318 GEOLOGY OF EASTERN WISCONSIN. 



rhynchus, Leptwna sericea, Rhynchomlla capax, and a new species, R. perlamellosa. 

 Beneath the ledges in this region, the Cincinnati beds approach near the surface, but 

 are rarely exposed on account of their soft nature. It is to this fact, chiefly, that the ver- 

 tical ledges owe their origin. The soft clays and shales were easily carried away during 

 the drift period, leaving the firmer Niagara limestone prqi'ecting above. Since the drift 

 period, the springs that issue so numerously at the surface of these clays have worn 

 them away stiU farther, and the Hmestoue from above has fallen in huge blocks and cov- 

 ered the slope at the base of the cUff. So that not only in the region we are now 

 speaking of, but for a hundred miles northward, the Cincinnati formation will chiefly 

 manifest itself by a slope, covered with debris, at the base of vertical walls of hmestoue, 

 known in all this region as " The Ledge." Occasionally streams cut through this loose, 

 conceaKng material, and display portions'of the formation. An interesting case of this 

 kind occurs in the town of Herman, where a beautiful brook tumbles over the step- 

 like layers of Niagara limestone, and finally plunges into a gorge excavated from 

 the shales under consideration. Only a few feet of blue clay and a yellow arenaceous 

 shale are, however, exhibited. A similar instance occurs in the N. W. qr. of Sec. 21, 

 Taycheedah. The faUs at this point wash out of the clay large numbers of aggrega- 

 tions of crystals of iron pyrites. These n,re usually globular, but sometimes take varied 

 and fantastic forms. A considerable deposit of travertine, of modem origin, occurs at 

 this point. 



South of Clifton, on the east side of Lake Winnebago, upwards of 175 feet are oc- 

 cupied by this formation, above the level of the lake. How much it extends below is 

 not known. The upper portion is chiefly concealed with fallen blocks from the cKft 

 above and other debris. At the lake level there appears a dark chocolate brown shale, 

 alternating with impure limestone and shale of Kghter color. The dark shale contains 

 many comminuted fragments of Lingulas. 



Above this, lies a bed of limestone, about eight inches thick, of mingled crystalline and 

 earthy structure. Upon tliis, rests a dark chocolate brown, slate-Kke shale, splitting 

 with facihty into soft, brittle plates. Many water- worn fragments of this stratum aro 

 heaped up by the waves on the beach below, and present an exaggerated illustration 

 of the difference between the rounding effects of beach action and of running water. 

 In the former case, the effect of the waves is, to cause the fragments to move up and 

 down the sloping beach, and if they were originally flat, as in this case, their tendency 

 is to shde, rather than roU, and the result is a round, disk-like, but not globular, form, 

 and this is very markedly the case at this point. On the other hand, the effect of nm- 

 ning water is to roll, rather than sUde, the fragments, and hence, to produce spherical 

 pebbles. This distinction, may be studied with profit, in connection with the drift de- 

 posits. Above the slate-like beds, lies a yellowish gray shale of homogeneous, some- 

 what arenaceous texture, and having a conchoidal fracture, giving the rock the appear- 

 ance of having an obscure concretionary structure. 



Beds higher than these, and lower than those previously described, are shghtly ex- 

 posed in Lot 59, Stockbridge, where shales and limestones constitute the section and Orthis 

 oecidentalis, 0. tricenaria, Strophomena alternata, and Ehynchonella capax, the chief 

 features of the fauna. An extraordinarily large specimen of the last named species was 

 found, by Mr. King, at this locality. In Brown county, several of the streams that 

 come down from above the ledge denude, to some extent, the Cincinnati beds. One of 

 these forms the beautiful Cascade Falls, east of De Pere, where the shales underhe the 

 iron ore deposit, and will be again mentioned in connection with that formation, and 

 another, east of Green Bay, forms a succession of rapids over greenish blue shales and 

 limestones. 



On reaching Green Bay, the formation is better exposed in its upper portion, but its 

 base here, as elsewhere, is concealed. The escarpment of limestone that forms Whit- 



