upon crystalline schists. The Primal division was regarded by the Messrs. Rogers as the equivalent both of the Potsdam and the still lower members of the Cambrian.

Auroral, (II.) This division, which, with the last, includes the first fauna, consists in great part of magnesian limestones, and corresponds to the Calciferous and Chazy formations. Its thickness in Pennsylvania varies from 2500 to 5000 feet, and with the preceeding division, it includes the first fauna. The representatives of the Primal and Auroral divisions attain a great development in eastern Tennessee, where they have been studied by Safford.

Matinal, (III.) In this, which represents the second fauna, were comprised the limestones of the Trenton group, together with the Utica and Hudson-River shales.

Levant, (IV.) This division corresponds to the Oneida and Medina conglomerates and sandstones.

Surgent, Scalent and Pre-Meridional (V. VI.) In these divisions were included the representatives of the Clinton, Niagara and Lower Helderberg groups of New York, making, with division IV., the third fauna.

The parallelism of these divisions with the British rocks was most clearly and correctly pointed out by H. D. Rogers himself, in an explanation prepared, as I am informed, with the collaboration of Prof. William B. Rogers, and published in 1856, with a geological map of North America by the former, in the second edition of Keith Johnson's Physical Atlas. The paleozoic rocks of North America are there divided into several groups, of which the first, including the Primal, Auroral and Matinal, is declared to be the near representative of "the European paleozoic deposits from the first-formed fossiliferous beds to the close of the Bala group; that is to say the proximate representatives of the Cambrian of Sedgwick." A second group embraces the Levant, Surgent, Scalent and Pre-Meridional. These are said to be "the very near representatives of the true European Silurian, regarding this series as commencing with the May-Hill sandstone." The Levant division is farther declared to be the equivalent of the sandstone just named; while the Matinal is made to correspond to the Llandeilo, Bala or Upper Cambrian; the Auroral with the Festiniog or Middle Cambrian; and the Primal with the Lingula flags, the Obolus sandstone of Russia and the Primordial of Bohemia.

The reader of the last few pages of this history will have seen how the Silurian nomenclature of Murchison and the British Geological Survey has been, through Lyell, de Verneuil and the Canadian Survey, introduced into American geology in opposition to the judgment, and against the protests of James Hall and the Messrs. Rogers, the founders of American paleozoic geology.

Three points have I think, been made clear in the first and second parts of this sketch: First, that the series to which the name of Cambrian was applied by Sedgwick in 1835, (limited by him as to its downward extension, in 1838) was co-extensive with the rocks characterized by the first and second faunas. Second, that the series to which the name of Silurian was given by Murchison in 1835, included the second and third faunas; but that the rocks of the second fauna, the Upper Cambrian of Sedgwick, were only included in the Silurian system of Murchison by a series of errors and misconceptions in stratigraphy, on the part of the latter, which gave him no right to claim the rocks of the second fauna as a lower member of his Silurian. Third, that there was no ground whatever for subsequently annexing to the Silurian of Murchison, the Lower and Middle Cambrian divisions of Sedgwick, which the latter had separated from the Upper Cambrian on stratigraphical grounds, and which were subsequently found to contain a distinct and more ancient fauna.

The name of Silurian should therefore be restricted, as maintained by Sedgwick and by the Messrs. Rogers, to the rocks of the third fauna, the so-called Upper Silurian of Murchison; and the names of Middle Silurian, Lower Silurian, and Primordial Silurian banished from our nomenclature. The Cambrian of Sedgwick however includes the rocks both of the first and second faunas. To the former of these, the lower and middle divisions of the Cambrian, (the Bangor and Festiniog groups of Sedgwięk,) Phillips, Lyell, Davidson, Harkness, Hicks and other British geologists, agree in applying the name of Cambrian. The great Bala group of Sedgwick, which constitutes his Upper Cambrian, is however as distinct from the last as it is from the overlying Silurian, and deserves a not less distinctive name than these two. Its original designation of Upper Cambrian, given when the zoological importance of Lower and Middle Cambrian was as yet unknown, is not sufficiently characteristic, and the same is to be said of the name of Lower Silurian, wrongly imposed

447 upon it. The importance of this great Bala group in Britain, and of its North American equivalent, the Matinal of Rogers,including the whole of the limestones of the Trenton group, with the succeeding Utica and Hudson-River shales,-might justify the invention of a new and special name. That of CambroSilurian, at one time proposed by Sedgwick himself, and adopted by Phillips and by Jukes, was subsequently withdrawn by him, when investigations made it clear that this group had been wrongly united with the Silurian by Murchison. Deference to Sedgwick should therefore prevent us from restoring this name, which moreover, from its composition, connects the group rather with the Silurian than the Cambrian. Neither of these objections can be urged against the similarly constructed term of Siluro-Cambrian, which moreover has the advantage that no other new name could possess, of connecting the group both with the true Silurian, to which it has very generally been united, and with the Cambrian, of which, from the first, it has formed a part. I therefore venture to suggest the name of Siluro-Cambrian, as a convenient synonym for the Upper Cambrian of Sedgwick, (the Lower Silurian of Murchison,) corresponding to the second fauna; reserving at the same time the name of Cambrian for the rocks of the first fauna,—the Lower and Middle Cambrian of Sedgwick, and restricting with him the name of Silurian to the rocks of the third fauna, the Upper Silurian of Murchison.*

