116 P. Macnair 8f J. RHd—On the Old Red of Scot land. 



Pre-Cambrian and Old Bed Sandstone deposits, their origin is not, 

 we believe, to be sought for in any lacustrine deposit, as has been 

 maintained by Ramsay, Geikie, and Hull. They are rather types 

 of a great series of shore deposits gradually accumulating along the 

 margin of a slowly sinking continental area, which in its upper 

 regions is rapidly undergoing subaerial denudation. This type of 

 deposit it not uncommon all through the geological scale, and to it 

 we believe the Old Red Sandstone conglomerates of Scotland belong. 

 Prof. Bonney 1 makes interesting remarks upon this point in his 

 address to the British Association in 1886. He there says that 

 " Pebbles indicate the action of the waves of the sea or 

 of strong currents, marine or flnviatile." Further he continues: 

 " The waves of lakes have also some rounding effect, but this, 

 except in the case of very large lakes such as Lake Superior, is not 

 important, and such cases are, of course, not of common occurrence." 

 As we have already pointed out, the massive conglomerates of such 

 a small basin as we are led to believe Lake Lome must have been, 

 and, what is still further in evidence, the much smaller basins that 

 are alleged to have existed on the separating ridge between Lake 

 Caledonia and Lake Orcadie, entirety preclude, even from a peno- 

 logical point of view alone, the possibility of their being other than 

 outliers from the main mass. The whole penological aspect of the 

 Old Bed Sandstone rocks, as seen in Scotland, is, of course, highly 

 indicative of their littoral origin ; the entire absence of any of the 

 deeper oceanic types of sedimentation, such as shales and limestone, 

 also confirming this view. The rocks as seen in Caithness, Forfar- 

 shire, and Perthshire, and generally in the valley of Strathmore, 

 mainly consist of great beds of grey and red sandstone, with 

 occasionally local deposits of conglomerate, the great feature of the 

 whole being their characteristic red colour. Now we think that this 

 red colour, due to the presence of the red oxide of iron in the rocks, 

 cannot be fairly claimed as an argument for the fresh-water origin of 

 these deposits. Prof. Gosselet has shown that in the Devonian basin 

 of Dinant, the same beds are in one part red and barren of organic 

 remains, and in another part of the same area are of the usual 

 colour and are full of marine fossils. With Sir Charles Lyell 2 we 

 ask the question. Why should shells and corals be generally wanting 

 in all sedimentary rocks, the colour of which is determined by the 

 red oxide of iron? and we believe that the answer cannot lie in 

 the assertion that they are all fresh-water deposils, seeing that even 

 in such undoubted marine deposits as the Devonian, Carboniferous, 

 and Permian formations, it is common in the ordinary beds to find 

 corals and shells, while those coloured with peroxide of iron are en- 

 tirely barren of organic remains. The solution of the problem rather 

 lies in the fact that the presence of peroxide of iron in these rocks 

 is inimical to the preservation of fossils with a calcareous test, 

 and that more especially in the case of sandstones, which even when 

 composed of pure silica are well known to be a bad medium for the 

 pi'eservation of molluscan and other similar organic remains. 



1 British Assoc. Report, 1886. 2 " Elements of Geology," 3rd edition, p. 43o. 





