196 Prof. C. Lapworth—The Secret of the Highlands. 
of their application to the investigation of the geology of the Dur- 
ness-Hriboll region. 
(1.) When they are applied in the usual manner to the section of the 
region as a whole (see Fig. 1, Plate V.), they appear to demonstrate 
that the unaltered Durness-Hriboll series is older than the generally 
metamorphic Sutherland series, and that it is strictly conformable to 
the latter; the Durness-Hriboll Limestone forming the central member 
of the unaltered series, and graduating upwards through the Upper 
Quartzite and a massive group of ‘“‘igneous rocks” into the typical 
altered rocks of the Sutherland series. 
(2.) When they are applied to the most important sections in the 
Durness area? (see Figs. 2 and 3), they apparently demonstrate that 
there is no intervening igneous group lying between the conformable 
Durness and Sutherland series, but merely a thin seam of flaggy 
quartzite, which is only locally present. 
(3.) When they are applied to the most easily interpreted section 
in the Loch Eriboll district, they apparently demonstrate that the 
unaltered Durness-Eriboll series, of which the Durness-Eriboll Lime- 
stone is the highest member, is younger than the generally meta- 
morphic Sutherland series, overlying the latter with marked 
unconformability (see Fig. 5). re 
In brief, if these rules are to be our sole guides, it follows that 
2 As it has been suggested that the fossiliferous limestone of Durness is distinct 
from the generally non-fossiliferous limestone of Kriboll, from the fact that the two 
have ‘‘an absolute difference of composition’? (Dr. Heddle, Mineralogical Magazine, 
1881, p. 316); the limestone of the Eriboll-Kishorn line being throughout its 
whole range in the county ‘‘a very typical dolomite,’’ while the Durness rock is a 
“fairly pure limestone ;’’ I beg to submit the following analyses of four specimens 
of the Durness rock, collected by myself at the four localities named in the appended 
list. They may be looked upon as affording a fair idea of the chemical composition 
of the Durness beds, as they are traversed from west to east upon the ground. The 
specimens were analysed for me in the Chemical Laboratory of the Mason College, 
under the kindly personal superintendence of my colleague Dr. W. A. Tilden, F.R.S. 
From these analyses it would appear that while some of the zones of the Durness 
Limestone contain but a small proportion of magnesian carbonate, and may be 
defined as ‘‘ fairly pure limestone,” yet many of the beds, like those of Eriboll and 
Assynt band, are unquestionably dolomitic. The composition of the rock occurring 
in that special Durness zone, which, according to my own view, is repeated again and 
again in the Eriboll-Assynt area, is given in the last of these analyses, and this is 
clearly that of ‘‘ a very typical dolomite.” 
ANALYSES OF SPECIMENS OF Durness LIMESTONE. 
2 (292) ep. (281) c. (363) d. (385) 
Cady. inte 96-27 65-60 52°94 54°12 
Mol Dahir dstecsiee 1-40 26°20 43°71 45°90 
Insolitble 25. <susese 2°01 6°85 2°43 trace 
Pe rian euapevdeve ts ? ¥ P p 
99°68 98-65 99°08 100-02 
(2.) Specimen 292, from Kiland-Dhu, on Kyle of Durness. 
(.) Specimen 281, from hills near Loch Borralann. 
(c.) Specimen 363, from near fossil-bed. Balnakiel. 
(d.) Specimen 335, from cliffs between Sango-bay and Smoo Cave. 
