PLATE XXXVIII. 



RENVILLE COUNTY, 1888. WARREN UPHAM. 



The surface features of western Sibley and McLeod counties are extended west- 

 ward over this county. There are no rock outcrops except in the valley of the Min- 

 nesota river and near the mouths of Beaver and Birch Cooley creeks. The county, 

 therefore, presents a monotonous expanse of prairie, whose undulations are broad 

 and slight. The greatest variety of surface is found in Hector, Melville, Osceola and 

 the west part of Brookfield. In section 5, Hector, are some kame-like hillocks of 

 sand and gravel, which rise about forty fe^t above the depression along the north 

 side. The bluffs of the Minnesota valley are from 175 to 200 feet high, and the 

 valley is from one to two miles wide. Within it are numerous rough tracts of granitic 

 rock which sometimes rise to 100 or 125 feet above the river itself. These granitic 

 or gneissic outcrops are continuous on the north side of the river for about sixteen 

 miles, viz., from Birch Cooley to the east line of Sacred Heart, and there are isolated 

 granitic areas further northwest as well as southeast. Below Birch Cooley creek 

 similar rocky knobs are abundant on the south side of the river, in the town of Sher- 

 man, Redwood county. 



The crystalline rocks of this county are very largely composed of granite or 

 massive gneiss, and they are apparently in the southwestward line of strike of similar 

 rocks from Stearns and Morrison counties. At Morton these rocks have been exten- 

 sively quarried. They afford there a beautifully banded gneiss. It is there cut by 

 large dikes of diabase and it includes isolated masses of dark schist. 



The most interesting aspect of the crystalline rocks is seen in the kaolinic product 

 of their decay. This product is sometimes from ten to twenty feet thick. It is abun- 

 dant at Birch Cooley and in the west part of section 21, Beaver Falls, along the road 

 descending to the Redwood Falls ferry. It has been mentioned in connection with Red- 

 wood county. This kaolinic substance extends widely under several counties, and it 

 contributed to the bottom beds of the Cretaceous which, in some cases, have been found 

 to consist of a white, fine kaolin, evidently the result of gentle washing and transpor- 

 tation of the original decayed granite. It is in this assorted and washed condition that 

 this clay is likely to be found of economical value for the making of pottery and 



china ware- 



So far as known the Cretaceous has but a scant representation in Renville county, 

 but it is very probably present under the drift in most of the county, since it exists in 

 Redwood county, next south, and in Stearns county, toward the northeast. 



In the drift in the central part of Renville county are found traces of an inter- 

 glacial soil and forest similar to the phenomena in McLeod county. This vegetable 

 debris lies on quicksand, underneath thirty or forty feet of till, N. H. w. 



