108 P. Macnair 8f J. Reid—On the Old Red of Scotland, 



these deposits. We propose to discuss the various points in the 

 following order: first, 1 lie early Pal»ozoio mountain chain, in 

 which we will give a resume of what, is known of that old continent 

 upon which the later Palaeozoic rocks were deposited as a nucleus ; 

 second, we will consider the general, physical, and strut igraphical 

 evidence in favour of the marine and continuously ascending order 

 of these deposits in Scotland through a lower, middle, and upper 

 series. Under the division of the penological consideration we will 

 discuss those questions relating to the conditions under which these 

 rocks were deposited, the almost universal presence of peroxide of 

 iron in the rocks and their consequent barrenness of molluscan 

 remains, and finally the palaeontological evidence in favour of 

 a marine origin for the organisms found in these deposits. We 

 also in the course of the paper propose to show the " Character of 

 the Strata " is entirely against its supposed deposition in small 

 inland fresh-water lakes ; that the absence of unequivocally marine 

 fossils is not so complete as supposed, neither is it fatal to their 

 marine origin; that land plants occur freely in undoubted marine 

 strata ; and that the existence of the representatives of ganoid fishes 

 in the rivers and lakes of the present day is entirely out of evidence 

 when we consider the immense number of these fossil fishes found 

 in undoubted marine deposits both in England and Russia, and of 

 their wide distribution over the continents of Europe and America. 



II. The Early Paleozoic Mountain Chain. 



Before passing on to discuss the physical, petrological, and palae- 

 ontological evidence in favour of a marine origin for the Old Red 

 Sandstone of Scotland, it would be here useful to give a brief 

 recapitulation of the physical conditions of our country prior to 

 the deposition of these later Palaeozoic deposits. It is generally 

 believed that in early Palaeozoic time the main land mass must have 

 lain somewhat to the north-west of the present continent of Europe, 

 and may have partly existed in what is now the deep basin of the 

 Atlantic. The old Archaean gneiss of the islands and northern 

 Highlands seems to represent part of the primitive core round 

 which the later Palaeozoic rocks were accumulated. We do not now 

 propose to discuss these early Palaeozoic rocks, but to us those 

 massive red sandstones and conglomerates of Loch Torridon only 

 shadow forth the same physical processes that were at work in the 

 still later Old Red Sandstone age ; lying as they do upon the older 

 Archaean rocks, they are the undoubted littoral accumulations along 

 that ancient coast-line which are invariably seen to accompany 

 a great period of mountain-building, indicating that a rapid process 

 of subaerial denudation must have been at work in the higher 

 regions, the detritus being swept out through the old river courses 

 and subsequently rearranged along the shore line by the action of the 

 sea. But to this point we propose to return later on. Immediately 

 on the top of these Torridon sandstones and conglomerates, and 

 separated by a strong unconformability, we find a great series of 

 metamorphosed rocks of Cambrian, Ordovician, and Silurian age, 



