GEOLOGICAL FORMATIONS. 681 



Silvertliorn mine on the JS". E. qr. of Sec. 31, T. 2, R. 2 E., it has a 

 thickness of seven feet, 1 affording in each of these localities small but 

 handsome crystals of Galenite, having smooth polished faces, which 

 is but seldom the case with crystals of this mineral found at other lo- 

 calities in the Lead region. 



The following section taken from the Darlington quarry will give 

 a good general idea of the formation. The quarry is situated on the 

 N. E. qr. of Sec. 3, T. 2, R. 3 E.: 



Galena Limestone. 



Ft. In. 



1. Soil and loose rock 2 



2. Yellowish, hard, compact dolomite, similar to the Buff on the surface, but 



not blue between the layers, evenly bedded in layers one foot thick 6 



3. Thin layers two to four inches thick 5 . . 



4. Carbonaceous shale 2 



Blue Limestone. 



5. Thin-bedded, very fossiliferous limestone, in layers from two to five inches 



thick 3 6 



6. Heavy-bedded, dark blue limestone, very hard and compact, unfossiliferous 



except in the shaly partings between the beds 2 12 . . 



Buff Limestone. 

 1. Heavy-bedded, light blue limestone, weathering to buff on exposure; beds 



from 4 to 6 feet thick, contains but few fossils, quarry rock 32 



8. Thin-bedded, fossiliferous limestone, similar to preceding 13 . . 



9; Unexposed beneath bed of river not less than 10 



Total thickness 83 8 



The Blue limestone has here a thickness of fifteen feet and six 

 six inches, and the Buff not less than fifty-five feet, which is remark- 

 able as being much greater than was seen at any other point. Its av- 

 erage thickness does not exceed thirty feet. 



1 Also the following analysis of the Silverthorn shale: 



(1) Carbonaceous matter, 18.31; carbonic acid, 1.85; water, 0.40. 



(2) Carbonaceous matter, 15.76; carbonic acid, 0.60; water, 0.32. No. 1 of the Sil- 

 verthorn shale was quite dark colored, while No, 2 was a light, ash-colored shale. 



The specimen from Oakland had been for several years exposed to the weather. 



2 The following is an analysis, by Mr. E. T. Sweet, of the Glass rock from Mineral 

 Point, corresponding to No. 6 of the above section: 



Silica 6 . 160 



Alumina 2.260 



Sesquioxide of iron 950 



. Carbonate of lime 85.540 



Carbonate of magnesia 3. 930 



Water 930 



Phosphoric acid 055 



99.875 



