P. Macnair 8f J. Reid — On the Old Red of Scotland. 107 



hand the evidence which is in favour of its entire extension over 

 Scotland, and of its marine origin, has either been entirely overlooked 

 or so minimized as not to be taken at its real value. 



The first discoverers and workers amongst these rocks, Hugh 

 Miller and Sir Roderick Murchison, firmly believed in its marine 

 origin, and though Hugh Miller was not so much of a stratigrapher 

 as a palaeontologist, yet he clearly realized the fact that the Old Red 

 Sandstone must have at one time covered the whole of the Scottish 

 Highlands, as in his " Old Red Sandstone "' he speaks of a sea that 

 extended from Ben Lomond to the maiden paps of Caithness. Sir 

 Roderick Murchison, on the other hand, entered into a detailed study 

 of its stratigraphical and physical structure and relationship, and it 

 is mainly to his views we are persuaded the students of the Old Red 

 Sandstone rocks of Scotland must finally return. 



Stratigraphically, Murchison divided the Old Red Sandstone rocks 

 of Scotland into three members — the upper, the middle, and the 

 lower, each characterized by a distinctive fauna : — the lower group, 

 as seen in Scotland, being principally developed in Forfarshire 

 and Perthshire, and characterized by Cephalaspis and Pterygotus ; 

 the middle group, seen in Caithness, and containing Dipterns, 

 Osteolepis, etc. ; while the third or upper group, well developed in 

 Dura Den, and containing Holoptychius and other characteristic 

 forms, passes up conformably into the basement beds of the Carbon- 

 iferous formation, there being always a decided break between the 

 upper member and all the older rocks. He also correlated the Scottish 

 Old Red Sandstone with its deep-water equivalent, the Devonian 

 of England and Russia, pointing out that in the latter country the 

 Devonian rocks containing marine shells were also interstratified 

 with red sandstones, in which no shells wei'e found, but which were 

 replete with the piscine fauna common to the Scottish rocks. 



Latterly, however, and principally through the work of Godwin- 

 Austen, Ramsay, and more particularly Sir Archibald Geikie, 2 the 

 Old Red Sandstone of Scotland came to be looked upon as a fresh- 

 water deposit accumulated in isolated basins. The researches of 

 the two first writers were principally directed to the petrological 

 characters of the rocks. The latter was the first to isolate the 

 Scottish areas of Old Red Sandstone into separate basins of deposit, 

 with the distinctive names Lake Orcadie, Lake Caledonia, Lake 

 Lome, and Lake Cheviot. He believes they were all contemporaneous, 

 doing away with the existence of the Caithness rocks as a middle 

 group, and explaining the discrepancy of their fossil contents on 

 the grounds that they are no greater than those of contiguous 

 fresh-water basins at the present day. In his " Scenery of Scotland " 

 he also presents some of the physical problems connected with the 

 Old Red Sandstone; consequently it is mainly to the statements of 

 Sir Archibald Geikie we now propose to revert, as being the 

 principal authority for the isolated lake and fresh-water origin of 



1 " Old Red Sandstone," 7th edition, p. 53. 



2 See ""The Old Red Sandstone of Western Europe"— Trans. Roy. Soc. of 

 Edinburgh, vol. xxviii ; and "Text Book of Geology." 



