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 similar set of conditions~prevailed at the Jurassic epoch, marked, by the deposition of strata of an estuarine character throughout the whole period. I need here only point out how remarkably this fact confirms the conclusion drawn from other premises by Mr. Godwin- Austen *, of the existence of an extended land-area during the Jurassic period, in the north-European area — reserving the discussion of the other interesting questions suggested by it for the third part of this memoir.

II. The Cretaceous Strata of Scotland.

There are not wanting grounds for inferring, a priori, that rocks of the Cretaceous system once extended over large portions of Scotland ; and this inference has received the strongest support from the discovery, by numerous observers, of chalk-flints in great abundance, with transported masses of Greensand, in the drifts of the north-east of the country, as well as from the fact, recorded by the Duke of Argyll† and Professor Geikie‡, of the existence of beds of chalk- flints, sometimes of great thickness, under the basalts of the Western Isles. But hitherto no rocks of Cretaceous age have been detected in situ in the British Islands to the north of Yorkshire and Antrim. During my study of the Jurassic rocks of Scotland, however, I have had the good fortune to discover very interesting Cretaceous deposits of considerable extent, though often much obscured by overlying volcanic rocks. These occur in the west of Scotland, on the mainland, and also in several of the islands, and, as might be anticipated, present characters similar to those of the equivalent strata of the north of Ireland, of which they are evidently the northern prolongation; at some points, however, they exhibit other features of much novelty and interest, for which we must seek a parallel in the Tourtia and other continental deposits. These Cretaceous strata are also of the greatest interest and importance as affording the most complete confirmation of the conclusions of the Duke of Argyll and Professor Geikie as to the Tertiary age of the Hebridean volcanic rocks.

III. The Triassic Strata of Scotland.

Another formation, the existence of which in Scotland has been considered by some geologists almost as problematical as that of the Cretaceous, is the Trias. The keen discussions, however, concerning the age of the now celebrated reptiliferous sandstone of Elgin appeared to many geologists to be terminated by the palaeontological researches of Professor Huxley, referring to which Sir Roderick Murchison, in the last edition of ' Siluria,' wrote as follows: — " To such fossil evidence as this the field-geologist must bow ; and instead, therefore, of any longer connecting these reptiliferous sandstones of Elgin and Ross with the Old Red Sandstone beneath them, I willingly adopt the view established by such fossil evidence, and consider that these overlying Sandstones and limestones are of Upper


 * Quart. Journ. Geol. Soc. vol. xii. (1856), pl. 1.

† Quart. Journ. Geol. Soc. vol. vii. (1851), p. 94.

‡ Proc. Roy. Soc. Edin, vol. vi. (1867), p. 72 &c.