Islands of Group IV.
The discovery of the Silurian limestone of the southern cliffs of North Devon and Cornwallis was made by Parry, while his collection of fossils was supplemented by those found by the Franklin search expeditions. Our knowledge of the geology of Ellesmere was, previous to the Sverdrup expedition, mainly due to the work of Feilden and De Rance in connection with the British expedition of 1875-76. Mr. P. Schei, the geologist who accompanied Sverdrup, collected much valuable information concerning the rock formations of Ellesmere. A summary of his observations is published as an appendix to Sverdrup’s ‘New Land,’ and is freely quoted from in the following.
The rocks found on the north side of the Archer plateau, in the eastern part of Ellesmere to the north of Cape Sabine, are very interesting geologically, as they show the only trace of an unbroken sequence of beds from the Huronian up through the Cambrian to the Silurian limestones so widely distributed on the Arctic islands. These rocks are described by Schei as follows:
‘At Cape Camperdown, on Bache peninsula, is found granite overlain by an arkose-like conglomerate sandstone, in flat strata, the dip being north-northwest. Its thickness here probably does not exceed 500 feet, though the contour swells to considerably greater magnitude by reason of intrusions of diabase, occasioning an additional thickness of perhaps 300 feet. At its upper part this sandstone merges gradually, by interstratification, into a series of gray, sandy and marl-like schists and limestone conglomerates. From a few inches up to a couple of yards in thickness these conglomerates and schists, continuously interstratified, build up a series 600 to 900 feet in thickness, interrupted by two compact beds of yellowish-gray dolomitic limestone about 150 feet in thickness. These are again overlain by a series similar to the underlying one, excepting that here the limestone conglomerates exceed the schists.’
‘In a detached block, in all probability originating from one of the two 150-foot beds, were traces of fossils, of which one, Leptoplastus sp., can be identified. In another detached block, whose mother rock is not known, was found Anomocare sp. It may be said with certainty after the finding of these fossils that this series contains deposits of the Cambrian age.’
‘The second series of conglomerates is overlain by a light grayish-white limestone in a bed some 300 feet in thickness, observed in the midst of the section of Cape Victoria Head. Indistinct Orthoceras, Lichas and Symphysurus assign this limestone to the Lower Silurian period.’
‘Above the othoceras-bearing, light-coloured limestone bed are some less extensive strata of alternating limestone and quartz-sandstone, and finally a 100-foot bed of close brown limestone of which certain layers are fossiliferous, and gave an Asaphus, traces of other Trilobites and some Gasteropods.’
‘Following the direction of the dip to the north side of Princess Marie bay we find it again, though seemingly somewhat abrupter, in the limestone beds of Norman Lockyer island. A fauna with Halysites sp., Zaphrentis sp., Orthisina sp., Rhynchonella sp., Leperditia sp., Illœnus sp., &c., assigns this limestone to Lower Silurian. It is again found with its fauna at the base of Cape Harrison; in this case with a thick super-incumbent bed of marly sandstone, quartz-sandstone, and finally extensive limestone conglomerate. This also occurs near the shore in Cape Prescott, indicating by its presence in the strike of the limestone of Norman Lockyer island the disturbance undergone by these tracts.
‘The line along which this disturbance took place is refound on the west side of Franklin Pierce bay, where the beds of limestone conglomerate dipping from the heights of Cape Harrison are cut off in the strike by a limestone, dark-gray in colour and broken into a breccia.’
In another place Schei hints that the rocks of the Cape Rawson beds, consisting largely of dark shales and impure limestones, found along the northern parts of the eastern shores of Ellesmere, may be of Triassic age, in sharply folded troughs of the older rocks, and consequently much younger than Cambrian, to which age they were referred by Fielden and De Rance.
Writing of the Silurian beds found on the southern coast of Ellesmere, Schei describes them as answering to the northern series, and their occurrence is as follows:—
‘There are at Havnefjord, in Jones sound, above some layers of quartz-sandstone, which entirely cover the gneiss-granite there, a series of limestone conglomerates with marly schists and pure limestones of a thickness of 1,200 to 1,500 feet. These are again overlain by a series of beds at least 2,000 feet thick, of hard, impure limestones, brown or yellowish-gray in colour, and often remarkably heavy.’
‘At South cape, which is entirely composed of this brown limestone, are found in the lower parts Maclurea sp., and Halysites sp., referable to the Middle Silurian, while west of it, at Bjorneborg, the upper parts of the series contain badly preserved remains of Orthocerata, Corals, and Pentamerus cfr. tenuistriatus. Hereafter the upper part of the limestone seems to be equivalent to the older Upper Silurian (Landovery). This brown limestone occurs from South cape westward to Kobbebugten in Hell Gate, and is broken at Lille Sandor, tectonic disturbance bringing up the underlying conglomerate series, and even the Archæan.’
