NA TUBE 



148 



disease " which attacks in so painful a manner the manu- 

 facturers of lucifer matches, and which can be so com- 

 pletely obviated by the employment in their construction 

 of red instead of ordinary phosphorus, because the fornier 

 does not give rise to the formation of acid fumes when 

 exposed to the air, and therefore does not attack the 

 mouth and teeth. There is one subject on which we 

 have looked, but in vain, through this volume for informa- 

 tion • it is for the explanation of how it is that tootli- 

 disease and civilisation so unfortunately go hand m 

 hand. The work will be found of special interest to all 

 students of surgery. 



LETTERS TO THE EDITOR 



r The Editor does not hold himself responsible for opinions expressed 

 bv his correspondents. A either can he undertake to return, 

 or to correspond with the writos of, rejected manuscripts. 

 No notice is taken of anonymous communications.^ 

 Deep-sea Researches 

 When Prof. WyviUe Thomson published his recent volume 

 fiiving the results of the deep-sea researches conducted by him- 

 felf and his colleagues, Dr. Carpenter, Mr. Jeffleys and o hers 

 he also cave a sketch of the history of the subject ; but he iiiade 

 no mention of my memoir on the Microscopic Organisms of the 

 Levant Mud, pubUshed in 1847 m the Transactions of the 

 Literary and Philosophical Society of Manchester, though this 

 memoir had been referred to from time to time by Dr. Carpenter, 

 Messrs. Parker and Rupert Jones, and others, and was next to 

 Ehrenberg's discovery of the microscopic structure of chalk, the 

 startinp-point of all these deep-sea investigations. It was the 

 first to call attention to the existence of ioraminilerous deposits 

 in the sea and to insist upon the organic origin of all hmestones 

 except a few freshwater Travertins, in opposition to the theory 

 of chemical deposits that had previously been advocated in tlie 

 works of Phillips and other geologists. I do not care very nuch 

 about these questions of priority of oUervation, but since IJr. 

 Wvville Thomson's article in Naturf, vol. xi. p. 1 16, dwells 

 larcely upon another point, which was also brought prominently 

 forward in my memoir, 1 think it worth while preventing a repe- 

 tition of the oversight, because the two subjects referred to, viz. 

 the foraminiferous origin of calcareous deposits, and the subse- 

 quent modification of such deposits by the agency of carbonic 

 acid cas, now prove, as I long ago insisted that they would do, two 

 of the most important factors in the solution of the problem of 

 the nature and origin of deep-sea deposits. Dr. AVyville 

 Thomson, in the article in question, points out that extensive 

 areas of the deep-sea bottom are now occupied by a reddish earth, 

 and he has arrived at the conclusion that this earth is a residue left 

 after all the calcareous Globigerira; and other such elements 

 have been removed by the solvent action of carbonic acid accu- 

 mulated in these deep waters. In my memoir I arrived at the 

 same conclusion from the study of the marine Tertiary deposits, 

 containing Diatomacea-, of Bermuda, Virginia, and elsewhere. I 

 may perhaps be peimitted to republish the following extr.icts 

 from that memoir, since it is not now readUy accessible to all the 

 numerous naturalists who are interested in this question :— 



" In the recent deposit of the Levant we have generally an 

 admixture of calcareous and siliceous organisms. In seme locali- 

 ties the latter are more sparingly distributed than in others ; in 

 a few instances they are almost entirely absent. The same 

 admixture occurs in the recent sands from the West Indies. The 

 soft calcareous mud from the bottom of the lagoons of the Coral 

 Islands contains a considerable number of similar siliceous 

 forms and corresponding results have been obtained in most of 

 the marine sediments from various parts of the globe, examined 

 by M. Ehrenberg. , . , . , , ■, c t, j j 



"On the other hand, the infusorial deposits of Bermuda and 

 Virginia are altogether siliceous. Not one calcareous organism 

 exists The siliceous forms comprehend the majority of those 

 whicli I have described from the Levant, many of them being 

 not only similar but specifically identical, and the manner in 

 which they are grouped together in these distant localities indi- 

 cates someihing more th.-m mere accident. Indeed, we want 

 nothing but the calcareous structures to render these Myocene 

 strata perfectly analogous to those now in process of formation 

 both in the Mediterranean and in ^the West Indian seas. Are 



\Dec. 24, 1874 



these siliceous deposits, so void of any calcareous organisms, still 

 in the condition in which they were originally accumulated ? or 

 were they once of a mixed character, like those of the Levant, 

 having been subsequently submitted to some chemical action 

 which has removed all the calcareous forms, leaving only the 

 siliceous structures to constitute the permanent stratum ? I am 

 disposed to adopt the latter opinion, for several reasons." 



