GEOLOGICAL FORMATIONS. 673 



The Lower Magnesian is a formation of extremely variable thick- 

 ness; the greatest known in the Lead region, is about 250 feet; this, 

 however, is seldom seen. The country in the vicinity of the above 

 section, and Sec. 20, of T. 11, R. 2 "W., are two instances where the full 

 thickness prevails. In ranges 4 and 6 E., south of the river, the forma- 

 tion is frequently as thin as one hundred feet, in some localities, and 

 in others, only two or three miles distant, it will attain double that 

 thickness. These sudden variations in thickness are due to an un- 

 conformability between the Lower Magnesian and the St Peters 

 sandstone, discovered by Prof. T. C. Chamberlin, and described in 

 another part of this report. 



The only change from limestone that was observed was some lay- 

 ers consisting of a very fine calcareous shale' with some arenaceous 

 layers and earthy matter interlaminated, about three feet in thick - 



ness, which were noticed ia 

 the valley of Grant river, in 

 the N. W. qr. of Sec. 22, T. 

 ■'^^^ 4, E. 4W. They were also 



seen on Pigeon creek, near 



2-- -....^ the center of section 24, in 



5 ^n^gi^l ^^^^ same township; also in 



^^ "" ~ the quarry at Reese's Mill, 



^ ^ ^ in the N. E. qr. of See. 34, 



s ^j Mffl^ T. 4, R. 4 E., in nearly the 



same geological position, 



^ ''^^^1 near the top of the forma- 



v^ggf^- tion. 



7 ^^^^^^^^^^. They were not found oc- 



^Bsstp^E^'^^^^^^^t cupying this position in 



Section OF Caioaeeous AND Aeenaoeous Shales at Otuer localities. IneirpreS- 



GEANTErrEB. ence is due, probably, to 



1. St. Peters sandstone. 2. Tarfed slope. 3, Lime- i„„„i „, „!„„„ A <.T,„„ 



. , . „ , ,, »T i T,io local causes alone, and tney 



stone bed. 4. Calcareous shales. 5. Limestone bed. 6. ' ■/ 



Calcareons and arenaceous shales. 7. Lower Magnesian cannot be Considered aS 



"'"'''°"'- constituent beds of the for- 



' The following is an analysis of the calcareous shales, by Mr. B. T. Sweet: 



Silica 17.03 



Alumina 3.56 



Sesquioxide of iron 1 .51 



Carbonate of Ume 42.14 



Carbonate of magnesia 34. 56 



Water 1-28 



100.08 

 Wis. Sub.— 43 



