Mil ] LAURKNTIAN 8V8TKM. 15 I) D 



Thk Lai rentian System Around Hudson's Bay. 



The vast Lanrentiun area of the north-eastern part of North America 

 fonnfl a very considerable proportion of the whole continent and, ^eo. 

 logically speaking, it may he regai-dod as its nucleus. Greenland, on NuoieuK of th& 



■ '=' -^ i o^ J f> > continent. 



the other side of Baffins' Bay and Davis' Straits, consists, as far as 

 known, almost altogether of the same rocks. Hudson's Bay, which is 

 nearly half as extensive as the Mediterranean Sea, lies in the middleof 

 the continental portion of the great Laurcnli.u area and the waters 

 drain into it from all sides. The country slopes towards it from the 

 Rocky Mountains, more than 1,300 miles to the westward, from the 

 centre of Labrador, 500 miles to the eastward and from the immediate 

 vicinity of Lake Superior in the south. Thus, the watei-s of this great 

 interior sea occupy only the centre of what may be called the basin of 

 Hudson's Bay. This wide depression has existed from early geological Basin of 

 times, as is shown by the Manitounuck rocks of the eastern shore and 

 islands and by the Silurian limestones of Mansfield and Southampton 

 Lslands and of the southwestern shores of Hudson's Bay and James' 

 Bay, as well as the Devonian rocks of the latter. These flat-lying 

 pahi'ozoic strata probably also extend over much of the bed of the bay, Paiaeoioic 

 judging by its shallowness and the uniform depth of its waters, and also 

 from the composition of the materials of the drift which have been car- 

 ried out of it during the glacial period. None of the unaltered rocks 

 around the Bay have undergone any marked disturbance, so far as 

 known. The observations of Dr. Fj-anz Boas and othei-s around Fox yox Channel. 

 Channel would lead us to suppose that from a geological standpoint 

 this body of water is a repitition of Hudson's Bay on a smaller scale 

 (see above). 



The Manitounuck series is largely made up of rocks of volcanic origin source of 

 and I have obtained specimens of diorites and porphyry from the north- ^^ can>«l'^««» 

 western part of the bay. The probable site of the original source from 

 which these rocks have been derived has not yet been ascertained. A 

 set of immense dykes of trap along the Mattagami River running north 

 waiti towards James' Bay, was described in my report for 1875 ; and 

 other dykes, having the same general course, were found along the east 

 side of James' Bay in 1877. 'N''- irregularity has been found in the bottom 

 of Hudson's Bay which might indicate a seat of volcanic disturbance 

 in former times. The unexplored distx'ict behind Cape Henrietta Maria 

 may yet throw some light on this subject. The volcanic rocks of the 

 Manitounuck group of the Eastmain coast and the islands opposite to it 

 may have been originally derived from the neighbourhood of Clear, ciearwater 

 water Lake to the eastward of Richmond Gulf. Between Lake Superior 



