Prof. C. Lapworth—The Secret of the Highlands. 195 
thrown upon some of the more obscure points in my study of the 
Durness-Eriboll district is so clear and vivid, that they fall most 
naturally into this place. Many of the points discussed in the 
following paragraphs (Pars. ix. and x.) will be found in the truly 
magnificent work of Professor Heim’ upon the convoluted rocks . 
of the Alps. For those not hitherto published, I hold myself 
responsible. The latter therefore are the only points open to the 
objection of being original or heterodox, and the attempt here 
made to summarize a few of the more essential principles of moun- 
tain stratigraphy, and to apply them to the investigation of the 
Highland region, may be, perhaps, received as a first essay in one 
of the most difficult and obscure departments of British geology. 
But, before these principles can be introduced into this discussion, 
it will be necessary to demonstrate the inadequacy of the ordinary 
methods of stratigraphy as applied to the rocks of the N.W. 
Highlands; for, like the Upper Paleeozoic and Neozoic strata, these 
rocks are often very gently inclined, dipping at angles varying from 
60° to 30°, and sometimes as low as 10° or even 5°. 
VIII.—Application of the ordinary rules of British Lowland Strati- 
graphy to. the study of the Durness-Eriboll Formations. 
The chief rules of British stratigraphy as applied to gently 
inclined rock-formations, which bear upon our present subject, may 
be thus shortly defined. 
(a) 'T'wo successive series of gently inclined strata agreeing essen- 
tially in dip, strike, and apparent amount of convolution, are con- 
formable to each other, and of these two conformable series, the 
physically overlying series is necessarily the younger. 
(b) When the basal bed of a conformable series of strata rests 
immediately upon the surface of an underlying and discordant series, 
and contains included fragments of that underlying series, the two 
series are unconformable to each other, and the underlying series is 
necessarily the older. 
(c) Faults or dislocations in gently inclined formations are normally 
right lined, and the plane of fracture normally hades or inclines in 
that direction in which the rocks have been depressed. 
These are almost the only fundamental stratigraphical rules which 
have hitherto been employed in common by all parties in the study 
of the N. W. Highland succession. By the aid of the diagrams upon 
Plate V. and the descriptions given in the earlier paragraphs of the 
present paper,’ the reader may easily gather for himself the results 
* Mechanismus der Gebirgsbildung, A. Heim, Zurich, 1878. 
* I have to apologize for ‘the following errata in the previous part of this memoir : 
p- 122, line 1, for north-west, read north-east. 
p. 123, par. 3, line 10, for placing the whole in the Archean, read regards 
the Silurian age of the Sutherland gneiss as open to doubt. 
p- 123, bottom line, for Microscopical Magazine, read Mineralogical Magazine, 
1879, p. 137; 1881, p. 322; 1882, No. 22, p. 6. 
p- 126, line 7, for Hielem, mead Heilim. 
p- 127, line 13, for VI. d. read IV. 0. 
oe lime-2 05 for Die readilane: 
»  lne 23, for II. d. read I. 6. 
