112 P. Macnair 8f J. Br id— On the Old Red of Scotland. 



Subsequent to this, the midland valley was depressed between the 

 powerful trough-faults; tbe upturned edges at the south showing 

 Silurian types, and to the north, those of Old Red Sandstone 

 times. Had these rocks been deposited in a basin, we should 

 have expected the strata to be more or less homologous on each 

 side of the basin; but this, as we have shown, is decidedly not the 

 case. Jukes-Browne, 1 in his " Building of the British Isles," makes 

 some very pertinent remarks upon this subject. He says : " From 

 the proofs which have been adduced of the original wide extension 

 of the Old Red Sandstone, it might be thought that the three 

 principal basins could hardly have been separate lakes, but must 

 have been inlets proceeding from one large inland sea, the gi'eater 

 part of which lay to tbe east of Scotland." And, indeed, so far as 

 the stratigraphical evidence goes, this would be tbe most natural 

 conclusion, for the lithological differences between the strata of 

 the several basins are hardly greater than the differences which 

 exist between the Lanark and Forfar types in the Caledonian basin. 

 The paleeontological differences are, however, very much greater ; 

 the piscine fauna of the Forfar and Caithness flags being so distinct, 

 that Sir R. Murchison thought they could not be of the same age, 

 and was led to suggest that the Caithness flags formed a middle 

 group distinct from the Lower Old Red, and of younger date than 

 the flags of Arbroath, in Forfarshire. Further on, he says, there is 

 less evidence for regarding the Cheviot basin as distinct from the 

 Caledonian, as no fish have yet been found in the Cheviot district, 

 and we do not know how far the Lower Old Red original^ 

 stretched over the southern uplands. We have lately been examining 

 the Lome basin, and nothing will persuade us that it is other 

 than an outlier removed and preserved from the main mass by the 

 effects of some powerful faults. The presence of such extremely 

 large boulders in its massive conglomerates as that seen in the base 

 of the well-known Dog-stone of Dunnoly, entirely precludes the 

 possibility of its being formed in a basin only a few miles wide. 

 The stratigraphical evidence from the volcanic phenomena we also 

 consider is strongly against the basin origin of these deposits ; for 

 instance, a great mass of volcanic rock forming the Sidlaws and 

 Oehil hills is found interbedded with the sediments of the so-called 

 Lake Caledonia basin, at a height of several thousand feet above 

 the base. Now in the whole of the 16,000 feet of Lake Orcadie 

 this volcanic zone is entirely absent, which. I think, points to the 

 fact that these two basins could not have been contemporaneous, 

 for had that been so, further evidence of this extensive volcanic 

 activity would have been found in Lake Orcadie when we consider 

 the narrowness of the ridge that must have separated the two basins. 

 The process which metamorphosed and plicated these lower 

 Palseozoic rocks into a true mountain chain also upheaved them 

 above the general level of the surrounding sea. when they im- 

 mediately became the prey of the subaerial denuding agents. Then 

 followed a long and intense period of subaerial and marine 

 1 " Building of the British Isles," p. 61. 



