228 THE GEOLOGY OF MINKESOTA. 



[Alluvial terraces. 



does not seem to be true that the streams are terraced above the level 

 of this terrace. The highest point at which the terraced condition of Root 

 river has been observed is Preston, in Fillmore county, but it must certainly 

 extend several miles farther up that valley. By aneroid measurements, 

 united with levels of the Southern Minnesota railroad, the hight of this 

 terrace at Preston is found to be about 300 feet above the Grand Crossing 

 of the S. M. R. R. near the mouth of Root river, while the same terrace at 

 Hokah, likewise near the mouth of Root river, is only about one hundred 

 feet above the flood plain. It is also probable that the loam terrace, as seen 

 at La Crescent, is the same continued to and coalescent with the Missis- 

 sippi terrace; and there it is ninety feet above the Mississippi flood plain. 

 This would necessitate a fall, of about two hundred feet in the Root river 

 at its highest stage, in a distance of fifty miles in a right line. Root river 

 valley, between the rock bluffs, has an average width, through Houston 

 county, of about two miles. 



There is, besides this high loam-terrace, a second terrace level, visible 

 specially at La Crescent, on the Mississippi, which there rises fifty feet above 

 the flood plain of the river and spreads out in a pleasant plateau on which 

 the village has been located. This terrace is made of gravel and pebbles 

 of northern origin, and was identified only along the Mississippi. The lar- 

 gest stones it contains are about three inches in longest diameter. Tt is 

 passed through in wells, and seems to be entirely pervious to water, as all 

 the wells on it get water at about the level of the flood plain of the river. 

 This material is used for grading and road-bed, on the C. D. & M. R. R. and 

 elsewhere. It consists entirely of rounded water-worn materials, the main 

 part being the usual parti-colored quartzyte pebbles, granitic, hornblendic, 

 amygdaloidal and lamellar, as well as uniform and massive. A great many 

 of them have a red color, or some shade varying from red. The coarsest 

 pieces are rare, found only in the upper portions of the debris of alluvial fans. 



The following more special observations were made on these terraces 

 in Houston county. 



At Sheldon, six miles from Root river, in the valley of Beaver creek, the terrace on which 

 the Newberry House stands is thirty feet above the water of the creek below the dam. The ma- 

 terials of the terrace at this place are sandy loam horizontally stratified, with more clay near the 

 top, and less evident stratification. 



At Houston the only observable terrace, measured about a mile west of the city, is sixty-five 



