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, 3Iadison: 



Ft. In. 



I. Heavy-bedded, jointed Mendota limestone (634), having a brown color, and 



close-grainod, 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 greensand layer 1 



III. Upper layers of Poisdam 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; scoUthxis-haaxmg 31 . . 



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

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

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

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

 record of a vreU near by: 



LOWER MAGNESIAJSr. 



Ft. 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-yeUow-mottled, porous limestone (603, 611-), with large patches 



of rhombohedral calcite, much dendritic manganese oxide, 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 hme (606) and containing only 2.3 per cent, of insoluble 



ingredients ' 8 



5. Layer of ooKtio chert (608); a milk-wliite material made up of httle con- 



eretions j'j to ^V inch in diameter, which consist of minute rounded grains 

 of hmpid 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=100.15; thickness, one inch to 6 



MADISON. 



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



green grains of glauconite . , \ g 



7. Light buff-colored sandstone (604); m heavy uniform layei-s six inches to 



two feet in tliickness; much used as a buUdmg stone in Madison: con- 

 tains 10' per cent, of carbonates of Hme 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 brovm sandstone in well I4 



mendOta. 



11. Hard yellow limestone, in weU 3q 



POTSDAM. 



12 Soft greenish sandstone, in well 20 



107 .. 



The building stone of these quamcs 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 -x 



