NIAGARA LIMESTONE. 343 



complete the exposure. The two chipstone layers are worthy of note, as they may be 

 recognized more than a hundred miles to the northward. 



In Delafield, the next town north, notwithstanding the drift, the formation discovers 

 itself at several points, though nowhere in great force. Its character is essentially as in 

 Ottawa. At the quarry near the village, the two shaly layers are observable. 



At Audley and Graham's quarry (S. E. qr., Sec. 20), a few layers of dark, gray 

 crystalline limestone, containing much chert, are burned for lime. The analysis of this 

 has already been given. At Roberts' quarry, south of Pewaukee Lake (S. W. qr. of S. 

 W. qr., Sec. 24, Delafield), the beds are more close-textured and silicious than at the 

 points previously described, and the chert is more distinctly arranged in layers along 

 the bedding joints. The exterior of the layers is buff, while the interior is blue, the lat- 

 ter sometimes appearing as a well-defined rectangle, surrounded by a border of buff', 

 when a block has been broken across. The whole was undoubtedly once blue, and the 

 buff has been caused by leaching, and the peroxidation of the iron present. 



The formation again disappears beneath the drift, and is next seen in the town of 

 Ashippun, in Dodge county, where it forms a few ragged outlying ledges. The most 

 noteworthy of these lies in the west half of Sees. 6 and 7. It rises about fifty feet above 

 " the grade," at its base, though the vertical ledge only presents a face of about twenty 

 feet. 



The bedding joints are very obscure, and the layers are traced with difficulty, so that 

 the rock presents a very massive appearance, but a general section, somewhat as follows, 

 may be made out. Six feet exposed at the base consist of a hard, but porous, dolomite 

 of uneven texture, made up of fine and coarse grained patches, mottled gray and buff 

 correspondingly. This is overlaid by from 4 to 6 feet of very hard, compact, flintliko 

 limestone, much fissured vertically. Upon this rest 7 to 8 feet of a reddish buff, gran- 

 ular, somewhat friable, magnesian limestone, the granules consisting of small crystals 

 of dolomite, the spaces between which are mostly unfilled, giving a porous structure. 

 Chemically, this is a very pure dolomite, and should be burned for lime instead of either 

 of the other layers exposed at this point, as it would not only produce a superior quality 

 of lime, but would burn easier. This is undoubtedly the equivalent of the " sandstone " 

 layer near Taycheedah, and is the most valuable portion of the beds under consideration. 

 This is overlaid by 6 feet or more of brecciated rock, consisting of subangular fragments 

 of a gray magnesian limestone, imbedded in a yellow, granular matrix of similar chem- 

 ical nature. 



North of this, the margin of the main body of the formation recedes to the eastward 

 as far as Hartford. Near this place are several limited exposures of these beds, one of 

 which, on the farm of Mr. Blodgett, is interesting on account of the fossils it contains, 

 a list of which has already been given. The rock is a light colored, granular dolomite 

 of irregular texture. 



Passing by several outcrops in Herman, we find at Iron Ridge, reposing on the ore- 

 beds, 6 feet 8 inches of buff magnesian limestone, in beds of 8 to 16 inches thickness. 

 Upon this, lies a layer 6 feet 8 inches thick, the bedding planes of which are very obscure, 

 so that it appears like a single layer, while vertical fissures are frequent. This is over- 

 laid by 2 feet 10 inches of thin bedded magnesian limestone, which gives place above to 

 a shaly layer, composed of rotten chipstone, mingled with a greenish blue clay. The 

 whole is capped by about 6 feet of broken, frost-riven limestone. As the mining pro- 

 gresses backward from the face of the ledge, the thinner beds will doubtless be found 

 uniting into thicker and more solid ones, and the disintegrated rock will give place to 

 that which is more firm, with corresponding changes in color and general aspect. 



From this point northward, there is no dearth of outcrops. The Kettle Range has 

 receded to the eastward, and there is left only the usual drift deposit, through which 

 the formation boldly thrusts its jagged edge. 



