604 GEOLOGY OF CENTRAL WISCONSIN. 



The following is the section at MacBricle's point, on the north shore of Lake Mendo- 

 ta, N. W. qr. Sec. 1, Madison: 



I. Heavy-bedded, jointed Mendota limestone (684), having a brown color, and 



close-grained, flinty matrix, and leaving on solution 15.05 per cent, of a 

 fine sandy residue; layers run 2 to 4 feet in thickness; joints N. 87 W., 

 used in construction of old capitol at Madison 21 8 



II. Thin- laminated yreensand layer 1 



III. Upper layers of fotsdam sandstone; fine-grained, light-greenish-tinted, 



calcareous sandstone, containing 15.5 per cent, of soluble ingredients; 

 thin-bedded, alternate layers, different colors; some more calcareous 

 layers weathering in relief; scolithus-bvaring 31 



On the N. W. qr. Sec. 21, and the N. E. qr. Sec. 20, Madison, is a round isolated hill 

 capped by the Lower Magnesian. The top of the hill is almost completely encircled by 

 a large quarry which exposes the Lower portions of the Lower Magnesian and the upper 

 part of the Madison sandstone. The following section includes the quarry face and the 

 record of a well near by: 



LOWER MAGXESIAN. 



Fl. In. 



1. Yellow, fine, granular, close textured limestone (607); thin bedded to 



shaly; some few layers near the top are burnt for lime 5 8 



2. Gray-and-yellow-mottled, porous limastone (603, 611-), with large patches 



of rhombohedral calcite, much dendritic manganese oxi:le, and 4.1 per 

 cent, insoluble matter; forming one layer 2 



3. Thin-bedded to shaly yellow limestone, mostly quite sandy 10 



4. Layer burnt for lime (606) and containing only 2.3 per cent, of insoluble 



ingredients , 8 



5. Layer of oolitic chert (608); a milk- white material made up of little con- 



eretions -fa to T V inch in diameter, which consist of minute rounded grains 

 of limpid quartz encased in a milk- white powdery matrix; having the fol- 

 lowing composition : silica, 98.01; alumina, 0.53; iron sesquioxide, 0.73; 



lime, 0.67; magnesia, 0,21=100.1i>; thickness, one inch to 6 



MADISON. 



6. Greensand layer, consisting of a matrix of rounded quartz- grains and dark 



green grains of glauconite . , 1 6 



7. Light buff-colored sandstone (604); in heavy uniform layers six inches to 



two feet in thickness; much used as a building stone in Madison: con- 

 tains 10 per cent, of carbonates of lime and magnesia 12 



8. Light-colored sandstone, similar to the foregoing but less firm and regular; 



in the lowest portions at the base of the quarry a loose white sand ... 5 8 



9. Unexposed, below the quarry base 5 



10. Soft red and brown sandstone in well 14 . . 



MEXDOTA. 



11. Hard yellow limestone, in well 30 



POTSDAM. 

 12 Soft greenish sandstone, in weh 1 20 



107 .. 



The building stone of these quarries is much sought for. It is obtained also from 

 quarries across a small valley, on the N. W. qr., Sec. 21. It was formerly worked to u, 



