Only isolated attempts have been made to subdivide the Archæan complex into Laurentian, Huronian and other members of the system. This lack of subdivision is due to want of detailed knowledge; not to the absence of the various members of the complex in these northern regions, where the greater number of the members are known to occur.
The Palæozoic rocks are well represented on the islands by thick deposits extending upwards in a continuous series from the Cambro-Silurian to the upper beds of the Carboniferous. Rocks older than the Galena-Trenton are only found in the northern part of Ellesmere island, where a series of beds appears to connect the Upper Huronian formations with the lower members of the Cambro-Silurian.
Mesozoic rocks are found on the northern Parry islands, on the Sverdrup group and on the western and northern sides of Ellesmere island.
Tertiary formations occur on the northwestern islands, on the northern part of Ellesmere, as well as on the northern and eastern parts of Baffin island.
The former presence of a continental ice-cap is attested along the northwestern shores of Hudson bay and in the southern part of Baffin island, by the rounded and polished rock surfaces, which are everywhere well marked by the ice striae, often in several sets showing changes in the direction of the ice movement. On the east side of Baffin the rock surfaces show signs of rounding and smoothing by ice, but the striae are not well marked, and the glaciation does not appear to have been nearly so intense as to the south and westward. Passing northward up the western side of Davis strait and Baffin bay the evidence of intense glaciation becomes less and less, that on Ellesmere the present condition of the local ice-covering would appear to represent nearly as great an amount of glaciation as ever occurred there.
The sequence of earth movements and physical conditions, read from the geological formations of the northeast, are as follows: An ancient floor of crystalline rocks, largely of igneous origin, represents the most ancient crust of the earth. These, associated with ancient bedded deposits and cut by dark basic intrusions of trap and allied rocks, were at a very early period so crushed and foliated that it is now impossible to separate them. Upon this ancient complex was laid down a series of bedded deposits, chiefly sandstones and dolomites, associated with contemporaneous traps, as may be seen along both the shores of Smith sound. Following this came a great outburst of granite and other acidic igneous rocks which, over large areas, inclosed, penetrated, compressed and otherwise altered the sedimentary deposits to such an extent that it is now impossible to separate them from the older complex upon which they were originally deposited. Only in a few comparatively small areas were the conditions of the granite intrusion such as to allow the sedimentary deposits to preserve their original unaltered conditions. All the above rocks are grouped in the Archæan, and further and closer examination will probably show that it contains all the members of the Laurentian and Huronian found in the more southern Archæan regions of Canada.
Except in the northern part of Ellesmere, there is a considerable time-break in the geological sequence in the northeast between the Archæan rocks and the Cambro-Silurian strata which rest unconformably upon them. Schei found at Bache peninsula, on the eastern side of Ellesmere, a series of stratified sedimentary rocks resting upon the northern flank of the Archæan and containing fossils of Cambrian age. These deposits have a thickness of nearly 1,500 feet, and are overlaid by limestones containing Cambro-Silurian fossils.
The Archæan rocks at the time of deposition of the lower beds of the Cambro-Silurian limestones appear to have extended southward from the vicinity of Bache peninsula in a gradually widening ridge along the western side of Baffin bay and Davis strait. In this manner they attained a width of seventy miles on the southern side of North Devon, and occupied the entire southern shore of Baffin island, being separated from the great area of Labrador by the depression of Hudson strait, which probably existed at that early period. Islands of Archæan rocks may also have risen above the surface of the Cambro-Silurian sea in the present island of North Somerset and on Melville and Boothia peninsulas, as well as on other portions of the northern coasts of the mainland, to the west of Hudson bay.
The western Cambro-Silurian sea filled the present depression of Hudson bay, and extended far to the south and westward of its present limits, outliers of limestone containing fossils of this age, and very similar in mineral character, being found in the valleys of the great lakes of Manitoba. From Manitoba these rocks have been traced southward into the United States, so that at the time of their deposition the Cambro-Silurian sea occupied a great basin open to the Arctic ocean and extending southward into the middle of the continent.
This was the time of maximum encroachment of the northern ocean, after which the land gradually rose, and the sea slowly receded. Owing to the great lapse of time and the eroding of the thick ice-cap in the more southern regions, it is exceedingly difficult to now trace the boundaries of the narrowing sea during Silurian and Devonian times. Cambro-Silurian limestones containing fossils which refer them to the Galena-Trenton, are widespread over the northern islands and in a wide margin along the western and southern shores of Hudson bay. Outliers of these rocks occur at the head of Frobisher bay in the southwest part of Baffin island and on Akpatok island in Ungava bay. As before stated, similar limestones are found in the lake valleys of Manitoba, and it is quite possible that these limestones were once continuous with those of Hudson bay, the present break having been caused by the erosion of the glacier.