BASIS OF PRE-CAMBRIAN CORRELATION Taig 
nian at Port Arthur, and largely on these grounds the Animikie or 
Upper Huronian of the Lake Superior region and the Nastapoka 
series of Labrador and the territories south and west of Hudson Bay 
been have considered to be equivalent to one another. 
The Nastapoka-Animikie series, forming the third major division 
of the pre-Cambrian in Laurentia, is of great importance, marking 
as it does one of the most widespread periods of submergence and 
depression in pre-Cambrian times, involving almost the whole con- 
tinent of Laurentia. No division of the pre-Cambrian in Laurentia 
is exposed over such a great area of country. The positive move- 
ment which raised these rocks out of the sea was chiefly epeirogenic in 
character, for over the greater part of this area they still lie nearly flat. 
That the close of this time was, like those which preceded it, marked 
by an epoch of diastrophism, is shown by the widespread develop- 
ment of faults, accompanied in places by overthrusting. These are 
_ the superficial expression of the movements of deepseated intrusions, 
representing the last period of pre-Cambrian orogenic action. These 
post-Animikie granitic intrusions are to be seen on the east coast of 
Hudson Bay where, while the Nastapoka series in most places lies 
unconformably on the ancient Laurentian and the associated gneisses 
and schists, yet at some points it is cut by granitic intrusions. 
This epoch of mild diastrophism brought to a close the third great 
period in the pre-Cambrian history of Laurentia. 
The Nastapoka series seems to be the youngest division of the 
pre-Cambrian now found in the region east of Hudson Bay, but west 
_ of this inland sea, in a district bordering the southern shores of Lake 
Athabasca and stretching over an area of perhaps 24,000 square miles, 
is a great development of coarse sandstone in thick beds which along 
the shores of the lake aggregate at least four hundred feet in thickness. 
These, the Athabasca sandstones, lie in nearly horizontal positions, 
at times with a conglomerate layer at their base composed of fragments 
of the Laurentian granites and gneisses on which they rest with a 
strong unconformity. ‘The Athabasca sandstones, or a very similar 
series, are exposed for a long distance up the valley which is continued 
seaward by Chesterfield Inlet, situated far north on the western shores 
of Hudson Bay. Between Lake Athabasca and the above locality, 
and in places associated with similar sandstones, are extensive areas 
