116 FRANK D. ADAMS 
ranges. The thrusts which closed up these mediterranea and developed 
mountain ranges from them, were exerted in a northeasterly direction 
against the southwestern part of the continent, and in a northwesterly 
direction against the southeastern border of the continent, so 
that the folds are parallel to the margin. of the present continent 
of Laurentia. If we inquire whether similar long, narrow, belt- 
like mediterranea existed in Laurentia in pre-Cambrian times, 
the answer seems to be in the negative. The surface of the con- 
tinent seems rather to have had upon it at intervals throughout 
geological time a succession of large, irregular-shaped bodies of water, 
somewhat resembling the present Hudson’s Bay, in which, however, 
great thicknesses of sediment were accumulated. 
The sediments deposited in these bodies of water in Keewatin, 
Grenville, and the Earlier Huronian times, were folded up into moun- 
tain ranges crossing the southern portion of the protaxis in a north- 
easterly and southwesterly direction, coinciding with the course of 
the Appalachian folding. 
The intense diastrophism which brought to a close the Eo-Protero- 
zoic and again the Meso-Proterozoic time was exerted apparently 
as far north as the middle of Labrador and the southern portion of 
Hudson’s Bay. 
In the later pre-Cambrian mediterranea the Nastapoka-Animikie 
series and the Athabasca-Keweenawan series were deposited. The 
almost entire absence of orogenic movement at the close of this time, 
combined with the great extent and comparatively unaltered character 
of the rocks, makes the break at the base of the Nastapoka-Animikie 
series probably the most pronounced in the whole pre-Cambrian 
succession in Laurentia. Thousands of square miles of practically 
flat-lying sediments overlie remnants of a highly folded and meta- 
morphosed antecedent series. : 
We thus have two major breaks in the pre-Cambrian succession, 
each marked by an epoch of diastrophism which exhausted itself for 
the time. 
An identical series of two major breaks in the Proterozoic suc- 
cession, marked by epochs of pronounced diastrophism which in 
each case exhausted itself, is found in the Asiatic portion of the 
nucleus. 
