680 GEOLOGY AND TOPOGRAPHY OF THE LEAD REGION. 



most extensive quarry that has been opened any where in this forma- 

 tion. It is the property of Mr. Wm. T. Plenry, of Mineral Point, by 

 whom it was opened in the summer of 1872. The stone in this quarry 

 is of two colors, both a very dark red, but one somewhat lighter in 

 color than the other. It very closely resembles the Lake Superior 

 sandstone in color, and is by far the handsomest building stone that 

 has come under our observation in the Lead region. The railroad 

 passes through the hill, so that the stone can be loaded directly from 

 the quarry on the cars.' 



TRENTON (BUFF AND BLUE) LIMESTONES. 



Geographical Boundaries. It will not be necessary to enter into 

 a detailed description of the ground covered by this formation. It is 

 sufficient to say that it is always found between the lowest bed of the 

 Galena limestone and the top of the St. Peters sandstone, and having 

 an average thickness of about fifty feet. 



Lithological Characteristics. The Blue is remarkable as being 

 the purest limestone in the Load region, and the nearest approach to 

 the Trenton, limestone of the eastern states, both in its lithological 

 and paleontological characteristics. A very noticeable feature is its 

 marked division into two parts; one very heavy-bedded, in layers of 

 two or three feet thick, known as the glass rock, whicb constitutes the 

 lower half; and the other, thin-bedded, in layers of two or three 

 inches, graduating sometimes without much change into the thin- 

 bedded Galena limestone above. It is at this point that the stratum 

 of carbonaceous shale occurs, which is the line of demarkation between 

 the Blue and Galena limestones, and as such, is an unfailing guide. 

 It varies very much in its thickness, being from a quarter of an inch 

 to a foot or more, but wherever a good exposure of the two formations 

 is seen, it has uniformly been found. 



The carbonaceous shale attains its greatest thickness in the vicinity 

 of Shullsburg. At the Oakland level on the S. W. qr. of Sec. 5, T. 

 1, E. 2 E., it varies from one to two feet; ^ and at the grounds of the 



'The following is an analysis of this stone, by Mr. E. T. Sweet: 



SUica 96 . 74 



Alumina 71 



Sesquioxide of iron 1 .45 



Carbonate of lime 1 .24 



Carbonate of magnesia 18 



100.32 

 'Prof. W. W. DanioUs, of Madison, has made the following analysis of the shale: 

 carbonaceous matter, 43.60; carbonic acid, 0.88; water, 0.30. 



