38 THE MAEQUETTE lEON-BEAKING DISTRICT. 



Cambriau age, the discordance between tlieni Ijeing- explained as due to 

 dislocations caused by the granite. Even the sandstone near Marquette 

 is supposed to have suffered fracturing, etc., tlirough the action of the 

 gi'anite. The unconformity at Granite Point is not referred to specifically. 

 Later observations have shown that nearly all of Rivot's generaliza- 

 tions regai'ding the origin of the metaraorphic rocks and their relations 

 to one another are erroneous. 



1S57. 



Whitney, J. D. Remarks ou the Huroniau and Laureutian systems of the 

 Canada Geological Survey. Am. Jour. Sci. (2), Vol. XXIII, 1857, pages .305-314. 



Whitney, in 1857, published an article which, while it does not treat 

 directly of the Marquette rocks, does so indirectly. The Canadian geolo- 

 gists, as a result of their studies, had come to the conclusion that under 

 the Potsdam of the western Great Lakes there are two great unconform- 

 able series of rocks, called by them the Laurentian and the Hurouian series. 

 The piu'pose of Whitney's article is the denial of the existence of two 

 series beneath the Potsdam of the south shore of Lake Supeiior. 



1859. 



Leslie, J. P. The iron manufacturer's guide to the furnaces, forges, and 

 rolling mills of the United States, etc. Isevf York, 1859. Tages 480-489. 



This author gives a very generalized account of the ores of Marquette, 

 the descriptions of their geology being taken mainly from the reports of 

 Foster and Whitney and of Rivot. The ores are said to be in a gaugue 

 rock, consisting of a mixture of quartz and a silicate of iron, alumina, and 

 lime. 



Whittlesey, Charles. On the origin of the Azoic rocks of Michigan and 

 Wisconsin. Proc Am. Ass. Adv. Sci., Vol. XIII, 1859, i)ages 301-308. 



Charles AVhittlesey, in this article, deals with the Marquette district only 

 as a portion of a larger Azoic area. From the results of cliemical analyses of 

 many rock specimens collected from northern Wisconsin and Upper Michi- 

 gan he concludes that there are two metamorphic series in the Azoic, both 

 older than the Potsdam, one characterized by the presence of the alkalis. 



