1873.] JTJDD THE SECONDARY ROCKS OF SCOTLAND. 145 



argued by Professor Ramsay, Mr. Godwin-Austen and others), of 

 lacustrine origin, — a conclusion supported by the paucity of organic 

 remains in them, and the peculiar characters of the rock which forms 

 their upper member. 



§ 2. The Rhcetic ? 



At the base of the Liassic series of strata in Sutherland, and imme- 

 diately overlying the formation just described, there occurs a series 

 of coarse sandstones with beds of conglomerate (fig. 14, c, page 143). 

 As has been already pointed out, the pebbles in this conglomerate 

 are not derived from the Old Red Sandstone or any other Palaeozoic 

 rock, but in part at least, from the sandstones and cherty lime- 

 stones of the Trias. The base of the Lias in Scotland, as in South 

 Wales and many parts of France and Germany, is usually formed by 

 similar conglomerates ; but on the Western Coast the Secondary 

 rocks generally repose unconformably on the older Palaeozoic strata, 

 such as the Silurian and Cambrian, and the conglomerates are made 

 up of pebbles of those rocks. 



These conglomerates and sandstones of Sutherland, which attain 

 a considerable thickness, but are somewhat imperfectly exposed, 

 have not exhibited any trace of those bone-beds sometimes found in 

 equivalent strata ; nor, indeed, have they yielded any kind of fossil 

 remains whatever. As indicating the slight oscillations of level, 

 insufficient to produce unconformity, which marked the gradual 

 transition from the Trias to the Lias, we may, with a strong show of 

 probability, consider them to be of Rhaetic age. They are evidently 

 a littoral deposit, and are overlain by, and graduate up into the series 

 of estuarine strata constituting the base of the Lower Lias. 



On the opposite or southern side of the Moray Pirth there are a 

 number of masses of strata, not in situ, but included in the Boulder- 

 clay, which from their mineral characters have been variously re- 

 ferred by different authors to the Wealden, Purbeck, and Rhaetic. 

 I have already pointed out how little weight should be attached to 

 mere mineral characters in the determination of the age of the 

 Secondary strata of Scotland ; and as the masses in question are 

 completely isolated in the drift, we are reduced to the purely palaeon- 

 tological evidence. 



The most important of these masses is that of Linksfield, which 

 was first brought under the notice of geologists by Dr. Gordon in 

 1832*. The peculiarities of the strata here were found by Dr. 

 Malcolmson to be such as to lead him, in the year 1838 f, to suggest 

 that they were the equivalents of the Wealden or Purbeck — a view 

 that was adopted by Mr. Duff, Mr. Robertson and other observers J. 

 On the other hand, Mr. C. Moore §, in the year 1859, pointed out the 

 striking resemblances in the mineral characters and succession of 



* Proc. Geol. Soc. vol. i. p. 394. t Ibid. vol. ii. p. 667. 



J Sketch of the Geology of Moray, 1842 ; Anderson's ' Guide to the High- 

 lands,' 3rd edition (1851) ; &c. 



§ Brit. Assoc. Eept. (1859) p. 264. Quart. Journ. Geol. Soc. vol. xvi (1860) 

 p. 445. 



VOL. XXIX. PART I. L 



