DODGE COUNTY. 37] 



Trenton limestone.] 



Below this is a compact limestone, not well exposed. It is not dolo- 

 mitic and is good for burning. 



At the saw-mill near the middle of sec. 17, Milton, the road passes 







around an exposure of rock. Here are about ten feet of shaly limestone 

 and blue clay. A fine specimen of Receptaculites lay in the wheel-track of 

 the road, and had been considerably marred. Many other incomplete 

 specimens were found. 



An eighth of a mile below this saw-mill (still in sec. 17, Milton), is 

 an irregular bluff on the south side of the stream. It is concealed by debris, 

 bushes, etc., and not very accessible. The following measurements and 

 observations were obtained with as much accuracy as circumstances would 

 admit. They are taken from above: 



Section on sec. 17, Milton. 



1. Yellowish limestone in thin layers 10 ft. 



2. Compact aluminous layers, 4 to 6 inches 1 ft. 



3. Shale, limestone, and blue clay in alternate layers, usually thin 15 ft. 



Below, passing under the debris and probably occupying the present 

 river bed is a thick stratum of compact limestone, with a depth of upwards 

 of twenty feet. Receptaculites is abundant in the rock. 



As might be anticipated from the structure of the rock, living springs 

 are abundant along these bluffs. One very fine one, the size of one's arm 

 pours out from the rock just above the saw-mill, at a distance of twenty 

 feet above the water of the stream. Here these springs are almost equal 

 in number in bluffs facing north or south, betraying the absence ot dip at 

 this point in either of those directions. 



Other small exposures of Trenton rock were seen in the road in several 

 places within the Trenton area as marked on the accompanying map, as 

 at sections 19 and 30 of Milton township, and in sections 12, 13 and 14 of 

 Mantorville. The lower parts of the exposures at Mantorville and Wasi- 

 oja are, in all probability, Trenton; but as it is impracticable to tell where 

 this rock begins and the rock above ceases, these exposures will be de- 

 scribed under the Galena. The Trenton can also be traced into this county 

 from Olmsted, in sec. 14, Canisteo, and from Goodhue along the north fork 

 of the middle branch of the Zumbro, near the north county line. 



The Galena limestone is found cropping out along the south middle 

 branch of the Zumbro. In descending this stream no rock is found until 