After showing the resemblance between the residue left after 

 treating certain substances with nitric acid, and the diatomaceous 

 deposits, I proceed to say : — 



" Such deposits, in these present conditions, stand out as 

 anomalies in the existing order of oceanic phenomena, and have 

 nothing resembling them except the local freshwater accumula- 

 tions which occur in various places. Between these, however, 

 no real analogy exists. It must not be forgotten that the Vir- 

 ginian deposit can be traced for above two hundred miles ; and, 

 being marine, would doubtless be mixed up with such marine 

 products as were likely to occur along so extended a line. The 

 only recorded instance with which I am acquainted, that exhibits 

 the slightest resemblance, is furnished by M. Ehrenherg, m his 

 examination of materials brought home from the south pole by 

 Dr. Hooker. Some pancake ice, obtained in lat. 78 10', long. 

 162° W., when melted, furnished seventy-nine species of organ- 

 isms of which only four were calcareous Polythalamia, the 

 remainder being all siliceous. But even this example, remark- 

 able as it is, does not supply us with any real parallelism. The 

 deposits in question have never yet exhibited a single example 

 of a calcareous organism." 



After referring to the European greensands, I continue : — 

 " Nature furnishes us with an agent quite equal to the produc- 

 tion of such effects as we are at present acquainted with. This is 

 carbonic acid gas in solution in water. Mr. Lyell has already 

 availed himself of ihe instrument to account for the subtraction 

 of calcareous matter from imbedded shells, as well as for some 

 of the changes that have taken place in the structure and compo- 

 sition of stratified rocks ... It is easy to conceive that 

 whilst tliese strata were in a less consolidated state than at 

 present, they might be charged with water containing carbonic 

 acid L'as. '1 his would act as a solvent of the organic atom of 

 lime "unlil the acid was neutrahsed." . . . 



After venturing upon these conclusions in 1847, not as 

 mere speculative guesses, but as the deliberate result of a 

 Icng series of investigations carefully worked out, I need 

 scarcely say how intense was the interest with which I 

 read Dr. Wyville Thomson's observ.itions, which so tho- 

 roughly sustain and confirm the accuracy of mine. My con- 

 clusions were wholly derived from the microscopic observa- 

 tions of earths and rock specimens which I compared with the 

 few examples of foraminiferous ooze with which I was then 

 familiar. The Challenger researches now show us how exten- 

 sively the conditions described in my memoir have prevailed ; a 

 fact which coiUd not have been ascertained before the machinery 

 for deep-sea explor.ition attained to its present perfection. But 

 having arrived at them in a decided or definite manner when the 

 materials for doing so were much more scanty than they now 

 are, and when no one except myself and the late Prof. Badey of 

 West Point were giving much attention to the subject, 1 think 

 I am justified in wishing the fact to be placed on record. 

 Owens College, Dec. 12 W. C. Williamson 



Origin of Bright Colouring in Animals 

 The origin of the'.bright colouring of flowers, through natural 

 selection effected by insects, appears to me one of the strongest 

 points of the Danvinian theory. But I think the origin 

 of the bright colouring of many animals, especially birds and 

 insects, is on the contrary one of the greatest of its difficulties. 

 Darwin accounts for it in most cases by sexual selection— the 

 most beautiful males being the best able to obtain mates and to 

 leave offspring. 



In the way of this theory tliere are three very serious difficul- 

 ties, which I think have not been dwelt on as they deserve. 



I. Before special coloration could arise as a specific character, 

 the colours must have been variable ; for selection can work 

 only when it has variation to work with, and it appears incredible 

 that such a cause as sexual selection could ever give them any 

 great degree of fixity. But the bars and spots on the wings of 

 birds .ind butterflies are, as a rule, perfectly definite, and not 

 more variable within the hmits of the same species than any 

 other part of the organism. This difficulty does not apply in 

 the same degree to the origin of the coloration of flowers through 



