P. Macnair 8f J. Reid — On the Old Red of Scotland. 113 



denudation, commencing in Upper Silurian times and lasting all 

 through the long period of the Lower Old Red Sandstone age. It is 

 evident from a consideration of these Upper Silurian and Lower Old 

 Red Sandstone deposits that the old Palaeozoic mountain chain was 

 gradually sinking along its flanks, and that the sea, slowly 

 advancing upon this sinking land, laid down these deposits, the 

 first and lowest of which we see in the south of Lanarkshire, and 

 the highest and latest in the topmost beds of the Lower Old Red 

 Sandstone as developed in Caithness. It has generally been believed 

 that all the stratigraphical evidence has been in favour of these 

 separate areas of Old Red Sandstone being also separate basins of 

 deposit, hut it will be found that however difficult it may be to 

 explain the exact condition under which these rocks were ac- 

 cumulated, one thing is certainly evident, and that is that they were 

 not deposited in isolated basins as maintained by Godwin-Austen, 

 Ramsay, and Geikie. 



In Sir Archibald Geikie's "Scenery of Scotland" 1 will be found 

 the most detailed work that has yet been done with regard to the 

 physical evolution of our country, the opinions contained in it 

 being those generally accepted and followed by present-day 

 geologists. Referring to the second edition of that work at p. 137 

 on the chapter dealing with the tableland of the Highlands, he says : 

 "The long flat surfaces of the Highland ridges cut across the edges 

 of the vertical strata mark, I believe? fragments of a former base 

 level of erosion ; in other words, they repi'esent the general sub- 

 marine level to which the Highland region was reduced after 



protracted exposure to subaerial and marine denudation 



And in this rolling plain we should find a restoration of the bottom 

 of a very ancient sea." He further goes on to say : " The first fact 

 which a study of the topographical features and geological structure 

 of the Highlands establishes is, that the ancient land formed after 

 the stupendous movements that gave the rocks of the region 

 their present character was worn down by prolonged denu- 

 dation. Its mountains were levelled, its valleys were planed down, 

 and finally the region was reduced to a base level of erosion beneath 

 the waves either of a group of great lakes or of the sea." 



Let us now examine more carefully, and in greater detail, these 

 statements of Sir Archibald Geikie. The latter part of the para- 

 graph just quoted seems to us to indicate in a few words the rather 

 indefinite idea which Sir Archibald Geikie gives in his "Geology 

 and Scenery of Scotland " of one of the most important points in the 

 physical evolution of our country. He says that the old crystal- 

 line or metamorphosed Lower Silurians were reduced to a base- 

 level of erosion, beneath the waves, either of a group of great 

 lakes or of the sea. Sometimes in the course of this chapter, we 

 would think it was the sea. For instance, as in the sentence just 

 quoted, where he says, " In this rolling plain we should find a 

 restoration of the bottom of a very ancient sea." Again, in a few 



1 " Scenery of Scotland," 1st and 2nd editions, under the heading ' Tableland of 

 the Highland's.' 



DECADE IV. VOL. III. — NO. III. 8 



