70 DE. WALLICH ON THE PHYSICAL 



Here, then, we have placed before us the various opinions enter- 

 tained by geologists down to a very recent date, so far as pub- 

 lished researches are concerned. Before proceeding with my task, 

 however, I must, with a view to prevent my argument from becoming 

 in some measure unintelligible, correct a serious, though obviously 

 an unintentional, misconception on Sir Charles Lyell's part as 

 regards the opinions always entertained and repeatedly expressed by 

 me in print on the subject of the Diatomacece. I allude to the 

 statement, attributed to me, that certain areas of the North Atlantic 

 are " monopolized " by these organisms. So far from this being my 

 opinion, in a correspondence with Sir Charles which took place in 

 January 1870 I stated, in reply to a series of questions he put to 

 me, that I have never swerved from the view that the Diatoms are 

 plants — that my belief is that the whole of the Diatoms met with in 

 the deep-sea deposits have not lived there, but have sunk to the 

 bottom from the surface only after death — and that there is only 

 one group, namely the discoidal, which occurs in such profusion 

 at the surface, not of the North Atlantic, but of the tropical Atlantic 

 and other tropical seas, as to furnish any material contribution of 

 siliceous matter to the deep-sea deposits*. 



It will, no doubt, be remembered that in 1869 the opinion was 

 promulgated by two very distinguished biologists that the "calcareous 

 mud of the Atlantic is not merely a Chalk formation, but a conti- 

 nuation of the Chalk formation ; so that we may he said to he still 

 living in the Cretaceous epoch." On the merits of this question I 

 think it right to say I have no intention of expressing an opinion, 

 my aim in pursuing the present inquiry being limited to an endea- 

 vour to explain, with a fair show of probability, the singularly unique 

 characters and mode of stratification of the Chalk flints. For aught 

 I have now to adduce on the subject, the battle of the epochs will 

 therefore have to be fought out on stratigraphical and palseontological 

 grounds. Nevertheless I feel bound to say that if the evidence fur- 

 nished by the lithological composition of the ancient chalk and recent 

 calcareous mud be correctly interpreted, we shall, at all events, detect 

 in it nothing to warrant the conclusion that in no part of the oceanic 

 areas yet explored is there any thing to be identiJ&ed lithologicaUy 

 with the true Chalk. On the contrary, so far as the prevailing 

 conditions of the existing sea-bed can be compared with those pre- 

 vailing during the Cretaceous period, we shall not even detect valid 



* I would take the opportunity of here stating that a great deal of the mis- 

 conception prevailing as regards the rate and extent to which the purer siliceous 

 deposits are produced by the DiatomacecB and Polycystina is ascribable to the 

 too prevalent practice of making arithmetical computations take the place of 

 observed facts in matters connected with biology. When Ehrenberg remarked 

 that "a single animalcule (meaning a Diatom), perfectly invisible to the naked 

 eye, could, under favourable circumstances, possibly be increased in four days to 

 140 billions of independent animalciiles, that two cubic feet of a stone similar 

 to the polishing-slate or tripoli of Bilin might be formed in four daj-s, and that 

 these, multiplying again during only eight days of undisturbed organic activity, 

 might in the same time afford a mass of silica which would equal the size of the 

 earth," he simply played with figures. (See Scient. Mem. vol. iii. part x,, April 

 1842.) . . 



