15 
product of stresses incident to increased volume of the beds resulting from 
their change from anhydrite to gypsum. One of these local anticlines on 
the south bank forms a gothic arch of remarkable beauty and symmetry 
rising about 25 feet above the level of the river. At many points the 
stresses to which these beds have been subjected have produced a breccia. 
The entire face of the cliffs shows at such localities a mass of angular 
limestone boulders of various sizes firmly cemented together in a calcareous 
matrix. The appearance of the breccia is shown in Plate I, figure 1. 
Between these vertical belts of crushed beds lie sections in which the 
strata often remain horizontal and undisturbed (Plate II, figure 1), The 
anhydrite and gypsum which locally form boulderlike masses are shown 
on Plate I, figure 2. The following section is exposed on the south side 
of the island near the north bank of the river at the upper end of the 
cliffs. 
Section at the Upper End of the Cliffs 
Feet 
(a) Thin-bedded, drab, slightly magnesian limestone . . 10± 
(b) Whit© and cream-coloured anhydrite and gypsum in thin, horizontal, ribbon-like 
bands 50± 
(c) White gypsum and anhydrite 6 
Only the uppermost beds of this section appear to contain fossils, and 
these very sparingly. None has been found in the lower part of the 
section. The specimens collected have been listed as follows: 
Spirif&r crispus (Hisinger) 
Modiolopsis sp. 
Modiolopsis sp. cf. ortkonota (Conrad j 
This fauna represents a late Silurian horizon, probably the approx- 
imate equivalent of the Bertie waterlime or the Akron dolomite. The 
beds with the Spirifer crispus fauna appear to represent the youngest 
member of the dolomitic formation called by Cameron 1 the Fitzgerald 
dolomite (Plate II, figure 1). At various points on the north bank of the 
river the gypsum beds and associated buff-coloured, slightly magnesian 
limestones which furnish the fossils listed above are overlaid by a set of 
sharply contrasted sediments holding an entirely different fauna and lying 
unconformably upon the lower beds. The following section shows the two 
formations exposed in a single cliff section. 
Section $ Miles Below Upper End of Cliffs 
Feet 
(a) Lake clay 6 
(b) Glacial clay and boulders 9 
(c) Blue shale and thin-bedded limestone with Devonian fossils abundant 8 
(d) Gx*ey, thin-bedded, hard, argillaceous limestone with a metallic ring, lower third 
brecciated 70 
Devonian Beds 
The foregoing section was taken at a point where the cliffs have 
about their maximum height and where the gypsum shales are represented 
chiefly by limestones. These lower beds, d, of the limestone section, show 
1 Cameron, A. E.: 
1917, pt. C. 
“Explorations in the Vicinity of Great Slave Lake”; 
Geol. Surv., Canada, Sum, Kept. 
