560 GEOLOGY OF CENTRAL WISCONSIN. 



definitely an alternating series, all the beds of which are mao-nesian. 



.- ~ O 



This succession, beginning below, is as follows: Lower Buff (the 

 "Buff" of the Lead Region), dolomitic, 23 feet; Lower Blue, also 

 magnesian, 23 feet; Upper Buff, dolomitic, 55 feet; Upper Blue, 

 also magnesian, 15 feet. Only the two lower ones of these are ordi- 

 narily seen in the Dane county quarries. 



The Buff (or Lower Buff) limestone is a very evenly bedded, bluish 

 to buff-colored, close-textured dolomite, in layers from a few inches 

 to 2 or 3 feet in thickness. Externally the layers are usually a 

 brighter yellow than within, owing to a partial peroxidation of the 

 iron-protoxide contained in the rock. The following analysis is one 

 from the Buff layers only a short distance below the junction with the 

 Blue, from Earth's quarry, in the southern part of the town of Bris- 

 tol, Dane county: 



Carbonate of lime 56*07 



Carbonate of magnesia , 35.32 



Silica 4.45 



Alumina 2.08 



Iron sesquioxide 69 



Iron protoxide^ 58 



Water.. .46 



99.65 



In the upper part of the Buff' limestone, purplish-brown, close- 

 textured, conchoidal-fracturing layers occur, which contrast much 

 with the remainder of the stratum. The Buff limestone yields a good 

 building stone and is very frequently quarried. 



The Blue (Lower Blue) is to be seen ordinarily only in its lower 

 half, 2 to 10 feet of which are not unfrequently laid bare in quarries 

 on the Buff beds. These lower layers are very thin, nodular- surfaced, 

 and made up of dark bluish-gray, flinty-textured limestone, in which 

 small specks and strings of calcite are thickly scattered, and in which 

 also numerous fossil fragments are imbedded. Included between 

 these layers are seams of a very thinly and regularly laminated, dark 

 brown, fragile, calcareous shale, showing numerous black graptolite- 

 like markings. Of the following analyses of the Blue limestone, No. 

 I is of rock taken from the same locality as the Buff, of which an 

 analysis has just been given, and nearly at the junction of the two. 

 Of the other analyses, added for comparison, No. II is cited from the 

 report of Mr. Moses Strong on the lead region, and is from Sec. 36, 

 T. 5, R. 2 E., whilst No. Ill is of Blue limestone from near Benton, 

 on the Fever river, and is cited from J. D. Whitney's report on the 

 lead region: 



