From the above it will be seen that on the southern side of Ellesmere there is a complete succession of strata, bearing fossils from Middle Silurian age up to the Upper Devonian. These strata have an aggregate thickness of 8,000 feet, and form the thickest and most carefully measured section of the Silurian and Devonian beds of the Arctics.
On the southern and southwestern parts of North Devon the Silurian strata are much thinner than those described by Schei. At Cuming creek the Archæan gneisses were found overlain unconformably by red and purple arenaceous shales and thin bedded sandstones having an aggregate thickness of fifty to one hundred feet. These in turn were succeeded by beds of impure limestone of light-gray or creamy colour. The beds are usually under two feet in thickness, and separated by thinner beds containing a considerable amount of clay. These light-coloured limestones have a thickness of over 1,000 feet in the cliffs on both sides of the creek. The sides of the cliffs are covered with broken limestone, so that it was impossible to measure a section up them, but in two or three places a darker coloured limestone conglomerate was found, made up of small pebbles cemented by a dark shaly matrix. Fossils are only found in the beds immediately overlying the dark shales and sandstones of the base. These show that the lower limestone is of Silurian age, about the horizon of the Niagara.
Limestone Cliffs of North Devon Island.
Similar conditions prevail in the cliffs at Beechey island, where a large collection of fossils was obtained from the lower limestone beds, while others, picked up loose, but evidently fallen from the cliffs above showed that the upper beds passed close to if not into the Devonian, as stated in Appendix IV.
Similar Silurian limestones constitute the island of Cornwallis, to the westward of North Devon, while in the remaining Parry islands farther west the Silurian strata are lost beneath the Devonian and Carboniferous rocks of those islands.
DEVONIAN.
The work of the older geologists, which was summarized by Haughton and later by Dawson, took no account of the Devonian in their divisions of the Palæozoic rocks of the islands north of Lancaster sound. All the lower limestones were classed as Silurian, while the overlying sandstones were placed in the Carboniferous. Fossils of Devonian age were collected, by the expedition of 1876, from the northern part of Ellesmere, but their occurrence and relations were only finally settled by Schei as given above. From his observations it is plain that the upper part of the limestones and the lower 1,000 feet of the overlying sandstones are of Devonian age. The early explorers were not trained geologists, and it could hardly be expected that they would discover the thin bands containing fossils in these great thicknesses of barren beds. Owing to this supposed lack of fossils the rocks were separated into Silurian and Carboniferous almost wholly on lithological differences, the limestones being classed as Silurian and the sandstones as Carboniferous.
There is no doubt that Devonian rocks are included in the Carboniferous of the western Parry islands, but as they occur only in the cliffs underlying the Carboniferous beds that cover the surface of the islands, it would be impossible to map them on the scale used in illustrating this report, and in consequence the old colouring is followed here.