280 



GEOLOGY OF EASTERN WISCONSIN. 



such a modification of the limestone in its vicinity. But the fact of changeableness ia 

 nevertlieless a general one. 



Tlarough Hortonia the course of the ledge is eastward, in which direction the forma- 

 tion slowly dips, until in the town of Ellington it is covered by the St. Peters sand- 

 stone and Trenton limestone, which, standing out in a similar escarpment, seem to 

 form a continuation of the Lower Magnesian ledge. 



It has already been remarked that the course of the streams in this vicinity is peculiar. 

 The Wolf river, when it arrives opposite tliis rock barrier, turns sharply to the west, 

 while a little stream traiverses the township of Ellmgton in an almost direct line parallel 

 to tliis ledge, and enters the Wolf river at the point of its sudden flexure, This little 

 stream Uea in the level bottom of a valley averaging about a mile in breadth. On its 

 south side, in sections 25 and 26 of the town of EUington, highly fossiliferous limestone 

 of the Trenton period reaches from near the flood plane of the valley upwards, 35 feet or 

 more. On the opposite side of the valley, in section 24, there arises from the same flood 

 plane, a mural cliff of Lower Magnesian limestone to the height of more than 50 feet. 

 The accompanying figure presents the relations of these formations: 



Fig. 34. 



1. Potsdam sandenone. 



3. Lower Maj^eeian limestone. 3. St. Petera sandstone. 

 4. Trenton limestone. 



The rock forming this Lower Magnesian cHff is a very hard, silicious dolomite, of 

 almost flinty texture, striking fire readily from impact of the hammer, and yielding a 

 resonance and fracture more like quartzite than ordinary Umestone. Its distant bedding 

 joints aj:e very obscure, in the main body of the cliff, while irregular vertical fissures are 

 numerous and conspicuous. Geodes of limpid and opalescent quartz are scattered through 

 it. These characteristics pertain in full only to the cliff in question. To the east a low- 

 er ledge of the more usual coarse, siHcioua limestone extends some distance into the next 

 township, and a similar ledge on the west, curves to the north, and is lost under the 

 drift. But it soon reappears and extends with insigrdficant interruptions onward to the 

 vicinity of the Wolf river. Tlie strata, Kke those on the south side of the valley, rise in 

 that direction, so that near the river the upper face of the Potsdam sandstone is brought 

 considerably above the flood plane, and a profile section across the valley at Stephens- 

 viUe would show a very unequal elevation in the Lower Magnesian strata. 



Stai further to the westward, within about two miles of New London, two conspicu- 

 ous mounds, known as North and South Musquito Hill, rise about 200 feet above the R. 

 R. grade at the depot. Their main mass is sandstone, but they are crowned with calca- 

 reous strata. On the western brow of the south hill the uppermost layers exposed are 

 thin, banded, arenaceous and oolitic, and are succeeded below by two feet of shelly, rot- 

 ten, mottled layers, underlaid by sixteen inches of thin-bedded, flag-like rock, under 

 which again hes a foot of hard, broken, chippy rock, which in turn rests upon quartzose 

 sandstone beds of 6 inches to 24 inches in thickness. The actual exposure of the sand- 

 stone is confined to a few feet, but the precipitous slope indicates its presence in conside- 



