l6o LOWER PENINSULA. 



under which the slate rock is found, and upon the quality of the 

 rock as a roofing material. I spent in all two weeks on the excur- 

 sion ; therefore it can not be expected that I will give an exhaus- 

 tive report on the complicated geological structure of this country, 

 full as it is of upheavals. Yet I will endeavor to make a general 

 statement covering all important facts connected with the distribu- 

 tion and qualities of this valuable rock species. 



Let me here acknowledge the kind assistance received on this 

 occasion from Mr. S. C. Smith, a gentleman favorably known for 

 a great many years back as one of the most successful explorers of 

 the Lake Superior country. He accompanied me on the excur- 

 sion, and, aided by his minute acquaintance with the district, in 

 which he had spent the whole previous season in explorations, I 

 was enabled to see, during the short time at my disposal, nearly 

 all the more important outcrops dispersed throughout its dense 

 forests. 



Glancing over the geological map of the Lake Superior district, 

 issued with the report of 1873 on the Northern Peninsula, we see 

 the area of the Huron mountains, which attain an elevation of about 

 1200 feet above the lake, represented as composed of the Lauren- 

 tian rock series, rpainly crystalline, granitic and dioritic, massive, or 

 with obscurely stratified structure. 



On its northern margin, at the foot of the mountains, which 

 reach close up to the shore, this granitic rock series is surrounded 

 by a narrow belt of horizontal strata of the Lake Superior sand- 

 stone, inconformably abutting against it. Southward, nearly reach- 

 ing up to the highest crest of the mountain range, the Huronian 

 rock series leans inconformably against it, with its uplifted beds, 

 alternating between Slate rock, Quartzites, Diorites, and Jaspery 

 strata, interstratified with heavy seams of iron ore in the form of 

 magnetite, or as a red or brown iron oxide. These latter two are 

 designated by the miners as red and brown hematite. 



The western and northwestern slope of the granitic knot is sur- 

 rounded by slates which belong likewise to the Huronian series, 

 but differ from the slates of the Marquette district. It is not as yet 

 clearly ascertained what position this slate occupies relative to the 

 iron-bearing series. 



The slate rock extends, at the head of the Bay of L'Anse, close 

 to the shore, the outer edge of the shore line being formed by hor- 



