526 Correspondence — Prof. W. M. Davis. 



during Old Bed Sandstone time. Among these conditions, the 

 form of the floor of ancient rocks on which the Old Red lies 

 unconformably may be regarded as of prime importance. 



The problem to which my attention had been attracted is the 

 date and process of origin of the now uplifted peneplain in which 

 the Scotch glens of to-day are carved. Judging by analogy with 

 other peneplains, that of the Scotch Highlands can hardly have 

 been longer exposed to dissection than since the latter part of 

 Mesozoic time ; indeed, Tertiary time alone may have been suffi- 

 cient for the excavation of the narrow glens in the hard rocks 

 of the Highlands, as well as for the more general denudation of 

 the weaker rocks of the Lowlands. It is. therefore, not unreason- 

 able, in my view of the matter, to regard the broad denudation 

 by which the Highland peneplain itself was formed as having 

 been completed in Cretaceous, or, at earliest, in Jurassic time. 

 Whether this denudation was accomplished by marine or by 

 subaerial agencies, or by the co-operation of both, I see no means 

 of deciding definitely ; but, for various general reasons, I incline 

 to ascribe it chiefly to subaerial agencies. 



Now, the reason that my brief footnote afforded material for 

 quotation by Messrs. Macnair and Reid is, that I referred therein 

 to the views of Sir A. Geikie concerning the date of the Highland 

 peneplain, from which I took the liberty of dissenting; but I am 

 at a loss to understand why a quotation from my footnote should 

 be cited as " a very good example of the misconception and general 

 indefiniteness which accompany Sir A. Geikie's description." If 

 the brief note be misconceived and generally indefinite, the blame 

 should fall on no one but myself. 



In continuation, Messrs. Macnair and Reid seem to infuse their 

 own views into my words when the}' say — " Professor Davis speaks 

 of Devonian seas having cut down the Highlands to their base- 

 level." On the contrary, I said that " Devonian erosion consumed 

 a great volume of the contorted and overthrust rocks of the High- 

 lands." Whether this erosion was marine or subaerial, is a difficult 

 matter to decide, and I did not undertake to decide it. That tho 

 erosion of that time reduced the Highlands to base-level, was 

 regarded as probable, but was not directly asserted. 



Moreover, my use of the terms "Devonian" and " Old Red " was 

 as synonyms — not for a moment as names of different times or 

 of successive formations. Furthermore, I said nothing to justify the 

 statement that " Professor Davis speaks ... as if there were two 

 distinct sets of rocks in Scotland, one marine . . . the other 

 fresh-water." The question of the marine or lacustrine deposition 

 of the Old Red (Devonian) was not raised in my note. On the 

 other hand, I cannot justly take shelter under the statement of 

 Messrs. Macnair and Reid that any error in my note "is quite 

 excusable in one who has never studied the rocks of our country, but 

 only read of them in the 'Scenery of Scotland,'" for my reading 

 extends much further; and while I have not "studied" the rocks 

 on the ground, I have at least seen some of them, and in most 

 enjoyable company, from the Buried pre-Torridonian mountains 



