ANNIVERSARY ADDRESS OF THE PRESIDENT. Iv 



but even then the wave-action would modify the outhne of the groove 

 produced ; and, as regards the wearing of the valleys, it scarcely 

 seems possible that any regular and continuous excavation could be 

 produced by a succession of starts, each 1000 feet in extent, with in- 

 tervening intervals of rest *. 



Mr. Sharpe's palseontological papers are of considerable interest 

 and value. For a genus of Gasteropodous shells abundant in Por- 

 tugal he proposed (1849) the name Tylostoma^ considering it distinct 

 from Globiconchay NaticUy and Phasianella. The genus Nerincea he 

 enriched with six new species ; dividing it into four subgenera — Neri- 

 ncea ^b species, Nerinella 10, Trochalia Q,Ptygmatis 12, besides eight 

 species which he thinks ought to be placed in other genera ; so that 

 this genus of fossil Gasteropods is alone supposed to exhibit at least 

 93 species ; — one of the many examples of the extraordinary multi- 

 plication of species in those early ages, — so great indeed as to force 

 upon the mind of every one the necessity of caution and vigilance in 

 attempting to establish new species at periods when it is very pos- 

 sible the range of variation may have been greater than it now is, 

 whilst the characteristic of colour, and often that of either external 

 or internal markings, are lost. Twelve species were found in Portugal, 

 six of which had been previously described as cretaceous species ; so 

 that Mr. Sharpe concluded that the Nerincece in Portugal or the 

 South of Europe are cretaceous fossils, whilst in the North they are 

 oolitic. 



Sir Charles Lyell having submitted to Mr. Sharpe for examina- 

 tion the fossils he had collected in North America, the result was a 

 very able analytical paper (1848) on the Mollusca of the collection, 

 being so far an estimate of the labours of the United States Geologists. 

 Referring to Mr. Hall's table, in which five subdivisions are enume- 

 rated below the equivalent of the Llandeilo flags, Mr. Sharpe disputes 

 this last position, and asserts that there are no grounds for believing 

 that any of the beds are of an earlier age than the Lingula beds of 

 North Wales. At the same time Mr. Sharpe admits that no species 

 found in any bed below the Trenton limestone, the upper of the five 

 beds in question, are identical with those of England, though in the 

 Trenton rock many such Lower Silurian fossils have been found; but 

 he considers that the presence of Lingulae, though not of the same 

 species, in the Potsdam sandstone, the lowest American fossiliferous 

 deposit, may well justify the assumption of its being equivalent to 

 the Lingula-flags of North Wales. The great subdivision of the 

 strata in Hall's table is considered a source of difficulty, and doubt- 

 less the separation of several limestones from each other, when so 

 nearly parallel, must lead to great misconception, the supposed equi- 



* Our lamented friend often observed, in respect to this paper, " What will the 

 Swiss geologists say ? " One Swiss geologist, M. De la Harpe, has answered 

 this appeal by an able criticism of the paper, in which he not only endeavonrs to 

 show that the evidence is insufficient to determine the permanency of level of the 

 lines of erosion, or the synchronism of those lines with the terraces of Alpine 

 valleys, but also adduces much of the argument I have myself advanced in 

 the above remarks. 



