Prof. C. Lapworth—The Secret of the Highlands. 197 
the fossiliferous Durness-Hriboll series is composed both of two 
members and of three members, and the well-known Durness 
Limestone forms both the central and the highest of these. This 
strangely constituted fossiliferous series is both older and younger 
than the Sutherland gneiss, for it underlies the latter conformably, 
and it overlies it unconformably. 
In all three cases the physical appearances are incontestable and 
admit of no dispute. It is needless to point out to the youngest 
tyro in geological field-work that we have here a complete strati- 
graphical dead-lock. It is impossible to reconcile these conflicting 
results as they stand. If no stratigraphical principles additional to 
those enunciated above are to be permitted in this discussion, the 
N.W. Highland controversy, which has already lasted for one gene- 
ration, may well last for another, to divide and embitter geological 
investigators, and bar the way to those higher and more important 
geological problems that await solution. 
Now in this Durness-Eriboll region the physical geologist, pure 
and simple, isin his own element. There are, practically, no fossils to 
complicate matters: the successive recognizable formations are totally 
distinct in petrological character, and the evidences of superposition 
are complete and unequivocal. And yet with all these advantages 
the accepted methods of British Lowland stratigraphy utterly break 
down. They land us in a set of conclusions so unnatural and absurd, 
that it would be ridiculous to suppose that any scientific man could 
entertain them for a moment. ' 
Here, then, I reach from the purely physical side, precisely the 
same point I attained several years ago largely from the paleonto- 
logical side: viz. the ordinary broad rules of British stratigraphy 
enumerated above, as applied to gently inclined strata, do not of 
themselves afford irrefragable evidence of sequence among the greatly 
convoluted older rocks when the latter are regarded as grouped in 
broad masses, and conclusions founded solely upon the testimony 
they afford under these circumstances are practically valueless. 
In this desperate extremity, it may be suspected that our physical 
geologists will be tempted to look a little more closely into the 
matter, and see if a more detailed study of these rocks in the light 
of the discoveries made of late years in mountain regions will aid 
us in clearing up the difficulty. 
In the following sections I have shortly summarized some of those 
more important points in the stratigraphy of convoluted rocks 
which bear upon the present question. For the sake of simplicity 
of treatment, I have merely investigated here that simplest hypo- 
thetical case in which the mountain strata are comparatively homo- 
geneous, have been subjected to opposing pressures acting along 
parallel lines, and have consequently been looped up into symmetrical 
folds of infinite length. In order to avoid prejudicing my case, Lhave, 
where possible, selected my illustrations from standard authorities, 
especially from the classical work of Professor Heim. 
