264 GEOLOGY OF EASTERN WISCONSIN. 



stone in Wisconsin has the general form of a crescent. "We have the 

 right or eastern horn of this crescent under consideration. It enters 

 the district obliquely from the soiithwest, and occupies the western 

 margin of Green Lake, Winnebago and Outagamie counties, from 

 whence it extends to the northeastward, passing into Michigan across 

 the upper great bend in the Menomonee river. It is much narrower 

 in this than in the central portion of the state, averaging only from 

 ten to fifteen miles in width. The formations in this part of the 

 state have a rudely zigzag or stair-like outline, in which this sand- 

 stone participates. This is more especially true of its upper limit or 

 eastern boundary, where it is overlaid by the Lower Magnesian lime- 

 stone. Its lower limit cannot be mapped with equal precision, owing 

 to the unevenness of the underlying formation and the ever present 

 obscuring drift accumulations. Beyond the limits marked on the 

 maps, where detailed investigations have not yet been made, isolated 

 patches will doubtless be found resting upon the Archaean rocks. 



A more clear and accurate view of the surface extent and location 

 of this rock than it is possible to convey by verbal description, may 

 be obtained by consulting the accompanying maps, to which the at- 

 tention of the reader is respectfully invited. 



The formation dips to the east, and passes under all the formations 

 lying in that direction, as shown in the sections on the accompanying 

 maps, and in this volume under the head of Artesian Wells, so that 

 it underlies at varying but ascertainable depths the whole of the east- 

 ern part of the state. 



SECTIONS AND LOCAL DESCRIPTIONS. 



The township of Kingston in the southwest comer of Green Lake county, being the 

 most southerly town in the district under consideration that is occupied to any extent 

 by this formation may serve us as a suitable point whence to proceed northward in sketch- 

 ing such local developments of this formation as may seem to demand notice, the more 

 iittingly so because it presents several prominent elevations that expose the formation. 

 The most satisfactory of these is Bartholomew's Bluff, iu sec. 15, S. hf of N. E. qr., T. 

 14, R. 11 E. This hUl is conspicuously terraced, the lower shelf being capped by the 

 Mendota beds and the upper by the more enduring Lower Magnesian limestone. The 

 sandstones that form the rest of the hill, being soft, have been more affected by erod- 

 ing agencies, leaving limestone-capped benches as seen in the accompanying figure. 



The following is the section exposed at this point, in descending order: 



1. Bluish-gray, thick bedded, sub-crystaUine, sUghtly sihcious dolomite, uneven tex- 

 ture, granular in part, compact in part, and approaching a brecoiated structure in por- 

 tions, weathering to a rough ragged aspect; fossils absent or very rare; the bottom lay- 

 ers of the Lower Magnesian limestone, not completely exposed but probably about 20 

 feet in thickness. 



2. Slope of the terrace, concealed by debris; known to be occupied in part at least by 

 a yellowish quartzose sandstone, with slight calcareous cement. It is probable, from ob- 



