l6 FRANK D. ADAMS 



while on the Atlantic shores, far north, is found a great group present- 

 ing many like features. West of James Bay and south of Hudson 

 Bay, rocks lithologically like the Nastapoka series underlie a liilly 

 district rising like an island above the surrounding flat -lying Paleozoic 

 beds. In this great district of the pre-Cambrian west of Hudson 

 Bay, large areas bordering the Arctic about the mouth of the Copper- 

 mine River, and extending to Great Bear Lake, are underlain by a 

 development of rocks resembling in nearly all respects the Nastapoka 

 series and similar rocks have been described from the region about 

 Great Slave Lake. 



In all these widely separated localities great developments of 

 the same rocks occur and often are accompanied by beds of jaspilite 

 and iron ore. Everywhere the members present the same general 

 arrangement, the strata cut by many faults, dipping at comparatively 

 low angles and forming ridges frequently capped by diabase, while 

 in most cases the beds have been found overlying with a most striking 

 unconformity older granitic and gneissic rocks. These points of 

 similarity seem to indicate that the scattered groups are all of about 

 the same age and belong to a pre-Cambrian series probably at one 

 time nearly continuous over the northern regions from the shores 

 of the north Atlantic to about the valley of the Mackenzie. In Labra- 

 dor and in the districts west of Hudson Bay the evidence indicates 

 that the Nastapoka series was deposited after an epoch of severe 

 erosion. Lake Mistassini, in northern Quebec, lies in a basin-like 

 depression occupied by nearly flat-lying beds of cherty dolomite 

 representing a portion of the Nastapoka series, while south of the 

 lake these rocks have been found almost in contact with a develop- 

 ment of the Lower (or Middle) Huronian, differing in no essential 

 features from this group of rocks as found in numerous localities 

 further southwest toward Lake Superior. The Lower Huronian is 

 in a highly disturbed condition and has been penetrated by large 

 bodies of granite. Neither the disturbances nor the granitic intrusions 

 have affected the near-lying Nastapoka series so that the latter seems 

 to be undoubtedly of post-Lower (or Middle) Huronian age, to have 

 been formed after the Lower Huronian had been folded and invaded 

 by the granites and then deeply eroded. The relation of the two 

 series resembles that existing between the Animikie and Lower Huro- 



