460 THE CRYSTAL FALLS IRON-BEARING DISTRICT. 



and argillaceous slates in Ts. 42 and 43, Rs. 29, 30, etc., of mica-slates in 

 Ts. 41 and 42, Rs. 29, 30, etc., and of "calciferous sandrock" near the south 

 boundar}^ of T. 42 N., Rs. 27 and 28 W. 



In a list of specimens gathered from these townships Burt^ mentions 

 sienitic greenstone, trap, granite, granulite, and talco-micaceous slate. On 

 the land plats made by these surveyors conglomerate is noted on the west 

 line of sec. 8, T. 42 N., R. 28 W., and marble at the south corner between 

 sections 3 and 4 in the same township. 



In 1851 Messrs. Foster and Whitney reported^ the existence of an arm 

 of Azoic rocks about 18 miles in length and 10 in breadth, extending east- 

 erly into Ts. 42 and 43 N., R. 28 W., and located its position on their map 

 of the Upper Peninsula. 



Brooks,^ in his description of the northern iron belt of the Menominee 

 district, refers to the existence of outcrops of hornblendic rocks, mica- 

 schists, and gneisses, cut by trap dikes, which he regarded as equivalents 

 of the various greenstone-schists exposed along the Menominee River. 

 "Near the center of this hornblendic belt, in the north part of sees. 22, 23, 

 and 24, T. 42 N., R. 29 W., a line of weak magnetic atti-action was observed. 

 Tliis is regarded as an indication here of the existence of an iron-ore belt." 



The gneiss, granite, etc., north of the, north quarter post of sec. 31, 

 T. 42 N., R. 29 W., he declares to have the appearance of typical Laurentian 

 rocks. "If future investigations prove them to be Laurentian, a very 

 troublesome structural problem woiild be presented here, as we would have 

 Laurentian rocks conformably overlying beds unmistakably Huronian."* 



The only distinct reference made by Brooks to the sedimentary beds 

 of the district is in the following paragraph:^ 



A range of marble associated with quartzite, chloritic and talcose rock, and 

 overlaid by a chloritic gneiss, with beds of chloritic schist and gneissoid conglom- 

 erate, the whole dipping at a high angle to the south, passes about 5 miles north of 



> Geological report of tlie survey of a district of township lines in the State of Michigan, in the 

 year 1846, by Wm. A. Burt: Thirty-first Congress, first session, 1849-50, Senate Documents, Vol. Ill, 

 No. l,p.84. 



' Report on the geology and topography of the Lake Superior land district, by J. W. Foster 

 and J. D. Whitney, Part II, The Iron Region: Thirty-second Congress, special session, 1851, Senate 

 Documents Vol. Ill, No. 4, p. 14. 



'Iron-Bearing Rocks (economic), hy T. B. Brooks: Geol. Survey of Michigan, Vol.1, 1869-1873, 

 N. Y., 1873, p. 161. 



< Op. cit., p. 175. ^ Op. cit., p. 176. 



