Correspondence — Prof. W. M. Davis. 527 



on the shore of Loch Maree to the Carboniferous rocks of the 

 Lowlands. But from these personal matters, let me turn again 

 to the problem of the Highland peneplain. 



It seems to me beyond dispute tbat a great denudation (whether 

 marine or subaerial is here irrelevant) preceded the deposition of the 

 Old Red (Devonian), because its lowest strata are strongly uncon- 

 formable on their foundation. The place where the detritus furnished 

 by this denudation was deposited is unknown ; but this does not 

 weaken the evidence of the denudation. The precise date of the 

 denudation is not defined ; it certainly pi'eceded the deposition 

 of the Old Red, but its chief accomplishment may have been at 

 a considerably earlier date ; indeed, after the greater part of the 

 denudation had been effected, there may have been some deformation; 

 and upon this deformed denuded surface, the Old Red deposition may 

 have been begun. This can only be told by piecing together such 

 fragments of the Old Red floor as are now in sight, restoring them 

 to the position that they had at the beginning of Old Red deposition 

 by allowing for the dip that the Old Red strata have since then 

 gained, and then judging as well as may be whether the restored 

 floor has the form of a surface of denudation or of deformation. 

 Likely enough, this problem is not definitely soluble ; but as far 

 as I have read, the facts fully support the general statement that 

 "a vast denudation was accomplished in earlier times than the Old 

 Red Sandstone period." The contention that there was no such vast 

 denudation does not seem to me well grounded. On the other hand, 

 it seems equally indefensible to maintain that the surface produced 

 by the very ancient pre-Old Red denudation is essentially identical 

 with the once continuous peneplain of the Highland ridge-tops. 

 Whatever even floor was produced before the beginning of Old Red 

 deposition, it must be altogether lost to our sight by the significant 

 deformation and the extensive denudation which have taken place 

 since. 



At the close of the Old Red period, some old-land areas may 

 have remained above water (marine or lacustrine is immaterial in 

 this connection). Around any such areas stretched the horizontal 

 Old Red strata. But that condition is not presented to us ; for 

 the Old Red strata were at some later time more or less tilted, 

 especially around the Grampians ; and in this disturbance the 

 foundation rocks must have shared with their cover. It is true 

 that in certain districts the Old Reds have been little disturbed ; 

 but the dips that I have seen in the neighbourhood of Moray Firth 

 are quite sufficient to have required a significant disturbance in the 

 old-land floor, as well as in the Old Red cover. Hence it seems 

 impossible to make the peneplain that is indicated by the existing 

 ridge-tops of the Highlands agree with either the pre-Old Red 

 floor, or with the old-land areas that may have remained above 

 water at the end of Old Red deposition. Just what view Messrs. 

 Macnair and Reid hold on this question I do not gather from their 

 essay ; but my reasons for differing from Sir A. Geikie do not seem 

 to me to exhibit misconception or general indefiniteness. 



Whatever peneplain is recognizable in the sky - line of the 



