308 t. e. savage alexandrian rocks of illinois and wisconsin 



Alexandrian Strata in Wisconsin 

 general statement 



The oldest division of the Silurian limestone in Wisconsin was referred 

 to by Chamberlin 3 under the name "Mayville beds" and has a thickness 

 of 100 to 175 or more feet. The present studies have shown that this 

 lowest division of the Silurian rocks of Wisconsin corresponds in time to 

 some portion of the Alexandrian series of Illinois and Missouri and to 

 some part of tbe Becsie Eiver formation of Anticosti Island. 



DESCRIPTION OF SECTIONS 



Almost the entire thickness of the Mayville limestone is exposed in an 

 abandoned quarry 3 miles south of the town of Mayville. A detailed 

 section of the rocks exposed in this quarry is given below : 



Section of Mayville Limestone exposed in a Quarry 3 Miles south of Mayville 



Feet 

 5. Dolomite, yellowish gray, vesicular, in layers 2 to 6 feet thick, which 

 contain very numerous casts and molds of shells of Yirgiana bar- 

 randei var. mayvillensis ' 21 



4. Dolomite, hard, yellowish gray, with many irregular cavities and a few 



casts of shells of Yirgiana barrandei var. mayvillensis 10 



3. Dolomite, massive, hard, crystalline, in layers 4 to 6 feet thick 33 



2. Dolomite, yellowish gray, fine-grained, in layers 4 to 16 inches thick... 32 

 1. Dolomite, hard, crystalline, in rather thick layers having numerous 



irregular cavities 22 



The upper 12 to 20 feet of the Mayville beds everywhere contain 

 numerous casts of shells of Virgiana barrandei var., which serve as an 

 excellent marker of this horizon in eastern Wisconsin. 



In the large quarry 4 miles south of Mayville the zone of Yirgiana 

 barrandei var. occurs about 50 feet above the base, and a drilling pene- 

 trated 90 feet of dolomite below the floor of the quarry without reaching 

 Maquoketa shale, indicating a thickness of at least 140 feet of Mayville 

 limestone below the Virgiana zone. 



The relation of the Mayville limestone to the older strata of this region 

 is well shown in the quarry face of the old iron-ore pit in Iron Ridge, 

 near the village of ISTeda, about 6 miles south of Mayville. The character 

 of these strata is shown in figure 1 and is described in the detailed section 

 given below : 



; T. C. Chamberlin : Geology of Wisconsin, vol. ii, 1877, p. 336. 