‘On the south side of Rendalen appears the brown limestone of the capes, Series A, with a flat dip to the north-northwest; but on the north side of the valley is a division of dark schist, Series B, lying conformably above the beds of brown limestone. Associated with these schists, particularly in their lower and upper parts, are numerous layers of pure dark limestone, frequently fossiliferous. In Rendalen and in Kobbebugten, where this same division also appears, a quantity of material was collected, of which fifteen species are provisionally determined, among them being Favosites sp., Strophomena cfr. euglypha, Meristella in numbers, Rhynchonella cfr. borealis, Pentamerus cfr. galeatus, Spirifer cfr. elevatus. The period of this division in Series B is Wenlock.’
‘The upper part of Series B appears, among other places, at the headland north of Tunneldalen, in Hvalrosfjord. Above a black shale containing Monograptus sp. and Leperditia cfr. phaseolus is a bed of fragmentary limestone with Favosites, Strophomena cfr. pecten, Atrypa reticularis, Pterniea cfr. Sowerbyi. From a locality in Gaasefjord, on the same horizon, were taken Favosites cfr. Hisingeri, Favosites Gothlandicus, Thecia Swinderenana, Spirifer elevatus, Spirifer cfr. crispus, Strophomena corrugatella, Dav., Pterinea sp. According to these, the period of this upper part of Series B should be Ludlow. The thickness of the series is about 1,000 feet.’
‘In Hell Gate, as well as in Gaasefjord, these strata are overlaid by Series C; in its lower parts consisting of interstratified light and dark marl schists, which are somewhat sandy, while in its upper part appear pure quartz-sandstone beds and argillaceous sandstone. The collective thickness of these strata is about 1,000 feet in Gaasefjord, while in Hell Gate it is probably somewhat greater. No fossils were found in this series.’
‘At the base of the high cliffs at Indra Eide and Borgen appears Series C. In both of these places it is overlain by a dark limestone and black shale, partially fossiliferous. This dark limestone and shale are the lowest layers in a series of strata at least 1,500 feet in thickness, Series D, which appears in the profiles on both sides of Gaasefjord, from Borgen to the foot of Vargtoppen (Wolf Top), and from Indre Eide to Skrabdalen.’
‘In Series Da occurs Atrypa reticularis in great quantities, but little else. On the other hand, there are preliminary determined in Db about fifty-five species, of which may be mentioned: Favosites sp. div., Columnaria sp., Cyathophyllum sp. cfr. hexagonum, Recaplaculites sp., Fenestella sp., Homalonotus sp., Burmeisteria sp., Dechenella sp., Proetus sp., Orthis striatula, Leptaena sp., Strophomena, Streptorhyncus, Atrypa reticularis, aspera; Rhynchonella (Pugnax) cfr. reniformis, pugnus, Productus cfr. prolongus, Spirifer of the Verneuilli Murch. type, a peculiar Pentameride, Terebratula cfr. Dielasma, Pterinea sp., Modiolopsis sp., Lucina sp. div., Bellerophon sp., Platyceras sp., Orthoceras sp., Gomphoceras, gigantic nautilus and ganoid scales.’
‘The fauna in Dc is merely a repetition, and in the case of certain species, a further development, of the forms found in Db. It will thus be seen that there is a spring in regard to the fauna between the upper layers in Series B and the lower ones in Series D, which more particularly resemble Lower or Middle Devonian. The concordantly embedded (?) Series C might, therefore, be thought to represent uppermost Silurian as well as lowest Devonian.’
‘Divisions Dd and Df are poor in fossils, and are partly shale divisions. In the impure limestone of Dg occur again numerous fossils, among which are Atrypa reticularis, Rhynchonella cfr. cuboides, Spirifer cfr. undifera, Productus sp., Terebratula cfr. Dielasma, Pterinea sp., Avicula sp., Modiolopsis sp., Pleurotomaria sp., Proetus sp. Traces of placoderm fish are also met with. Above these strata are beds of purer limestone Dh, and above these again some less pure, Di. The uppermost strata of Di alternate with strata of light-gray quartz-sandstone terminating in a clay-sandstone, which in places is richly fossiliferous, though the fossils are in a bad state of preservation. Among these are lamellibranchiata, Dechenella sp., remains of Holoptychius, &c.’
‘This argillaceous sandstone is simultaneously the last link in Series D and the first in Series E. This is a huge collection of quartz-sandstone strata building up the mountains on both sides of the inner part of Gaasefjord. The lowest part, which is 900 to 1,200 feet in thickness, consists almost exclusively of quartz-sandstone. On the north side of Skrabdalen, in the sandstone profile, occur conglomerate strata, half an inch to an inch in thickness. In these were found considerable remains of Coccosteus sp., Holoptychius sp., and Modolia angusta. In the same strata with these were also seen indeterminable plant-fossils. Slightly higher up in the profile, however, in a black shale which occurred in two lentiform masses, eighteen inches and six feet in thickness, were found numerous plant-fossils.’
‘Professor Nathorst, of Stockholm, who has kindly undertaken the examination of these, says that among others are Archœopteris fissilis Schmalh. and Arch. archetypus Schmalh., both characteristic of Upper Devonian. In examining the material collected, Professor Nathorst also found with the plant remains some remains of fishes.’
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.