Prof. C. Lapworth—The Secret of the Highlands. 123 
(a) A Lower or fossiliferous (Durness) division, composed of 
1. Lower Quartzite and flaggy fucoid beds of Kyle of Durness, 
and west side of Loch Hriboll. 
2. Limestone of Durness, with Maclurea (regarded as the equiva- 
lent of the non-fossiliferous limestone of Eriboll). 
3. Upper Quartzite of east side of Loch Eriboll. 
This lower division graduates upwards as a whole insensibly 
into the 
(b) Upper or Metamorphic division of the Flaggy gneisses and 
schists of Fair Head and Ben Hope (Sutherland series or Flaggy 
gneiss). 
2.—Theory of Professor Nicol. 
Murchison’s view of the superposition of the Sutherland gneisses 
and schists to the Durness series was strongly opposed by the late 
Professor Nicol, who held that the (A) Archean or Hebridian of 
Fashven and Ben Cannabin was covered unconformably by the 
(B) Paleozoic strata of Durness and Hriboll, in which he recognized 
only three members— 
1. The Lower Quartzite. 
2. The Fucoid beds. 
3. The Durness or Eriboll Limestone. 
He held that the so-called Upper Quartzite of Murchison was merely 
the Lower Quartzite repeated by inversion, and that it was newer 
than the Sutherland gneissic series. The latter he held to be, upon 
the whole, an ancient metamorphic Pre-Cambrian gneiss brought 
up to the eastward of Loch EHriboll by a gigantic overthrow fault : 
running generally along a line of syenite or intrusive igneous rock, 
which occurred in occasional patches along the fault line from Whiten 
Head to Loch Maree.? 
3.—Theory of Professor Heddle. 
Founding mainly upon the fact that the Assynt-Eriboll, or easterly 
band of the Quartzite and Limestone series, is unfossiliferous, and 
that its most prominent bed to the south is dolomitic, while the 
Durness Limestone is fossiliferous, and its beds are not dolomitic, 
Professor Heddle agrees with Murchison in regarding the apparent 
ascending succession, from the basement quartzite of Ben Cannabin 
into the Sutherland schists, as the true one; the ‘“‘ igneous rocks ” 
being interbedded, and not destroying the general continuity of the 
sequence. He differs from Murchison, however, in placing the 
whole in the Archean, with the exception of the fossiliferous Durness 
Limestone, which he believes is merely an isolated fragment of an 
originally overlying Paleozoic formation dropped in by faults.’ 
4.—Theory of Dr. Chas. Callaway. 
According to Dr. Callaway also, there are probably two distinct 
Archsean series in the region, (a) the massive Hebridian gneiss at 
1 Quart. Journ. Geol. Soc. 1856, p. 17, et seq. 
2 Heddle, Microscopical Magazine, 1881-82. 
