The upward continuation of these limestones containing Silurian fossils occupies a corresponding but slightly circumscribed area. These Silurian limestones form the characteristic abrupt cliffs of the islands on both sides of Lancaster sound, and continuing southward occupy the larger parts of Southampton, Coats and Mansfield islands in Hudson bay, as well as the low lands of the western part of Baffin island. They are not well marked, and are probably considerably thinner on the western side of Hudson bay, but are found in the Winnipeg basin.
The Devonian gradually emerges from the Silurian in the cliffs of the islands to the north of Lancaster sound, and forms the lower parts of the cliffs of the southern side of Ellesmere. Devonian fossils are not found in the limestones of the islands of Hudson bay, and only occur in a narrow belt on the low lands to the west and southwest of James bay. Similar rocks form the upper beds of the Winnipeg basin.
There is no break in the passage from Devonian to Carboniferous in the rocks forming the Parry islands and the southern part of Ellesmere, where Carboniferous rocks occupy wide areas on these northern islands, but are not found to the southward of Lancaster sound, showing that the Palæozoic sea had retreated that far north before the close of the Devonian.
The land rose above the ocean at the close of the Carboniferous, and with the exception of the northern parts of the Parry islands, the Sverdrup group and the western part of Ellesmere has not been deeply submerged since. Rocks of Mesozoic age, belonging to the Alpine Triassic, have been found in the last-named places, but in no other localities to the southward within the limits of this report.
Considerable earth movements occurred at the close of the Mesozoic period, causing those and older rocks to be highly tilted and folded.
Another slight submergence took place in the Miocene Tertiary, when shallow water deposits of sand, gravel and clay, associated with beds of lignite, were laid down in the wide valleys along the margins of several of the Arctic islands. Such deposits are known to exist in Banks island, on the western side of Ellesmere and along the northern and eastern sides of Baffin island. There is little doubt that other deposits of this age will be discovered when more systematic search has been made for them in these northern regions. From the character of the fossil plants found in these deposits there can be little doubt that during the Miocene the climate of these northern islands was much warmer than at present, and approached a tropical condition.
The conditions of the land and water surfaces during the Glacial period differed little from those at present, except that there has been a considerable uplift of the land, as proved by the marine terraces found along the coasts. The maximum uplift probably amounted to 700 feet along the eastern side of Baffin island, and was perhaps slightly less on the islands farther north, where Schei reports beaches 600 feet and upwards above the present sea level. This being the case, a new explanation must be found for the depression and subsequent uplift of the land covered by ice, if the uplift be practically the same in northern Ellesmere, where the accumulation of ice is nearly as great to-day as at any previous time, while in the southern part of Baffin island a great thickness of ice was present during the Glacial period and has now completely disappeared. Perhaps we have been taking cause for effect, and the uplift due to some unknown cause may have been the cause of a lessening of the ice; certainly the almost equal rise of the land throughout the Arctic islands is an argument against the subsidence of the northern lands being due to the burden of the ice-cap, and the subsequent uplift due to the disappearance of that burden.
DETAILS OF THE GEOLOGY BY ISLAND GROUPS.
It is exceedingly difficult to write a readable, concise and comprehensive account of the geology of the territory included in this report without subdividing it in some manner. This has been attempted by considering the different formations under their separate headings, and dividing the territory, as has been done in the geographical description, into groups of islands, and considering each of the great geological divisions separately.