568 THE GEOLOGY OF MINNESOTA. 



[Trees and shrubs. Geological structure. 



The lakes of Redwood county and of western Brown county have only narrow margins of 

 timber; but in central and eastern Brown county groves of considerable extent border Sleepy 

 Eye lake, the southeast part of lake Ilanska, and lakes Armstrong and Linden, and reach a mile 

 southeast from the last, to Emerson lake. 



At Sleepy Eye lake the principal species of trees are bur oak, bass, white and red or slippery 

 elm, white ash, box-elder, cottonwood, poplar, hackberry, the Kentucky coffee-tree and the wild 

 plum. Wood here is worth from $2.50 to $5 per cord, according to quality. 



in northwestern Redwood county, Mr. Malcolm McNiven enumerates the following species 

 of trees and shrubs occurring at Swan lake, on the west line of Underwood: white elm, white 

 ash, box- elder, cottonwood, wild plum, willows, Virginia creeper, climbing -bitter-sweet, frost 

 grape, prickly ash, choke-cherry, black currant, and prickly and smooth wild gooseberries, 

 common; and bur oak, hackberry, poplar or aspen, wolf berry, black and red raspberries, thorn, 

 and wild rose, less frequent. Species not found at Swan lake, but common or frequent on the 

 Redwood river, are bass, red or slippery elm, iron- wood and sugar maple. Red cedars grow on the 

 cliffs of this river at Redwood Falls, and from them appears to have come the name of this river 

 and thence of the county. 



The Cottonwood river is said to have its name, which also has been given to a county, from 

 a very large, lone cottonwood beside this stream in the south part of Redwood county, about 

 seven miles northwest of Lamberton; but this tree has also a luxuriant growth throughout the 

 timbered bottomlands of this river. 



The northern limit of the black walnut appears to be at the walnut grove, of about a hun- 

 dred acres, from which comes the name of the neighboring station and village on the railroad, the 

 grove itself being on Plum creek in sections 25 and 36, Springdale, close to the south line of 

 Redwood county, and one to two miles southwest from Walnut Grove village. 



GEOLOGICAL STRUCTURE. 



The foundation of Brown and Redwood counties, northwest from New 

 Ulm, consists of metamorphic gneiss and granite, belonging to the great 

 series denominated Eozoic or Archaean, which embraces the most ancient 

 rocks known to geology. This is overlain by various shales, sandstones, 

 limestones and clays, the latter sometimes holding beds of lignite, which 

 are regarded together as of Cretaceous age. Exposures of these Creta- 

 ceous rocks continue in the Minnesota valley southeast from New Ulm, 

 but there and through southern Brown county they probably lie upon red 

 Potsdam quartzyte, which outcrops on each side. Upon the east this 

 quartzyte is seen in Courtland, N icollet county, two miles southeast from 

 New Ulm. It is not exposed in this part of Brown county. Upon the 

 west it makes a massive ridge, as described in the report of Cottonwood 

 county. The north base of this ridge reaches into Stately, making falls 

 in section 31 on one of the head-streams of Mound creek. Cretaceous 

 strata, including lignite, outcrop in the bluffs of the Redwood river close 

 north of Redwood Falls; in the southwest bluff of the Minnesota river a 

 few miles farther east, near Crow creek; in the bluffs of Fort creek near 

 Fort Ridgely, in the west extremity of Nicollet county and close to the 