The late Prof. Jukes, it may here be mentioned, in his Manual of Geology, published in 1857, still retained for the Bala group the name of Cambro-Silurian (which had been withdrawn by Sedgwick in 1854) and reserved the name of the "true Silurian period" for the Upper Silurian of Murchison. In his recent

* Dr. Dawson, in his address as president of the Natural History Society of Montreal, in May 1872, has taken the occasion of the publication in the Canadian Naturalist, of the first and second parts of this sketch, to review the subject here discussed. Recognizing the necessity of a reform in the nomenclature of the paleozoic rocks, in conformity with the views of Sedgwick, he would restrict to the rocks of the third fauna the name of Silurian, making it a division equivalent to Devonian; and while reserving with Lyell, Phillips and others, the name of Cambrian for the first fauna only, agrees with me in the propriety of adopting the name of Siluro-Cambrian for the second fauna.

and much improved edition of this excellent Manual (1872), Prof. Giekie, the director of the Geological Survey of Scotland, has substituted the nomenclature of Murchison; with the important exception, however, that he follows Hicks and Salter in separating the Menevian from the Lingula-flags, and uniting it with the underlying Harlech rocks (as has been done in the table on page 312), giving to the two the name of Cambrian [loc. cit., pages 526-529], and thus, on good paleontological grounds, extending this name above the horizon admitted by Murchison. Barrande, on the contrary, in his recent essay on trilobites (1871, page 250), makes the Silurian to include not only the Lingulaflags proper (Maentwrog and Dolgelly), but the Menevian, and even a great part of the Harlech rocks themselves (the Cambrian of Murchison and the Geological Survey), for the reason that the primordial fauna has now been shown by Hicks to extend towards their base. This, although consistent with Barrande's previous views as to the extension of the name Silurian, is a still greater violation of historic truth. By thus making the Silurian system of Murchison to include successively the Upper Cambrian and the Middle Cambrian of Sedgwick, and finally his Lower Cambrian, (the Cambrian system of Murchison himself,) we seem to have arrived at a reductio ad absurdum of the Silurian nomenclature; and we may apply to Siluria, as Sedgwick has already done, the apt quotation once used by Conybeare, with reference to the Graywacke of the older geologists, which it replaces; "est Jupiter quodcunque vides."

It would be unjust to conclude this historical sketch of the names Cambrian and Silurian in Geology, without a passing tribute to the venerable Sedgwick, who to-day, at the age of eighty-seven years, still retains unimpaired his great powers of mind, and his interest in the progress of geological science. The labors of his successors in the study of British geology, up to the present time, have only served to confirm the exactitude of his early stratigraphical determinations; and the last results of investigations on both continents unite in showing that in the Cambrian series, as defined by him more than a generation since, he laid, on a sure foundation, the bases of paleozoic geology.

SEXUAL SELECTION IN MAN.

BY H. ALLEYNE NICHOLSON, M.D., D.Sc., F.R.S.E., Professor of Natural History and Botany in University College, Toronto. "Sexual selection" is the term employed by Darwin to denote a twofold winnowing, to which he believes that the individuals of many species of animals are subjected. On the one hand, certain males being stronger and more powerful than the others, succeed in leaving descendants behind them, whilst other weaker males do not get the opportunity of perpetuating their peculiarities, the female in this case remaining passive. On the other hand, it is believed that in some cases the females have the power of choosing their mates, and that they select such males as please them best, whether this be in consequence of some peculiarity of form, colour, or voice, or as a result of some undefinable attraction. In this process the selection lies with the female, and the male re mains passive, in any other sense than that he does what he can to secure that the choice of the female shall fall upon him instead of upon any other of his rivals. In either case Mr. Darwin believes that great modifications have been produced in this way, and that many animals owe to this cause some of their most striking peculiarities. Mr. Darwin, in fact, has so far abandoned his former belief in the efficacy of "natural selection" as an agent in producing the differences which separate different species of animals, as to admit that some supplementary cause must, in some cases at any rate, be looked for; and this he thinks is to be found in the action, through long periods, of "sexual selection."

Without entering into the question of the extent to which Mr. Darwin's views may be depended on as regards animals, we purpose here very briefly to survey his application of the theory of sexual selection to the case of man. In so doing we shall glance at the leading propositions laid down in Chapters XIX and XX of the "Descent of Man," examining in greater detail those which appear to be of the highest importance. It may as well be premised, however, that there are two distinct aspects to the question of sexual selection, in the case of all animals alike, but especially in the case of man. It is one thing to admit the existence of

VOL. VI.

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