364 



GEOLOGY OF EASTERN WISCONSIN. 



m 



the layer above having changed so as to be scarcely distinguish - 

 able from the compact rock below. Farther on, the difference 

 becomes still less, a few cavities, and a slightly greater irregu- 

 larity in the subordinate layers, being all that distinguishes 

 them from the layers below, (h.) At the farthest point t:> 

 which these layers can be traced, no geologist would think of 

 separating them from the layers below, thus making it a clear 

 case of thinning out and transformation. These layers are es- 

 sentially horizontal. 



If we now return to the point in the southwestern part of the 

 quarry, whence we started, and take 69 paces to the southwest, 

 we find the rock exposed in the road as f ollows : 



First, a compact limestone, similar to that in the quarry, dip- 

 ping eastward at an angle of 6. The upper layer is 8 inches 

 thick, underlaid by one of 4 inches, (d.) The rock for 5 paces 

 is then covered, beyond which it again appears. The upper 2'2 

 inches of this are divided irregularly into beds, the superior por- 

 tion of which is as compact as any seen at the quarry, but the 

 lower is somewhat more porous. This dips 11 N. of E. Under 

 this lie 5 niches of porous rock, but not of the most pronounced 

 class. Under this, again, He 2 inches of similar kind; beneath 

 which, again, there are 5^ inches of limestone, containing 1 

 ]r,any cavities of the size of an almond, and similar to the upper 

 layer described at the quarry. Under this he 18% inches of the 

 more pronounced and typical, porous, granular rock, (c.) Hero 

 again the section is interrupted by 8 paces of unexposed surface, 

 when a porous, granular rock succeeds, having a dip of 14 N. 

 of E. (6.) There are about 26 inches of this, the irregularity of 

 the structure making it difficult to measure exactly. Below this 

 come 6 to 8 inches of a rough, irregular, brecciated, rather 

 hard and tough, but somewhat porous, rock, containing large 

 and small crinoid stems, like those common in the Racine beds. 

 The section is again interrupted for 4 paces, when a rough, very 

 irregular, brecciated, porous rock follows, constituting a confused 

 mass, similar to the rock mounds near Milwaukee and Wauwa- 

 tosa, yet to be described, (a.) In this, Illcenus ioxus, fragments 

 of Atrypa and Rhynchonella, crinoid stems, and an Orthoceras, 

 were found. This exposure continues 18 paces. The whole sit- 

 uation is imperfectly represented by the accompanying figure. 



It seems to be possible to draw but one rational conclusion 

 from the foregoing facts, viz: (1) That the last mentioned irreg- 

 ular mass stood as a reef in the depositing sea; and (2) that the 

 alternating layers were deposited on its slope, while (3) these, 

 in the more quiet waters at a little distance from the reef, were 

 replaced by a deposit of finer silt, which formed the compact 

 layers. The unusual phenomena of cross and oblique lamina- 

 tion in limestone harmonizes with this view. 



Within a mile from this point, there are several exposures of 

 the compact rock. In the south half of Sec. 36, this even tex- 

 tured, compact variety is associated with a layer of the same 

 general color and composition, but having a sort of lumpy 

 structure, a kind of conglomerate, in which the pebbles and 



