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 used 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 Archaean. 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 quantity, 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. 



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 WISCONSIN VALLEY. 



FIG. 2. 



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

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

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

 fined entirely to the river bed, the horizontal Potsdam sandstone 

 overlying them in the banks. The following sketch map serves 

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



The southernmost exposure seen, and this only at unusually low 

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

 a few square yards 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, hornblendic rock (870), traversed 

 by pinkish felspathic veins, and striking N. 50 E.^with a nearly 

 vertical dip. Continuing northward along the 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, 

 v jmm concealed by water and river gravel. At about eighty paces, a 



i i wfm sec ti n across the stream was taken, on the line C D of the map, 



' ' which is represented by Fig. 3. Here the white, kaolinized, bill, 



VICINITY OF POINT BASS, ,>, i /OI-M\ 1-11 /* 



still firm, gneissic rocks (871) are overlaid by 2 to 6 inches of 

 V> OOD COUNTY. 



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

 Scale, 1 mile to the inch. , . , , , , ... .. .... . 



highly charged with pyrite, which, ui places, excludes the sand 

 1 All bearings are referred to the true meridinn. 



