LOWER MAGNESIAN LIMESTONE. 277 



fact it has a value as a guide in fixing the position of the subordinate divisions of the 

 formation. 



In speaking of the sandstone below, mention has already been made of several locali- 

 ties in Green Lake county, where the lower strata of this formation are visible chiefly in 

 the position of protecting caps covering sandstone hills. 



Mt. Tom, in the township St. Marie, while affording another example of this, exposes 

 a considerable group of the bottom layers of the Lower Magnesian limestone as follows, 

 in descending order: 



1. Rough, silicious, congloineritic dolomite, of dirty gray aspect, weathering to a very 

 ragged surface, which develops prominently its conglomeritic character, and also the 

 many aggregations of white quartz crystals that abound in it; rather thick bedded. 

 Entire thickness of original stratum not known, as it fonns the apex of the hill. 28 feet. 



2. Light bluish gray, thin bedded dolomite of even, fine grained texture, and easy, 

 regular, earthy fracture, which would render it very excellent for building purposes if 

 the courses were thicker, as they probably would be found to be where less affected by 

 surface agencies. 4 feet. 



3. A thick, rough, brecciated bed similar to No. 1 above. 2 feet. 



4. Shelly, magnesian limestone and calcareous shale. The layers are thickest and 

 most calcareous at the top, becoming thinner and graduating into the more shaly por- 

 tion below, which is grayish buff and purple, and appears to be quite arenaceous, though 

 not so in fact. 8 feet. 



5. Coarse, rough, thick bedded, dirty gray, hard, granular, silicious dolomite, contain- 

 ing small inconspicuous geodes; irregularly cracked and fissured, and frequently form- 

 ing over-hanging ledges from the removal of the softer sandstone below. 15 feet. 



. On the slope below the limestone occasional slight exposures of red and yellow Pots- 

 dam sandstone are visible. 



In sections 11 and 14 of Brooklyn, in this county, the beds exposed are unusually 

 geodiferous. Nearly or quite half the volume of the rock in some cases is formed of 

 cavities lined with quartz crystals. These are chiefly red, brown and pink, sometimes 

 forming very handsome, though small and irregular geodes. At numerous other points 

 in Green Lake county, there are slight outcrops of this formation, which do not merit 

 special description, but which may be readily identified by the characteristics already 

 given, or by reference to the accompanying maps. 



In the town of Poygan, Winnebago county, the western limit of this formation is 

 marked by a line of bluffs, along the face of which occasional outbreaks of the strata 

 occur, but no conspicuous escarpments. 



In the N. W. qr. of Sec. 26, a quarry has been opened and a kiln constructed for the 

 purpose of manufacturing hydraulic and quicklime. At the top of the quairy, three feet 

 of thin-bedded undulatory layers of magnesian limestone are burned for the latter pur- 

 pose. Below this is a layer exhibiting very unequal deposition, whose irregularities seem 

 to give rise to the wave-like nature of the beds above. This is underlaid by sixteen feet 

 of a rather soft, granular, argillaceous, magnesian limestone of a slightly olivaceous 

 gray color, which disintegrates readily when acted on by the elements. The beds are 

 below medium thickness, and, in some cases, furnish good flagging, and the material 

 from which the waterlime is prepared, At the base is one foot of a yellowish-gray rock, 

 eight inches of decomposed rotten stone, reposing on the common hard dolomite of the 

 formation, which is very slightly uncovered. 



In the erosion of the Wolf river valley, in Caledonia, Mukwa and Hortonia, the 

 sandstone below was readily removed and the more resisting ledges of dolomite left pro- 

 jecting in vertical cliffs of moderate height. By combining the facts exhibited at several 

 points along this line of ledges, chiefly those in Hortonia, the following section, rep- 

 resenting about 60 feet of the base of the formation, was obtained. 



