LOWER MAGNESIAN LIMESTONE. 271 



Unfortunately, little is positively known to me concernino- their in- 

 terior. The deeper strata observed were of very irregular character, 

 being either brecciated or showing a tendency to a rude concretionary 

 grouping of material into irregular lump-like enlargements of the lay- 

 ers. In a very few instances, supposed to belong to this class, nota- 

 bly an outlier one mile south of the village of Markesan, the whole 

 of the rock exposed is a thoroughly brecciated mass, with obscure or 

 absent bedding lines. This may, perhaps, be the remnant of a larger 

 mass that formed the nucleus over which the sloping strata were de- 

 posited, for the weight of evidence goes to show that this is a phenom- 

 enon of deposition and not of upheaval. 



Fm. 27. 



SBonoN (north of Stllee) Showhtg the Eelatioks of the St. Peters Sandstone and Lower 



MAONERIAN LntESTONB. 



Organic Remains. These are very meager. Fucoidal remains, 

 Salterena(?), an undetermined species of Stromatopora,; Ophileta uni- 

 angulata, two undetermined species of Trilobites, doubtfully referred 

 to the genus Barthyurus, embrace those found in this region. 



Area. It has been remarked that the Potsdam sandstone area 

 forms a rude crescent, the eastern limb of which enters the district 

 under consideration in Green Lake county, and extends thence to the 

 Menomonee river. The Lower Magnesian limestone forms a serrated 

 band or a fringe on the convex edge of this crescent, averaging about 

 seven miles in breadth. It barely enters the district on the western 

 margin of the counties of Jefferson and Dodge, but invades Green 

 Lake county with its full width, and thence passes diagonally on- 

 ward to the northeast, through Winnebago, Outagamie, Shawano, 

 and Oconto counties, as exhibited on the accompanying maps. 



Thickness. Owing to the uneven surface, the thiuknese varies 

 greatly. The observed extremes in this region are 62 feet and l-il 

 feet. Calculations based on dip give very similar results, but it is 

 highly probable that the thickness sometimes exceeds these limits. 



Local Descriptions. The most southerly point at -wliich the Lower Magnesian hme- 

 stone appears within the eastern district, is at Waterloo, in Jeiferson county. Along 

 the stream below the lower bridge, at the village, a low ledge presents its rough, weath- 

 ered face to view. It consists of a coarse, cherty, buff, silicious dolomite, in medium 

 beds of rough, uneven texture, owing in part to irregular cavities and granular porous 



