362 GEOLOGY OF EASTERN WISCONSIN. 



slialy partings or laminae of clay, so that the dripstone arc comparatively free from thcj 

 marly or clayey matter common in quarries. This is only true of the lower layers that 

 have not been affected by inwashing from above, and by the immediate action of the 

 surface elements. 



The vertical joints are prominent, and in soma portions frequent, and are usually 

 smooth, and coated with calcareous and pyritiferous deposits. 



The rock is porous and geodif erous ; the former condition being largely due to crin- 

 oidal remains imperfectly preserved, and the latter perhaps in part to the same cause, 

 also, the portion removed being the calyx. The material filling the geodes is chiefly cal- 

 cite and pyrite, both of which appear in abundant and beautiful forms. The pyrite 

 takes the tabular form of crystallization to a large extent, and the calcite seems to pre- 

 fer the form known as dog-tooth spar. Crystals of this an inch or more in length are not 

 uncommon. 



The rock is quite brittle and sonorous, and presents a saccharoidal appearance on the 

 freshly fractured surface of the unweathered layers. A bluish green, argillaceous ma- 

 terial is found in obscure, irregular partings. 



In fossils, it is far less prolific than the rock at the Rapids. 



At the quarries belonging to Mr. Trimbone, in the town of Greenfield, Milwaukee 

 county, the rock is chiefly a light buff, porous, granular, brittle dolomite, rather soft, 

 and in some cases almost friable, and at points disintegrating to a calcareous sand. A 

 little calcite in crystals, but no pyrite was seen. The fracture is rough, but usually 

 along the line indicated by the application of the force, the manner in which the force is 

 applied, rather than the nature of the rock, determining the line of fracture. 



But in the southeastern quarry, the rock differs considerably from the rest, being 1 

 harder, finer, more compact, less brittle, and bluer. 



In general, the beds are from 1% to 3 feet in thickness, but readily split into thinner 

 layers. The beds, though in general regular and somewhat uniform, not unfrequently 

 thicken, and curve, or undulate. Indeed, the last feature seems to be a common char- 

 acteristic when any considerable area is considered, so much so as to render any attempt 

 to get the general dip, by local observations, utterly futile. These undulations are not 

 regular, nor do they present a system, as though due to some common cause, as contrac- 

 tion or upheaval, but are in a sense inharmonious with each other. The phenomenon 

 arises, doubtless, in irregularities of deposition, and not in subsequent folding or other 

 disturbance. A little careful study is decisive on this point. One of the clearest illus- 

 trations of this is to be found in the southeastern quarry, where the lower bedding joints 

 can be traced in a straight line beneath the apparent folding. The next ones are lost in 

 a thick unbedded mass, over which the upper layers pass on a considerable curve. 



Passing by the Milwaukee region for the moment, we find near Cedarburg and 

 Grafton, excellent examples of the irregular nature of this deposit. At the village of 

 Cedarburg, most of the rock is a soft, porous, granular, minutely crystalline, dolomite, 

 varying in color from white to light cream. Occasionally, cavities of the size of a 

 walnut or larger appear, but they are not frequent. The beds are from 2 feet to 4% feet 

 thick, but not well defined, nor are vertical fissures regular or prominent. The local 

 dip varies from l c to 3j/ in a southwesterly direction, but is changeable. 



Other portions are harder and more compact, some of which, however, when mined 

 back from the exposed surface, become softer and more granular, at variance with the 

 usual fact. 



A half mile to the east, near the center of Sec. 26, a very soft crystalline rock, called 

 sandstone, from its friable and granular nature, occurs, having a strong dip to the west- 

 ward. Following down the stream a short distance, we find a hard, brecciated and geodif- 

 erous rock of bluish cast without apparent stratification. 



This gives place almost immediately to a granular rock similar to the preceding, but 



