276 GEOLOGY OF EASTERN WISCONSIN. 



could be detennined, was quaquaversal, being greatest on the sides and perceptibly less 

 at the extremities. Tlie greatest dip observed in this vicinity was 20°. In most cases 

 apparently only the crest of the arch was exposed and the dips were low. 



One of these hills, situated near the center of the east line of section 1.5 of the town of 

 Winneconue, presents some special features deserving mention. The uppermost layer, 

 where still preserved, contains a large ingredient of quartzose sand, or is incrusted with 

 sand, or in other cases, consists of a conglomerate or breccia whose matrix is quartzose 

 sand. This layer is also sometimes oolitic. As similar facts were observed at several 

 other widely separated locaKties, this sandy portion is behoved to be the transition layer 

 to the St. Peters sandstone, and if so, it indicates, where preserved, the original form 

 of these mounds, and that in these instances the drift forces have only removed the in- 

 coherent sandstone above. This is rendered the more probable by the fact that usually 

 this sandy layer was found on the southwest-ward side of the prominence, where it would 

 be protected from the more forcible action of the glacier, while the northeastern comer, 

 which sustained the fuU force of the ice mass coming from that direction, was often con- 

 spicuously abraded. 



Another interesting fact observed at this point was the presence of distinct mud- 

 cracks and ripple marks. The latter are far less common on hmestone than on sand- 

 stone, and the fonner are more abundant in shales. Both occur here together on the 

 gentle slope of one of these pecuhar mounds. TJie dip, here, varies from to 8°, con- 

 fonning as usual to the shape of the hill, which in tliis case departs somewhat from the 

 usual, symmetrical contour. The rock structm-e is very UTegular. Some portions are a 

 well marked conglomerate, both matrix and pebbles being, however, dolomitic. A layer 

 near the surface is very fossihferous, over the small space exposed, but the casts are so 

 obscure as to preclude satisfactory specific determinations. They consist of the internal 

 casts of an Ophilefa and two undetermined species of Eaphistoma. 



While our attention has thus been fastened upon the pecuharities of the superior face 

 of the Lower Magnesian formation, we have been led northward along the eastern mar- 

 gin of the outcrop, where alone the upper portion has escaped erosion, and have passed 

 by some noteworthy outcrops belonging to the middle and lower parts of the formation. 

 If we now return to the vicinity of the village of Eureka we shall be introduced to a 

 feature that characterizes the snbmedian portion of the formation. The ledge south- 

 west of that plp.ce presents the following section in descending order : 



1. Heavy irregular beds of impure dolomite, containing many cavities, more or less 

 filled with quartz crystals of the transparent and milky varieties; texture varying; bed- 

 ding uneven and somewhat undulatory; rock weatliers to a very rude ragged aspect. 

 Thickness, 10 feet. 



2. Eeddish shale, variegated vrith gray and green, the lower portion mostly soft, break- 

 ing and crumbling easUy; some parts quite arenaceous; the upper portion more calcare- 

 ous or dolomitic, and containing many aggregations of quartz crystals, usually of the 

 opalescent variety. The layers are irregular and somewhat undulating. Thickness, 15 

 feet. 



3. Very heavy beds, nearly unifonn in thickness, and horizontal in bedding. Tlie 

 rock contains many almond-sized but UTegular cavities, only a small proportion of which 

 are filled with crystals. It is imeven but distinctly granular crystallme in texture, me- 

 dium in hardness, and dhrty gray or buff on the exterior, but mottled bluish on the in- 

 terior. It is well adapted to heavy masonry, as foundations, piers and locks. It 

 is used for the latter purpose in the construction of the adjacent locle on the Fox river. 

 Tliiokness exposed, 6 feet. 



Attention is here called to the shale which constitutes the middle member of the sec- 

 tion. What appears to be the stratigraphioal equivalent of this, occurs at several points 

 to the northward, the most remote being over one hundred miles distant. From this 



