239 



Formation No. 3. — Hornblendic. 

 Compact, sub-crystalline and slaty ; black or dark colored ; 



strike N. 60° E. ; thickness on trail . . . . 2| miles. 



Formation No. 4. — Silicious, two members. 



a. Quartz, slaty and in layers ; dark colored, but less 

 than F. 3 ; thickness variable ; separated from 6 by a 

 bed of magnetic iron and iron slate. 



b. Quartz, slaty, in layers and beds ; more compact and 

 lighter color (gray and straw color) than a ; novaculite ; 

 strike N. 60° to 65° E. ; dip variable, 30°, 45°, 60°, 75° 



to the northwest ; breadth across the edges on trail, 3^ miles. 



Formation No. 5. 



Granites and sienites of Central Wisconsin, 



Fifteen miles to the westward of the trail, on a parallel line from 

 the mouth of Tyler's Fork to the Dalles, the total thickness of forma- 

 tions 2, 3 and 4, is reduced nearly one-half. The diminution, how- 

 ever, comes principally from the upper member, a, of formation 2, 

 which tapers out in that direction very rapidly. Formation 3 is also 

 somewhat diminished ; yet formation 5 is not materially changed in 

 thickness. 



Further westward, beyond the middle or main fork of Bad Eiver, 

 the rocks undergo such changes in external characters, that until the 

 test of analysis was applied, the separate formations could not be dis- 

 entangled. In the midst of black slates that appeared to be trachytic, 

 were large patches of red and blue crystalline rocks, having clearly 

 the aspect of sienites. I will notice them hereafter. 



Formation 1 is nearly pure silex, and is evidently of sedimentary 

 origin. Some foreign geologists have essayed to place it nearly at the 

 summit of the geological system, not only without evidence, but against 

 the most conclusive proof. Dr. Houghton, Dr. Jackson and Dr. Owen 

 at first lent color to such a classification, but on examination both the 

 first and the last named gentlemen placed it in its true position, at 

 the base of the paleozoic rocks. It has been traced stratigraphically 

 beneath the Trenton and calciferous strata of the New York Survey ; 

 on the St. Mary's River at the Pictured Rocks ; on the Escanawba, 

 the Menominee, Oconto, Wolf, Wisconsin and St. Croix Rivers. 



At the falls of the St. Croix abundance of fossils are found in it, 

 such as characterize the Potsdam in New York. To persist in deny- 

 ing the effect of such observations is to rob all proof of its value, 

 when it comes in contact with theory and assumption. 



The black slate intercalated with the sandstone differs little exter- 

 nally from the slaty portions of formation 3. This member is very 



