466 



GEOLOGY OF CENTRAL WISCONSIN. 



building stones, especially ornamental building granite. Beds large- 

 ly charged with the specular and magnetic oxides of iron occur on 

 Black river, but, so far as known, contain too little iron to be jised as 

 ores of that metal. Judging from the character of the rocks of this 

 age in Canada, a great variety of materials of economic importance 

 might reasonably be expected, including the precious metals, lead, 

 copper and iron ores, all of which are found and profitably worked in 

 the Canadian Archtean. Small traces of precious metals have been 

 found in quartz from Clark county. Details as to the kaolins of the 

 Black, Yellow and "Wisconsin rivers, and as to the ornamental granites 

 of Yellow river and other places, are given on subsequent pages. 

 Both of these materials are obtainable in large qtiantity, and are des- 

 tined to become important factors in the industries of the state. The 

 red granites are quite extraordinary in their fine qualities, and are 

 hardly to be equaled by any in the country. 



Fig. 2. 



II. Local Details. 



The various rock exposures belonging to the main Archaean area 

 which have been examined by the writer, are chiefly in the vicinities 

 of the three main streams, the "Wisconsin, Yellow and Black, and 

 their tributaries. A corresponding grouping of the detailed descrip- 

 tions is here adopted, the valley of each stream being followed up 

 wards from its southernmost crystalline-rock exposure. 



Upper Wisoonsin Yalley. 



At Whitney's Rapids, near Point Bass, on the S. W. qr. of Sec. 10, a,nd the N. W. 

 qr. of Sec. 15, T. 21, R. 5 E., occur the southernmost exposures 

 of crystalline rooks on the Wisconsin river. They are here con- 

 fined entii-ely to the river bed, the liorizontal Potsdam sandstone 

 overlying tliem in the banks. The following sketch map serves 

 to show the occurrence of the various outcrops at this point. 



The southernmost exposm-e seen, and this only at unusually low 

 stages of the water, is a low rounded one of quartzose gneiss (869), 

 a few square yai-ds in area, in the river bed at the point E of the 

 map. Ten paces up the stream from here is a similar exposure 

 of a greenish-black, pyritiferous, homblendic rock (870), traversed 

 l)y pinlrish felspathio vems, and striking N. 50° E., 'with a nearly 

 vertical dip. Continuing northward along tlie bed of the stream, 

 between the western shore and the island I), we find occasional 

 exposures of decomposing gneiss, which is, for the most part, 

 1 %% concealed by water and river gravel. At about eighty paces, a 



I S ! ^m I ^^'^*^°" ^™°^^ ^'■^e stream was taken, on the line C D of the map 



V,c:nx.vo.Po™t Bass, "^''^l " ^P-^esented by Fig 3. Here the white, kaolh^ized, but 

 Wood County. '*'^^ *"^' ^"'"'° ^^ks (871) are overiaid by 2 to 6 inches o!' 

 sandstone, the lowest layer of which, about 2 inches thick, in 

 highly charged with pyrite, wliich, in places, excludes the sand 

 'All bearings are reforrea to the true merlrliiin. 



Wood County. 

 Scale, 1 mile to the inch. 



