ANNUAL REPORT FOR 1875. 7f 



It is an important fact, that Mr. Wright found, by microscopic ex- 

 amination, the crystalline structure of the Penokee rocks, to be meta- 

 morphic and not igneous. His authority on this point is conclusive. 



Whether the Huronian formation of the Penokee mountain extends 

 westward to the St. Croix river, is a question of great interest, both 

 in the scientific and economic geology of Wisconsin. Awaiting de- 

 ductions from more detailed examination to be made by the survey in 

 1876, the undersigned may here give the arguments in favor of such 

 a conclusion, taken from the report of Mr. Sweet, who has had more 

 experience in this part of the state than any other member of the 

 geological corps: 



" I. The westward extension, and occurrence on the St. Croix river, 

 of all the formations in their regular order, except the horizontal sand- 

 stone formed north of the Penokee range, is a strong argument from 

 analogy. We can not expect to find as well defined ridges nor as 

 high ranges near the St. Croix as there are in the eastern part of Ash- 

 land county, for the dip of all the formations gradually decreases to- 

 wards the west. The dip of the Huronian schists at the gorge at 

 Tyler's Fork is 75 to the northwest. At Penokee Gap it is 66, and 

 at a point near Atkins Lake only 45 in the same direction. The 

 conglomerates and sandstones, which have nearly a vertical dip to the 

 northwest at the mouth of the Montreal river, and the mouth of 

 Tyler's Fork, have but a slight dip on the St. Croix river. At Lc- 

 high's on Bad river, the southward dipping sandstones have a dip of 

 38 to the southeast; at Wilton's the dip is 26; at the St. Croix only 

 14 to the southeast. 



" II. If the Iron-bearing belt extends westward as far as the St. 

 Croix, it doubtless follows the southern boundary of the Cupriferous 

 formation. It would, therefore, intersect the river some distance below 

 the mouth of Snake river. Then in the neighborhood of a line drawn 

 from Snake river to Penokee Gap, one would expect to find indica- 

 tions of the formation." 



Iron ore is reported, by explorers, to have been found in place, at 

 several localities in the vicinity of this line. 



Explorers report it from near the southern end of Long Lake, from 

 section 18, town 43, range 9 west, and from the northern part of Bur- 

 nett county. .Near the mouth of Wood river, on section 19, town 38, 

 range 19 west, are found on the original survey plat the signs used to 

 indicate rocks in situ, and the words "iron ore." 



" III. The occurrence of small angular boulders of magnetic rock 

 and iron ore, in the drift at numerous localities in Polk and Burnett 

 counties," is another strong argument. 



