BASIS OF PRE-CAMBRIAN CORRELATION 15 



sedimentaries were swept away over the greater part of the region, 

 leaving only the lower portion of the folds — the roots of the mountains 

 — in the form of long narrow belts, separated by the granitic 

 rocks marking the axes of ihe intervening antichnal uplifts. This 

 period of profound erosion constitutes what Lawson has termed the 

 Eparchean Interval. Up to this time the movements which affected 

 the continent of Laurentia were due, as has been stated, to thrusts 

 coming from the southeast and caused by the negative element 

 underlying the Paleozoic plain in this direction, at that time con- 

 stituting the ocean bed, by its subsidence crowding against the posi- 

 tive element which formed the continent of Laurentia. This is seen, 

 as has been stated, in the distribution of the older rocks of the first 

 two chapters of the pre-Cambrian in the form of long narrow belts 

 running in a general northeasterly and southwesterly direction and 

 representing the downward sagging portions of the ancient folds. 



Succeeding this long period of intense and widespread erosion, 

 which followed upon the conclusion of Middle Huronian or pre- 

 Animikie time, there was again a very widespread transgression of 

 the sea upon the surface of the continent of Laurentia. In this was 

 laid down a series of sediments Avhich while occurring at localities 

 sometimes separated from one another by hundreds of miles, yet 

 preserve the same general features. These younger rocks form chains 

 of islands fringing the east coast of Hudson Bay over a distance of 

 about three hundred miles and have been described under the title 

 of the Nastapoka series. This assemblage of beds dips toward 

 Hudson Bay, generally at low angles, and lies in long parallel ridges 

 with steep eastern faces. The strata comprise a group of arkoses 

 and sandstones overlain by sandstones, argillites, cherty limestones 

 and dolomites and calcareous shales with great intrusive sheets of 

 diabase. The series has been found in places to have a thickness 

 of at least three thousand feet and is further characterized by the 

 occurrence at certain horizons of beds of banded jaspilite and iron 

 ores. In the interior of Labrador, where the series dips at low angles 

 toward the Atlantic, there is throughout a zone at least three hundred 

 miles long, a development of similar rocks and here again occur the 

 jaspihte beds. On the Atlantic side, at the head of Hamilton inlet, 

 and further up the river of the same name, occurs a similar series, 



