546 GEOLOGY OF CENTRAL WISCONSIN. 



and in one or two places in the town of Westport, Dane county, 

 and probably exists in considerable quantity in the country about 

 Lake Mendota. The peculiar phase which yields the Madison build- 

 ing stone is, however, local, and quite inconstant. More commonly 

 the formation is made up of white and brown friable sandstone, nearly 

 or altogether without calcareous admixture. The brown layers are 

 occasionally quite ferruginous and firm, yielding a fair quarry stone. 

 The white sandstone is frequently a loose, white, purely silicious sand, 

 and would be of considerable value for glass making. In one place 

 on the western side of the town of Honey Creek, the Madison sand- 

 stone has a very unusual character, containing layers of a much indu- 

 rated, fine-grained, smooth-faced, pink-tinted rock of very pleasing 

 appearance. 



The Mendota limestone is more frequently quarried than the Mad- 

 ison sandstone. It is not anywhere burnt into lime, being usually 

 too impure, and always too dark colored, but the heavy yellow layers 

 that characterize some ten to 15 feet of its middle portions, are to be 

 seen in scores of quarries, most numerously along the Wisconsin 

 valley. These layers yield a very regular stone, of any thickness 

 from a few inches to two or three feet, which is commonly used for 

 flagging or foundations, but occasionally for constructing entire build- 

 ings. The mill at Cambria, Columbia county, is built of rock from 

 the Mendota horizon. 



The Potsdam sandstone itself is generally altogether too friable to 

 be used as a building material. At numbers of points in the Baraboo 

 valley, however, a firm, fine-grained, white rock is obtained in large 

 blocks. A similar rock is quarried on several of the isolated bluffs 

 in Juneau, Adams and Jackson counties, the horizon being about 200 

 to 300 feet below the summit of the series. A very much indurated, 

 frequently quite coarse, rock is obtained at a still lower horizon at 

 Packwaukee, Marquette county, near Wautoma, Waushara county, at 

 Stevens Point, Portage county, near Grand Rapids, "Wood county, and 

 at Black River Falls, Jackson county. This rock is very regular in 

 bedding, white to straw colored, and makes a very durable and sightly 

 building stone. 



Limonite iron ores, of good quality, and in sufficient quantity to 

 run two small blast-furnaces, occur in connection with the Lower 

 sandstone in Sauk and liichland counties, just west of the limit of 

 the Central Wisconsin district. Within that district, the only ore ob- 

 served in any promising quantity occurs in the upper layers of the 

 high-level sandstone that flanks the quartzite range in the eastern 

 part of the town of Westfield, Sauk county. Here, at a number of 



