In the article on Terraces in your last number, Mr. G. Poulett Scrope evidently did not intend writing in a style that would bear being minutely criticized, or he was not sufficiently particular in quoting from my work and representing my present views. As it stands, a reader of Mr. Scrope's article would receive impressions very different from those which a perusal of my chapter on Raised Beaches and Inland Terraces would leave on his mind. Such being the case, I am sure Mr. Scrope will pardon me if I make a few remarks in self-vindication.

I have lately been urged to revise the Cretaceous species of Entomostraca, enumerated in my Monograph, published by the Palæontographical Society in 1849. This I ought to have done ten years ago, after the publication of memoirs on the Cretaceous Entomostraca of Germany, the Netherlands, etc., by Reuss, Bosquet, and others, wherein some of my determinations of species are corrected from actual comparison of specimens. An improved classification was attempted in my Monogr. Tert. Entom., 1856; but a total revision is still more necessary now, because the late researches by Sars and G. S. Brady, in the structure and character of the recent Entomostraca, have multiplied and elucidated species and genera of these little bivalved Crustacea to an amazing extent. So clearly has Mr. Brady's “Monograph of the recent British Ostracoda” (Linnean Soc. Trans., 1868), in particular, defined the several groups, that we may in very many cases form a safe opinion of alliances from the shape, hinge, and other characters of the carapace-valve, at least far more satisfactorily than when in 1849 (Monogr. Cret. Entom.), and in 1856 (Monogr. Tert. Entom.), I laboured to institute some definite distinctions for fossil Entomostraca, founded on these characters.

Of the existence of Annelides during the Silurian period we are almost as uncertain as of the existence of plants. Indeed, we might reasonably doubt whether any Silurian fossils can with certainty be referred to this class.

The total thickness of Millstone Grit in North Wales does not quite reach 300ft. This thickness is, I am aware, considerably below that given by several authors, who notice this formation incidentally; but I am prepared to say, from. actual and computed measurement, made on the spot, that the above figures are substantially correct. The Carboniferous system, from the base of the Mountain Limestone to that of the Coal Measures in North Wales, is but an epitome of the same beds in the North of England, the middle member, the grits and sandstones, being thin in proportion.