BLUE EARTH COUNTY. 425 



St. Lawrence limestone.] 



tered in the Mankato well, according to Mr. G. C. Burt, at 290 feet, and 

 extended 163 feet to the depth of 453 feet below the surface. Besides the 

 magnesian limestone from which the formation takes its name, it includes 

 beds of shale and sandstone, mostly calcareous; and in all these deposits 

 it contains green-sand, sometimes in minute scattered grains, but often in 

 considerable amount, forming so large a proportion of the rock as to make 

 it appear like green shale, in the specimens pulverized by drilling. 



The only outcrops of the St. Lawrence limestone in this county are in 

 the valley of the Minnesota river in Judson; and, with the ledges of the 

 same rock on the opposite side of the river, at Hebron, in Nicollet town- 

 ship and county, these are the first exposures of the Lower Magnesian 

 series found in descending this valley. Along all the lower part of the 

 Minnesota river, alternate strata of limestone and sandstone belonging to 

 this series are frequently exposed in the bluff's and bottomland. 



In Judson, at the middle part of the north side of the township, the St. Lawrence limestone 

 is exposed along a distance of about one and a half miles, and has been considerably quarried at 

 several places. It rises 30 to 35 feet above the river, and forms the border of a terrace covered 

 by modified drift of the same hight and a half mile wide, which lies between it and the bluffs. 

 Next southeast, at the east line of section 3, Judson, the road ascends to a terrace 60 feet above 

 the river and a quarter of a mile wide, composed superficially of drift and abundantly strown with 

 granitic and gneissic boulders of all sizes up to ten feet in diameter. Eastward this terrace sinks 

 a little, to a hight about 45 feet above the river, and near the middle of the south part of section 

 2 it shows a bed of reddish arenaceous limestone, which does not, however, rise above the surface 

 of the drift. It is believed to be the upper part of the St. Lawrence formation. Leaving this 

 terrace at about a half mile farther southeast, the road next climbs about 125 feet in the N. W. J 

 of section 12, passing an unnamed waterfall in the Jordan sandstone, the brink of which is about 

 90 or 100 feet above the river. 



At Mrs. G. W . Wolf's house (Judson post-office), in the S. E. J- of section 33, this limestone has 

 been quarried along an extent of about twenty rods, exposing a vertical thickness of four to eight 

 feet, the top being 30 to 35 feet above low water of the river. Another quarry on the same farm, 

 about sixty rods farther southeast, also shows a thickness of eight feet. The section here is at 

 top 5 or 6 feet of a very hard and durable, flesh-colored or buff, magnesian limestone, somewhat 

 striped or mottled with greenish tints, in layers from a few inches to one foot thick, having their 

 planes of bedding and jointage often covered with green films; then a dark greenish, sandy 

 shale, much of it finely laminated, crumbling under the influence of the weather, 1J feet; chang- 

 ing below to a yellowish gray calcareous sandstone, about 4 feet thick; underlain by sandy shale, 

 which is blue for its first foot, becoming yellowish gray below, excavated only 2 or 3 feet, but 

 reaching deeper. 'All these beds, and their other exposures, both in Judson and Nicollet, are 

 nearly level, but appear to have a slight general dip, in some portions amounting to two or three 

 degrees, to the southeast. 



About a third of a mile west of Mrs. Wolf's, a hard calciferous sandrock is exposed along a 

 little creek for a distance of a quarter of a mile, sometimes showing a vertical thickness of six feet. 

 It is green when first uncovered, but weathers to a mottled buff, of yellowish and reddish colors. 

 It is probably the same with the third stratum of the foregoing section, and with the arenaceous 

 limestone and crumbling sandstone seen in the race-way of the stone mill at Hebron. 



Near the ferry, about a mile east from the first described outcrops, a thickness of eight feet 

 of this limestone is seen at John Goodwin's qnarry, lying 25 feet above the river. Professor 



