LOWER MAGNESIAN LIMESTONE. 



275 



larity is unquestionably clue diiefly to the undulation of the upper strata of the foi-ma- 

 tiou; but there is evidence that the sides of these prominences were somewhat worn by 

 wave action daring the deposit of the St. Peters s,mdstone and a portion of the rook 

 incorporated in that formation. Near the west line of the township of Ripon, on the 

 lowlands, neai- the ledge that marlts the limit of the Trenton plateau, the upper por- 

 tion of one of these swells is iinely shown. It is only a few rods in extent, and attains 

 but a meager elevation compared with those just described. It is oval and symmetrical 

 in outline, and has its greater axis, which is about twice its transverse diameter, east 

 and west, in harmony with the general rule. The surface rock, which alone is exposed, 

 is rather even bedded and homogeneous for tliis formation, in which irregular structure 

 is the prevalent form. 



West of Rush Lake, at several points, the biUowy character of this face of the for- 

 mation is shown by variously dipping strata and half exposed domes of rook. 



In the railroad cut adjacent to the lake shore, near the center of section 15, Nepeuskin, 

 something of the nature of the interior of these mounds is revealed, though the cut does 

 not exceed six feet in depth. The surface of the rock is irregularly undulating, consist- 

 ing of hummocks and hollows; notwithstanding which, it is interesting to note that it 

 is poMehed and covered with glacial striae, bearing westward. It might be supposed 

 that the present surface is due to erosion, weru it not for a sandy layer, covering a por- 

 tion of the surface, that seems to belong to the sandstone subsequently deposited. The 

 rock is very irregular in bedding and stratification. The layers thicken and thin, enter 

 and disappear, in a very remarkable way, and that within the space of a few feet. At 

 the same time they curve and dip in various degrees and directions. The accompany- 

 ing cuts, from sketches made on the spot, will serve to show this imperfectly. 



Fig. 30. 



Sketches from Section 15, Nepeubkin. 

 Showing irregular structure of Lower MagneRian limesioue. 



The irregularity is such that it seems necessary to attribute it to the conditions of de- 

 position and not to subsequent disturbance. During the process of deposition there ap- 

 pears to have been more or less of loosening, breaking up, i-ounding and rearranging of 

 the somewhat indurated sediment and its redeposit, intermixed with finer material, but 

 after the final deposition there is no evidence of subsequent disturbance beyond that 

 common to all formations. Northwest of Winneconne these mounds become so pre- 

 valent that the surface of the formation may very fittingly be termed billowy. They 

 seldom exhibit a greater length than forty rods, nor an elevation of more than thh-ty or 

 forty feet, and are usually much less than this. Of course mention is here made only of 

 that portion which protrudes above the drift, and not of the actual dimensions. Their 

 greatest length here, as elsewhere, is east and west. The dip in aU cases, so far tis 



