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CANADA. 



337 



rocks of Lake Huron, and therefore those of Lake Snperior, were re- 

 garded as being of Cambrian age. 



In the lleport of Progress for 184:8-4:9, Mr. Murray again reported 

 on the region north of Lake Huron. He arranges the rocks along the 

 Spani^li Itiver into two series : the granitic or metamorpliic group, and 

 the quartz roch group. The first group "appeared to rise from beneath 

 the rocks of the second group in two different locahties," but no evidence 

 seems to have been found to show the relations of the two supposed 

 formations except the finding of pebbles of granite or sj^enite in some of 

 the conglomerates of the second group. The rocks of the first group 

 were said to be granite or syenite, except the following : — ■ 



" A gneisaoitl structure was observed on one or two occasions, but it was for 

 the most part obscure and ill-defined, being perceptible rather in a longitudinal 

 arrangerneut of the constituent minerals, than in conspicuous beds of different 

 r[uulity." (/. c, pp. 3C-42.) 



In the Report of Progress for 1849-50, a ti'act of country on the St. 

 Lawrence lUver, between Bay St. Paul and Murray Bay, was described. 

 Hero the metaraorphic group, consisting of gneiss, was overlain by 

 white quartz rock (Potsdam sandstone). {I. c, pp. 8-10.) In the Re- 

 port for 1851-52, the inetamorjMc or gneissoid group is likewise said 

 to be overlain by Potsdam sandstone in the country between Bcauhar- 

 nois and the Riviere du Nord. {L c, p. (J.) 



In tlie Quarterly Journal of the Geological Society (Vol. VIIL, 1852, 

 p. 210), Mr. Logan states regarding the rocks north of Lake Huron : 



" Ou Lake IJuron the Lower Silurian group rests unconTormably upon a 

 siliceous series with only one known band of limestone, of about 150 feet 

 thick, with leaves of chert hi abundance, but as yet without discovered 

 fossils. This scri(!S is supposed to be of the Cambrian epoch. It compre- 

 hends the copper-bearing rocks of that diytrict, and with its igneous inter- 

 stratilied masses has a thickness of at least 10,000 feet. The gneissoid group, 

 of wliich nientiou is made, is probably still older than this. Its conditions 

 appear to me to mnko it reasonable to suppose that it consists of aqueous de- 

 posits in an altered state." 



In the Report for 1852-53, but published in 1854, Mr. Logan 

 writes : — 



" The name which has been given in previous Reports to the rocks underly- 

 ing the fossiliterous formations in this part of Canada is the Metannn-phic 

 Bcries, but inasnnicli as tliis is applicable to any series of rocks in an altered 

 condilion, and miglit occasion confusion, it has been considered expedient to 

 apply to them for the future, the more distinctive appelhition of the Lauren tian 



VOL. VII. — NO. 11. 22 



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