

P. Macnair 8f J. End — On the Old Red of Scotland. 109 



forming the main mass of the Scottish Highlands. In the inter- 

 vening period which elapsed between the deposition of the lowest 

 member of this group and the highest, the whole series of beds 

 were subjected to a great process of upheaval into a mountain 

 chain of elevation. It seems to have received its maximum of 

 corrugation and plication in that difficult and complex area in the 

 north-west of Sutherlandshire. Receding to the south-east we find 

 the curving of the beds become more and more gentle till they 

 reach the comparatively unaltered rocks of the southern uplands. 

 The great mass of this mountain chain, then, must have lain to the 

 north-west of the present Old Red Sandstone area, and we now 

 proceed to show how after this long period of upheaval the 

 mountain mass once more began to sink below the level of the sea, 

 and that gradually the waters of the Old Red Sandstone sea 

 levelled it down to the very core. 



III. Physical and Stra.tigraphical Considerations. 



We now pass on to notice some of the physical and stratigraphical 

 aspects of the matter. A consideration of the deposits lying immediately 

 upon the metamorphosed rocks which then formed land leads us to 

 the conclusion that the whole of this continental area must have been 

 in a gradually sinking condition, and that these huge masses of con- 

 glomerate, lying at the local base of the Lower Old Red Sandstone 

 wherever the latter is exposed, point unmistakably to the existence 

 of a great series of unstable sea margins, slowly creeping back- 

 wards upon the main mass of the gradually sinking land. Along 

 the flanks of the Grampians, and now exposed by a powerful fault, 

 we have a great mass of conglomerate, consisting in some cases of 

 boulders nearly six feet long. The conglomerates range across the 

 country from shore to shore ; in some cases north of the line of fault 

 we have these conglomerates still occupying their normal position 

 upon the older schists and grits. If the effect of this fault were 

 undone, and these conglomerates were raised to their original 

 position, they would stretch far over the Grampians along with the 

 higher deposits of sandstones and their fish remains, which now 

 occupy the central valley of Strathmore. The following diagram, 

 drawn to scale, will show this very clearly (see p. 110). 



The dark part of the section to the north represents the present 

 elevation of the Highlands above the level of the sea drawn to scale, 

 and culminating in Ben Muich Dhui. To the south of the line of 

 fault are shown the massive beds of Old Red Sandstone con- 

 glomerates dipping at high angles to the south-east, and estimated 

 to be about 20,000 feet in thickness, about four times the present 

 height of Ben Muich Dhui. At the point A, immediately to the 

 north of the line of fault, and resting directly upon the old 

 crystalline schists, are often to be found patches of the basal con- 

 glomerate of the Lower Old Red Sandstone still occupying its 

 normal and unaltered position, so that if the effect of the great fault 

 were undone, and the whole Old Red Sandstone deposits of Strath- 

 more were upraised to their original position, they would overlook 



