310 GEOLOGY OF EASTERN WISCONSIN. 



miles northward the change is slight. The rock becomes somewhat more firm, compact, 

 and serviceable as building material and of a gray or blue cast rather than buff. It is 

 also somewhat more argillaceous. 



In the vicinity of Fox Lake and at Waupun, this change has become quite pro- 

 nounced, resulting in a rock, much superior to that farther south, for purposes of con- 

 struction, though less serviceable for quicklime. If the formation be traced along its 

 western margin, that is, along its base, the modification of its characteristics is found to 

 be very gradual. Along the upper margin, there are but few opportunities for ex- 

 amination. 



At Seven Mile Creek there is a flat weathered exposure that reveals little, save the 

 fact of change in the direction indicated. Moore's quarry in the western part of the city 

 of Fond du Lac displays a rough, coarse, thick bedded rock of irregular texture, con- 

 taming cavities lined with calcite and pyrite, and somewhat, though not remarkably, ar- 

 gillaceous. While different from the rock at Watertown and southward, it still retains 

 a noticeable resemblance to it. Beceptaculites Oweni and Murchisonia bellicincta (major) 

 occur here, as well as at Waupun and other points in this region, and leave no doubt as 

 to the horizon to which these beds belong. At Moore's quarry the strata have been 

 forced up into a sharp anticlinal axis, from which the beds dip equally in both directions 

 at an inclination of upwards of 10. The trend of the axis is northwest and southeast. 

 It is manifestly a case of disturbed strata, but the extent of the distubance is unknown, 

 as the excavation is very limited. It is interesting chiefly because such features are 

 very rare in this quiet region. While sloping and undulating beds are not at all un- 

 common, they almost invariably carry with them evidences that they were so deposited 

 rather than folded or tilted by subsequent force. 



Beyond this point, so far as known to me, the Galena formation has not been mapped 

 by previous investigators, and most, if not all of the rocks north of this point, now re- 

 ferred to that horizon, have heretofore been placed either in the Trenton series below, or 

 the Cincinnati above, and lest the position now taken should be misapprehended, it 

 must be borne in mind, that it is simply claimed that the beds in question belong to the 

 Galena horizon, and are a continuation of the unquestioned strata of that formation as 

 found to the southward, and since they are the exact stratigraphical equivalents of the 

 lead-bearing beds, they are mapped and described as being a modified form, of that sub- 

 division of the Trenton group. Whether the term Galena limestone should be applied 

 to this group of strata as far as they are directly traceable, or whether it should be lim- 

 ited to the lead-bearing portion, or whether it should apply to that portion which has 

 the same lithological character as the lead-bearing portion, but is not itself productive, 

 as for instance, that portion now described, or whether it should be extended as far as a 

 similarity of organic remains is found, which would include a portion whose lithoiogical 

 characters differ from the typical Galena limestone, is not here discussed, and is a mat- 

 ter of little practical importance, except as a means to a clear understanding of the facts. 



But it is a matter of much importance to ascertain precisely what becomes of the lead- 

 bearing formation as it recedes from the productive area in southwestern Wisconsin, 

 since it adds to our knowledge of the conditions under which the formation had its 

 origin, and which, it is commonly held, determined its metalliferous character. About 

 two miles southwest of Oshkosh are quarries that possess unusual interest, on account 

 of their relation to this qiiestiou. Two kinds of rock are displayed by the excavations. 

 The lower portion, consisting of an exposure of 15% feet, is formed of regular, uniform 

 layers from 4 to 10 inches in thickness, rarely more or less, of a crystalline, compact, 

 hard, brittle, subtranslucent, magnesian limestone, marked at intervals with irregular 

 argillaceous seams of a deep blue color, occasionally tinged with green. These shaly 

 partings are usually clustered about the bedding joints, to which they probably stand in 

 the relation of cause. Aside from these seams, the mass of the rock is a dark bluish 



