Li^htbody, Kirshaw, and Hopkin- 

 son. 



Daring these researches numerous new forms have been nis- 

 covered in these rocks, and many additional and interesting facts 

 observed. In a section at the north end of the ibland the follow- 

 ing rocks occur in succession : — 



1. [Jtii^iila Flags. — A series of hard siliclms sandstones with 

 grey llaky slate, about 600 feet in thickness, and containing 

 I.ini^uhila Davisiixn gre it abundance but no other fossils save 

 worm tracks and burrows, and --ome plantdike markings. 



2. 7'rt-niaiioi: Group. — Bluish grey flag, and earthy grey rock 

 of a tough texture, from Soo to 1,000 feet in thickness. Fossils 

 are very abundant throughout the whole series, and nearly all the 

 species as well as many of the genera are new. They comprise 

 Jirachiopods of the genera Lingiila, Obo!c!la, and Orthis, and 

 Lamelllbranchs of the genus C/iv;U(/o«/(7. There are also tvo 

 specie; of Orthoceras, a Thcca, a BcUcfophou, an Eiicriniti: and 

 a star fish, and nine species of Trilobites belonging to the 

 genera Dikdoccphalns, Couoiorxp/ie, Ntobc, Asapluis, Chi'iritrus, 

 and Calymcnc, and a supposed land plant named Sofhyton 

 iwplanatmn. Some of these genera are characteristic ot the 

 Cambrian rocks, and others of the .Silurian ; and there are 

 several fo'ms which had not previously been discovered in io;ks 

 of so early an age. Until the discovery of these rocks at St. 

 David's the Tremadoc group was supposed to be a local forma- 

 tion only. 



3. Aronig Group. — A series of ironstained slates and flags, 

 having a thickness of 1,000 feet. The fossils comprise Trilobites 

 belonging to the genera Asaphus, Ogygia, Oegliua, Triinic/eus, 

 A/npv.x, Calyjncnt\ and Agnostus ; also a Conuhiria., T/ura, 

 Orthoccras, Biilcrophoii, Lingula, and Orl/iis, and about 20 

 species of Graptolites. 



In this section the succession from the Cambrian to the Silu- 

 rian rocks i.s probably better shown than at any other place in 

 Britain. 



SECTION D.— Biology 



DSPARTMIiXT OF ZOOLOGY AN'D BOTAVY 



Siroiid Siipplciucnlary Report on the e.xtinet Birds of the Mas- 

 carene Islands, by Alfred Newton, F.R.S. 



The speaker stated that a portion of the grant unexpended at 

 the last meeting of the Association hid been expended by his 

 brother in a renewed examinatioa of the caves in the island of 

 Rodiiguez. This has been conducted by Mr. George Jenner, 

 lately Chief Executive Officer of the idand. No detailed ac- 

 count could at present be given. Several missing parts of the 

 skeleton of Pezophaps, and of additional remains of the large 

 Psittacine bird, described from a single fragmentary maxilla by 

 Milne Edwards as PsittaensC') rodericauus. This mayjenablc its 

 affinities to be more exactly determined, and also allow more 

 light to be thrown on P. niaurilianus of Owen. A bird described by 

 Leguat, and hitherto believed to be extinct, had been found still 

 to exist, and had been described by himself as Paltcornis ex- 

 siil. The remains of a Rallinc bird, considered to be allied to 

 Ocydromus Milne Edwards, was disposed to identify with the 



•The discussion referring to this paper occurs at p. 383 {after Mr. Hopkin- 

 son's p.iper.) 



" Gelinotte " of Leguat, the nature of which had hitherto only 

 been a matter of guess. 



Dr. Sclater said it was well to bear in mind that Rodriguez 

 was one of the stations where it was proposed to place a stalf of 

 astronomers to observe the transit of Venus, and the oppor'unity 

 of carrying on ornithological observational the same time should 

 not be lost sight of. 



On the Perforating Instrument of Pholas Candida, by Mr. 

 John Robertson. 



The author attributed the perforating action of the animal to 

 a rasping effected by the rotatory movements of the shell and 

 also by putting the valves together. 



