GEOLOGICAL FORMATIONS. 



673 



FIG. 5. 



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, K. 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 1 with some arenaceous 

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

 ness, which were noticed in 

 the valley of Grant river, in 

 the E". W. qr. of Sec. 22, T. 

 4, R. 4W. They were also 

 seen on Pigeon creek, near 

 the center of section 24, in 

 the same township; also in 

 the quarry at Reese's Mill, 

 in the N. E. qr. of Sec. 34, 

 T. 4, R. 4 E., in nearly the 

 same geological position, 

 near the top of the forma- 

 tion. 



They were not found oc- 

 cupying this position in 

 other localities. Their pres- 

 ence is due, probably, to 

 local causes alone, and they 

 cannot be considered as 

 constituent beds of the for- 



SSCTION OP CALCAREOUS AND ABENACEOUS SHALES AT 



GRANT KITKB. 



1. St. Peters sandstone. 2. Turfed slope. 3. Lime- 

 stone bed. 4. Calcareous shales. 5. Limestone bed. 6. 

 Calcareous and arenaceous shales. 7. Lower Magnesian 

 limestone. 



1 The following is an analysis of the calcareous shales, by Mr. E. T. Sweet: 



Silica 17.03 



Alumina 3 . 56 



Sesquioxide of iron 1 .51 



Carbonate of lime 42.14 



Carbonate of magnesia 34.56 



Water 1.28 



100.08 



Wis. SUR. 43 



