554 GEOLOGY OF CENTRAL WISCONSIN. 



sandstone, has its base 40 to 60 feet lower than the exposures of Lower 

 Magnesian in the immediate vicinity. About Madison, in Danecoun 

 ty, the Lower Magnesian is only from 50 to 80 feet thick; just north 

 in the high prairie country on the borders of Columbia and Dane 

 counties, it has thickened to 125 to 140 feet, a fact in itself sufficient 

 to suggest the existence of an eroded upper surface. It is not improb- 

 able that some of the swells of this high region are directly due to 

 the irregular surface of the underlying limestone. 



The fossils of the Lower Magnesian are not common, and when 

 found are but obscure gasteropod and orthoceratite markings in the 

 chert of the uppermost layers. If the two small patches of limestone 

 already alluded to as occurring in the region between the quartzite 

 ranges of the Baraboo be regarded as belonging to this formation, 

 quite an interesting addition is to be made to the hitherto meager 

 list of Lower Magnesian forms. The limestone of one of these small 

 areas has yielded a number of fossils which are regarded bv Mr. R. 



t/ O t/ 



P. "Whitficld, as " certainly not lower than the Lower Magnesian," to 

 which formation the composition, lithological character, and position 

 of the rock would also refer them, the difficulty lying in the pecu- 

 liar conclusions that are thus led to with regard to the Lower sand- 

 stone in the vicinity, as explained on a previous page. These fossils 

 are: Stromatopora, und. sp. ; Orthis Barcibuensis? ; Ilolopea,, n. 

 sp. ; Maclurea Swezeyi, n. sp. ; Illcenus antiquatus, n. sp. ; Dicello- 

 cephaliis Barabuensis, n. sp.; D. Eatoni, n. sp. ; and triangular 

 sheath-like bodies. 



The economic contents of the Lower Magnesian are limestone for 

 burning into lime, and building stone. Galena, in small quantities, 

 lias been obtained from crevices in the Lower Magnesian, but the 

 only occurrence of this kind known in Central Wisconsin is that near 

 Doylestown, in Columbia county, where a limited crevice in the lower 

 part of the formation has yielded several hundred pounds of this ore. 

 This occurrence is interesting because at such a distance from the 

 productive lead region. I have seen no other indication that the 

 Lower Magnesian is ore-bearing. Lime is burnt from the Lower 

 Magnesian at a great many points, and from quite different horizons. 

 The lime produced is uniformly quite slow in slacking, making, how- 

 ever, a very strong mortar. It is rarely very white. Many of the 

 lower beds are too sandy for lime burning, the best for the purpose 

 being apparently the heavy grayish-white layers 40 to 50 feet above 

 the Madison sandstone. Twenty thousand bushels annually are burnt 

 from these layers, on Sec. 33, T. 7, R. 9 E., the product being widely 

 known as " Madison lime." The Lower Magnesian is in general too 



