1873.] JTTDD THE SECONDARY ROCKS OF SCOTLAND. 105 



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 Scot- 

 land ; 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 f and Professor Geikie J, 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 main- 

 land, 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 prolon- 

 gation; 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 vol- 

 canic 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 ap- 

 peared to many geologists to be terminated by the palaeontologieal 

 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 ficld-gcologist must bow ; and 

 instead, therefore, of any longer connecting these reptiliferous sand- 

 stones of Elgin and Ross with the Old Bed Sandstone beneath them, 

 I willingly adopt the view established by such fossil evidence, and. 

 consider that these overlying Sandstones and limestones arc of Upper 



* Quart. Jburn. Geol. Soc. vol. xii. (1856), pi. 1. 

 t Quart. Journ. Gcol. Soc. vol. vii. (1851), p. 94. 

 $ Proc. Roy. Soc. Ellin, vol. vi. (1867), p. 72 &c. 



