TRANSACTIONS OF THE SECTIONS. 83 



As far as I have had an opportunity of judging from the Molluscaof the North and 

 South Atlantic, I am inclined to think that the Arctic and Antarctic currents do 

 not extend heyond tho Equator. The South-Atlantic species procured by the 

 ' Challenger ' party in deep water appear to he different from those of the North 

 Atlantic in similar depths, according to our present notion of species. It is unne- 

 cessary for me to renew my objection to the phrase " representative species," as 

 Sir Wyville Thomson has satisfactorily disposed of the matter in page 14 of his 

 ' Depths of the Sea.' 



It will be seen, on referring to the list of deep-water Mollusca procured in the 

 f Valorous ' cruise, that several of the species are also Sicilian fossils. They occur 

 in the Pliocene formation of the south of Italy. Professor Seguenza has just pub- 

 lished a very complete and valuable catalogue entitled ' Elenco dei Cirripedi e dei 

 Molluschi della zona superiore dell' antico plioceno,' which are arranged in two 

 divisions, " Depositi littorali " and " Depositi suhmarini." But some further dis- 

 tinction would seem to be necessary in order to separate the strata, inasmuch as 

 certain species which are assuredly littoral are included in the submarine division. 

 For instance, Adeem piisillus, Forb. (which lives at depths varying from 40 to 1450 

 fathoms), and Cylichna ovata, J. (G6-8G2 fathoms), are entered in both divisions ; 

 while peculiarly shallow-water species, such as Patella vulgata, Tectum virginea, 

 and six now also living species of Cluton, appear only in the submarine or deep- 

 water division. Many of the species in Segnenza's Catalogue (besides those noticed 

 in the ' Valorous ' list of deep-water Mollusca), which had been previously con- 

 sidered extinct, were discovered hy me in the ' Porcupine ' expeditions to be still 

 living ; and I have no doubt that the rest of the so-called extinct species, from the 

 upper zone of the older Pliocene in Sicily, will sooner or later be detected in future 

 deep-sea explorations. In fact our examination of the ahyssal fauna has been 

 hitherto extremely slight and cursory, taking into account the enormous extent of 

 area, the difficulties caused by unfavourable weather, and the inadequacy of the 

 instruments used in the investigation. Our good neighbours, the Norwegians, 

 have not relaxed in their work ; and while this Address is being delivered their 

 second year's expedition to the Arctic seas will almost have been completed. May 

 every success attend them ! 



There has heen lately a good deal of controversy as to the supposed " continuity 

 of the Chalk ;" and the affirmative of the proposition has been most ably argued by 

 my colleague and friend, Sir Wyville Thomson, in his ' Depths of the Sea.' 



Prof. E. Forbes, in his Report on ^Egean Invertebrata (1844), was, I helieve, the 

 first to state the proposition. He says, at p. 178, that the strata in his lowest 

 region, or 230 fathoms, would, if filled up, " present throughout an uniform mineral 

 character closely resembling that of chalk, and will be found charged with charac- 

 teristic organic remains and ahounding in Foraminifera. "We shall, in fact, have 

 an antitype of the chalk." 



Sir Wyville Thomson supports his view by the weighty authority of Dr. Car- 

 penter, Prof. Huxley, and Prof. Prestwich ; and although the late Sir Charles Eyell 

 entered a vigorous protest against the hypothesis, and went so far as to designate it 

 a " popular error," I will refrain from expressing any opinion of my own, but will 

 content myself with stating a few facts in elucidation of the question. 



The comparison of the deep-sea ooze with the geological formation known as 

 chalk depends on two points, viz. the mineral composition and the organisms 

 belonging to each. 



1. Mineral composition. — The late Prof. David Forbes, whose knowledge as a 

 mineralogist and chemist was universally recognized, furnished me, on my return 

 from the ' Porcupine ' expedition of 1809, with a complete analysis of a sample of 

 Atlantic mud procured at a depth of 1443 fathoms. He proved that it differed 

 from ordinary chalk in containing scarcely more than 50 per cent, of carbonate of 

 lime, whereas chalk consisted all but entirely of carbonate of lime. Indeed Sir 

 Wyville Thomson admits that " a more careful investigation shows that there are 

 very important differences between them." 



2. Organisms. — I must here confine myself chiefly to the Mollusca, which Sir C. 

 Lyell regarded as " the highest or most specialized organization " on which geolo- 

 gical reasoning and classification are founded. 



7* 



