NIAGARA LIMESTONE. 3^3 



■ the bedding joints become entirely lost, and, in an exposure of 20 feet, none are visible 

 Vertical seams occur at intervals, which ai-e disposed to change to an angle of 45° with 

 the horizon, and to pass obliquely across to the neighboring fissure. 



If we pass on eastward about half a mile, we find a rock, at a somewhat higher ele- 

 vation, of a more earthy structure, belonging to the Guelph horizon, but when we reach 

 the Milwaukee river, below the rapids, we again find the granular rock, as before, but 

 distinctly bedded and dipping northwai-d. In a few rods, the layers become harder and 

 are almost as soon lost in a brecciated, unsti-atified mass, whose superior hardness has 

 given rise to the rapids. This mass is made up of fi-agments of rock cemented by com- 

 mmuted debris of a dolomitic character, which renders the distinction of the fragments 

 fi-'om the matrix often obscure. Tliis breccia graduates almost imperceptibly into hard, 

 compact layers, as we proceed up tlie river, and these in turn soon give place to granular 

 rocks again, the strata dipping northward for a distance, and then rising, as illustrated 

 in the accompanying figure. 



Fig. 44. 



S>">ji??/-^':^-'X'^.^^!f^T-^^^^^ 



Profile Section along the Milwaokee River, below Grafton, showing the Changeable 

 Nature of the Racine Limestone. 

 a. Soft anil granular; 6. Close-grained and hard ; c. Brecciated ;</. Hard and compact ; d. Granular. 



At the dam near the south line of the S. E. qr., Sec. 24, Grafton, the granular dolom- 

 ite is developed in its most characteristic form, becoming a weU marked calcareous sand- 

 rock. 



Above the dam, a harder rock of closer but irregular texture ensues, but at a some- 

 what higher level, and belongs to the Guelph horizon. 



Near the center of the east Hne of Sec. 33, Cedarburg, there is an outlier of rough, coarse 

 brecciated dolomite of Ught gray color. It is composed of fragments of compact rock, 

 the spaces between which are filled with a yellow pulverulent material. As the ruck of 

 tlie vicinity has been swept away, leaving it about 30 feet higher than its base, it is prob- 

 able that it was surrounded by the softer granular beds that are prevalent in this neigh- 

 borhood. 



Throughout. Ozaukee and Washington counties, this formation is chiefly represented 

 by rocks similar to those already described, but to this remark there are conspicuous ex- 

 ceptions. 



Near the south line of the S. W. }4 oi Sec. 35, Germantown, there is a quarry of 

 considerable lateral extent, though it exposes but about 8 feet vertically. In the western 

 portion of the quany, the upper 13 inches consist of a. hard, close-textured rock, but 

 full of rough, irregular cavities. Below this, and not definitely separated from it, are 

 23 inches of porous, granular rock of the Racine type, showing, on the weathered edge, 

 oblique and cross lamination, (e of Eig. 45.) Below this, are 5 feet of bluish white, 

 very fine grained, compact dolomite, in beds averaging 6 inches in tliiokness. (/ of 

 Fig.) The distinction between this and the rock above is sharp and clear, so that it 

 may be accurately traced, even where the bedding joint does not correspond to the junc- 

 tion. Traced to the northeast, the porous layer of the Racine type is reduced to 18 

 inches within 25 paces. It has also lost much of its porous character, havmg changed 

 so as to be less different from the upper portion, and being now broken up into irregular 

 layers. Five paces farther, this layer is reduced to six inches, and has still farther 

 changed in character, (g.') Ten paces farther, it is no longer recognizable, both it and 



