286 THE GEOLOGY OF MINNESOTA. 



[Shakopee limestone. 



and its tributaries than any other formation. As it lies between two sand- 

 stones, each of which easily crumbles away under the operation of the 

 elements, it is made to have a prominent position in giving form to valleys 

 and river bluffs. The north branch of Root river enters it about six miles 

 northwest of Chatfield in Olmsted county; the middle branch near the town 

 line between Chatfield and Jordan, and the south branch but a short dis- 

 tance below Forestville. South Root river strikes it near Henry in Amherst 

 township. Thus throughout about two-thirds of the county it is the con- 

 stant companion of the traveler along the river valleys, and it meets him 

 often in the uplands, and in the valleys of little creeks. Its effect on the 

 topography is to render the valleys narrow, rocky and abrupt. East of the 

 general area of the St. Peter sandstone and the Trenton limestone it pro- 

 duce j a shoulder in the descent from the uplands to the valley. The fol- 

 1 ,:\ ing diagram, taken at Chatfield on the northern boundary of the county, 

 illustrates in general the effect of this limestone in producing a terrace 

 along the lower slopes of the river bluffs. 



drift gravel 



FIG, 17. PROFILE OF THE NORTH SIDE OF THE VALLEY AT CHATFIELD. 



Explanation. 



1. Loam ............. .................................... 6 16 feet. 5. St. Peter ........................................................ 1J2 feet. 



2. Upper Trenton ................................... 2050 feet. 6. Shakopcc.. ........................................................ 30 feet. 



S. Green shale ......................................... 15 feet. 7. Flood plain. 



4. Lower Trenton .................................... 20 feet. 



The descent from the general level of the country at Chatfield (No. 1) 

 to the river (No. 7) is about 222 feet, of .which about thirty feet are of the 

 Shakopee, the Shakopee being at the river. The broad terrace on which 

 Chatfield stands is constituted of the Shakopee overlain by irregular thick- 

 nesses of the St. Peter, with some drift and loam. The lithology of the 

 Shakopee is very much the same in Fillmore county as has been described 

 in reports on Houston and Winona counties. It is very similar to the 

 St. Lawrence, with much less of green-sand. It contains at Chatfield con- 



