570 GEOLOGY OF CENTRAL -WISCONSIN. 



but has been reached by a small shaft sunk on tiie summit of the Uuff. The shaft pen- 

 etrates: J) sandrook, lower layers thin, white and shaly, 25 feet; (2) green and red shale 

 "" 2)2 feet, and ends in (3) sandrook again, the same as that seen on the cliffs. The green 

 .shale appears to be of the same kind as that laiown at several horizons, in the Lower 

 Sandstone in other parts of the state, but is soft and clayey, unusually free from siii- 

 cious sand, and of a deep green color.' The red shale (1342) is soft, slightly sandy, non- 

 calcareous and of a briok-red color. This shaly layer has influenced the denudation of 

 other bluiTs seen to the southeast, which have their summits at the same elevation as 

 this bench. It appears probable that the Camp Douglas bluffs may owe then: con- 

 stancy of elevation to the same cause. All the sandstone on the cUffs of th6 Mauston 

 bluff is non-calcareous, generally moderately coarse, brownish, pinkish and light-colored 

 in different layers, and much of it firm enough to use in onilding. It is quarried near 

 the south end ot the bluff, at the base of the chfi', where firm, heavy layers are ob- 

 tained of a Hght-colored, medium-grained rock (1847); and also at the summit of the 

 cHff, near the north end of the bluff'. At the latter place, immediately above the quarry 

 beds, and just beneath the green shale, are a few layers of a porous, very friable brown- 

 ish sandstone, with numerous u-on-stained points and cavities and indistinct fossil im- 

 pressions, which consists of subangular grains of glassy quartz. On the cliff' below the 

 quarry the sandstone is penetrated by numerous brownish veins, one-sixteenth to one- 

 half an inch in width, which, oh close examination, are seen to be made up of the 

 grains of the sandrock, more glassy than usual, and closely cemented by a small amount 

 of hydrous iron oxide. 



In the southern part o£ the town of Lyndon, on Sec. 28, T. 14, R. 5 E., a narrow, 

 ridgy crest rises 200 feet above the general level of the watershed, reaching an altitude 

 of nearly 700 feet above Lake Michigan. At the summit a white, oherty material (1380) 

 resembling that described as occurring on Sec. 12, town of Wonewoc, remains in place. 

 It is peculiar in showing numerous little rounded holes, that give to the mass some ap- 

 pearance of an organic structure. Ten feet below the chert, fine-grained, non-calcareous, 

 whitish sandstone (1332) is exposed, made up of grains of very fine, sharply angular, 

 glassy, quartz, and resembling that seen below the chert on Sees. 12 and 1, town of 

 Wonewoo. The horizon is evidently the same, and is just beneath the base of the Lower 

 Magnesian limestone. 



The gorge known as the Dalles of the Wisconsin has been briefly described on a 

 previous page. Along the walls of the gorge, which are from 50 to 100 feet in height, 

 the rock is quite uniform in character, being coarse, very friable, light to dark brown in 

 color, non calcareous, and consisting of very much rolled grains of quartz (1443). The 

 most remarkable feature of these exposures, which are nearly continuous for as much as 

 seven miles, is the cross lamination which affects layers as much as 12 feet thick, and is 

 abruptly termuiated above and below by horizontally bedded layers. The transverse 

 laminaB themselves are quite thin, and easily separable from one another. They are not 

 plane, but constitute much warped surfaces. The structure is quite well shown in the 

 view represented on Plate lA, which is taken from one of Mr. H. H. Bonnet's excellent 

 photographs. Plate I, also from one of Mr. Bennet's photographs, shows a peculiar 

 erosion form, known as Stand Rock, which occurs well up on the north face of the high 

 ground through which the Dalles are out, and far above the gorge itself. It illustrates 

 weU the way m which much of the lower part of the Potsdam series is worn— thin layers, 

 somewhat more ferruginous and firm than the rest, though still quite friable, protecting 

 the softer, scarcely coherent rock below. Half a imle east of the upper end of the 

 DaUes, on the east side of the S. E. qr. of See. 21, T. 14. R. 6 E., the " Elephant's 



' Thi8 groeu Rhale has been the object of exploitation as a copper ore, a consideralile amount of 

 money liaving been expended m sinliing shafts, etc. It is hardly necessary to say that the money 

 !s thrown away. 



