122 Prof. C. Lapworth—The Secret of the Highlands. 
west and south-west, or at right angles to the direction of the under- 
lying gneiss. This higher formation appears to be composed of 
two very distinct divisions, viz. :— | 
1. A Lower division of quartzites, flazgy beds, and limestones, 
often greatly hardened, but the calcareous beds of the division 
(Durness Limestone) afford Maclurea, Murchisonia, Orthoceras, and 
other recognizable Lower Paleeozoic fossils. (This division may be 
termed the Durness or Eriboll series.) 
2. This Durness-Eriboll series appears to be surmounted con- 
formably by an Upper division of flaggy, quartzose, micaceous and 
chloritic schists, with thick zones of hornblendic and micaceous 
flaggy gneisses and bands of so-called igneous rock (dioritic or 
syenitic rock of some authors). This division forms the well-known 
Upper Gneiss, or Sutherland Flaggy Schist series. 
As regards the superiority of the fossiliferous Durness-Hriboll 
series (B. 1) to the basal Hebridian or Hornblendic gneiss, there 
has never been any dispute. But the true relation of the Suther- 
land series or so-called Upper Gneiss (B. 2) to the fossil-bearing 
rocks is not yet settled, after years of the keenest controversy. This 
Sutherland series not only contains beds hardly more altered than 
those of the fossiliferous Durness-Hriboll series, but it includes also 
hornblendic and micaceous gneisses almost inseparable mineralogi- 
cally from those of the basal Hebridian. It stretches too, in almost 
unbroken mass, eastward and southward from this region over the 
entire area of the Central Highlands, where it covers at least an 
area of 15,000 square miles,! and has not yet afforded a trace of a 
recognizable fossil. Many geologists, therefore, aware that the con- 
cession of the superiority of the Sutherland series to that of Durness, 
carried with it, almost of necessity, the admission of the Paleozoic 
age of all the schists and gneisses of the Central Highlands, have 
refused to pin their faith to the apparent stratigraphy, and have 
sought to explain it upon the hypotheses of hidden faults, or folds, 
or stupendous overthrows of the strata. Others, again, have boldly 
accepted the visible sequence as it stands, with all its awkward 
consequences. It is hardly necessary perhaps to point out that the 
latter view, being the most superficial and the most natural, is that 
which has hitherto been the most orthodox and the most popular. 
II.—Theories of the Physical Structure of the Durness-Eriboll Region :— 
At least four distinct theories have been already published in 
explanation of the Durness-Hriboll section. 
1.—Theory of Sir Roderick Murchison. 
According to Sir Roderick Murchison, the succession in this region 
is composed of two distinct rock systems, viz. ? 
(A) Archean or Laurentian: composed of the basal Lewisian or 
Hebridian, hornblendic gneiss of Fashven and Ben Cannabin: a 
true crystalline gneiss with a steep dip and N.W. strike. 
(B) Paleozoic or Silurian, consisting in ascending order of :— 
1 Geikie, Handbook of Geology, 1882, p. 584. 
2 Quart. Journ. Geol. Soc. August, 1859. 
