GEOLOGY OF NORTHERK WISCONSIN". 41 



refer to other localities in nortliern Wisconsin and Michigan, in 

 order to present new facts, or to quote those already kiiown, which 

 bear upon points in the geology of the above mentioned district. 



Four great geological formations are represented in northern 

 Wisconsin. 



1. Granitic and gneissic rocks supposed to be the equivalents of 

 the Canadian Laurentian. 



2. The Huronian magnetic schists, quartzites slates and diorites- 



3. A great variety of rocks lithologically distinct, among which 

 are diabase, melaphyres, porphyries, conglomerates, shales and sand- 

 stones, known as the Copper Bearing Series. 



4. The Loimr Silurian Sandstones. 



Of these formations, the Laurentian and Huronian are not known 

 to occur in the vicinity of the St. Croix River. The first proba- 

 bl}^ will not be found nearer than twenty-five or thirty miles to the 

 St. Croix, while the existence of the second, as shown below, may 

 be proven much closer to that stream. 



1. Laurentian. — The rocks of this, the most ancient geological 

 age of which we have any knowledge, although ver}^ interesting to 

 the geologist, are in northern Wisconsin of comparatively little 

 importance. In this state we have no evidence of the occurrence 

 of usefal minerals in these rocks, in anything like workable quan- 

 tities. Gold, however, has been reported in very small quantities 

 from Oconto county. Professor Irving reports traces of gold 

 and silver in quartz from Clark county, which is probably of this 

 age. The Laurentian rocks are usually granites, passing tnrough 

 the fine and medium grained to very coarse grained varieties. 

 Rocks of this age, with a single exception, were found to occur the 

 entire distance passed over in the reconnaissance of the Chippewa, 

 Wisconsin, Pelican and Wolf Rivers. Upon the Chippewa and 

 and Wisconsin Rivers, numerous exposures of syenitic and horn- 

 blende rocks occur interstratified with granite aud gneiss rocks. 

 The bedding of the strata along these streams can usually be deter- 

 mined with a great degree of certainty. A remarkable uniformity 

 in the strike of the rocks of this region has been proven to exist. 

 There is scarcely an exposure along the banks of the Chippewa or 

 Wisconsin upon which the strike can be made out, that does not 

 fall within the arc included between north sixty degrees east and 