Prof. AUman saii that the late Mr. Bryson, of Edinburgh, 

 had observed the habits of the Pholas, and had come to the 

 conc'usion that the boring was effected by the foot charged with 

 silicious particles and acting like the leaden wheel of the 

 lapidiry. 



Mr. Gwyn Jeffrc-ys was of opinion that in the whole of the 

 perforating conchifera and some of the univalves the foot was the 

 instrument of perforation. In Cardium, Mactra, and especially 

 Solen, as well as other bivalve mollusca, the posterior extremity 

 of the shell was shaped to receive the foot which worked like a 

 gardener's dibble. In the case of Pholas djctylus, Mr. Caillaud 

 thought thit at Nantes the gneiss was perforated by the rasping 

 action of the shell. Man might do this, but it was doubtful 

 whethc-r it could be accomp^shed in this w,iy by the Pholas. 

 In Teredo navalis he believed that, as Sellius had shovn in 1733 

 in his work " lit Teredine Marina," the foot was the sole in- 

 strument of perloration, and in this case the posterior extremity 

 of the shell had a large excavation to receive the foot. Agiin, 

 Pholadiilea in a young state excavated by means of its foot, bat 

 afterwards the aperture was closed by gelatinous matter, the ani- 

 mal became encysted, and no further excavation took place. The 

 limpet he had seen in Aberdeenshire excavate the rock to the 

 depth of a fuurth of an inch, and this could only hive been 

 accomplished by the foot. In Pholas also no part of the shell 

 can act at the bottom of the excavation. The prickles it was 

 supposed were renewed ; but this could not take pl-ace through- 

 out the shell, and many excavating shells had no prickles at all. 

 Deshayes had advocated the chemical theory ; but this too had 

 been exploded, as Deshayes himself admitted. 



.Summary of Floiueriug Plants of Susse.x, by W. B. Memsley. 



Taking Babington's Manual (5th Edition) as a standard, the 

 Flora of Sussex includes 1,059 species of flower ng plants, 

 reckoning Ferns and Horsetails as well. These last amount to 

 only 'i,'},, or about 3 per cent. Roughly speaking J are Dicotyledons 

 and i Monocotyledons ; 881 per cent of the species are herba- 

 ceous, and III woody; 27 J per cent are annuals, and 72 J 

 perennial; 12 natural orders include rather more than hilf the 

 whole number of species ; 76 of the species are maritime, and 

 56 peculiar to the chalk. Pyrola media, Ilabenaria albida, and 

 Festuca sylvatica are outlieis ot ^Vatson's Scottish type not 

 found in adjacent counties. The three species peculiar to Sus- 

 sex, Phyteuina spieatum, Lonicera Xylostenm, and Trifolium 

 stellatum are probably all introductions, the last being certainly 

 so. In the centre of the county the heath grows as high as 

 three or four feet, and covers considera'^le tracts of land. 



Prof Lawson in answer to a speaker who had inquired the 

 use''ul purpose of these investigations into indigenous plants, and 

 who had lamented the want of adequate knowledge how to keep 

 them in their place, pointed out that the researches of Messrs. 

 Lawes and Gilbert were hkely to lead to practical methods of 

 developing the U'e'ul constituents of pasture an-J of restraining 

 the growth of the undesirable elements. He was especially 

 struck with the presence of Centaurea calcitrapa about Brighton. 

 This he had generally seen as a ballast plant, and thought 

 almost certainly an introduction. 



Diversity of Evolution under Uniform External Conditions, 

 by Rev. John T. Guhck. 



The terms " Natural Selection " and " Survival of the 

 Fittest " present dilTcient phases of a law which cin act only 

 where there is variation. Does this variation ever produce from 

 one stock ditinct varieties and species, while the external con- 

 ditions remain the same? When a species is subjected to a new 

 set of conditions, does the change that is brought about in the 

 organism expend itself in pro.lucing just one new species com- 

 pletely fitted to the conditions, or m.ay it produce many that are 

 equally fitted ? Facts in the geographical distribution and varia- 



