Tornado at St. Cloudy Minnesota — HalL 155 



current from Wright county east, northeast to the edge of Wis- 

 consin, proved by the presence of the gray or blue till with lime- 

 stone bowlders overlying the red till; the driftless area, extending 

 into the southeast part of the state to include Houston and 

 Winona counties and the eastern portions of Fillmore, Olmsted, 

 Wabasha and Goodhue counties; the surface of this area being 

 residual clay from eroded strata, partially modified by the water of 

 a lake confined there by the ice-sheet confluent farther south; the 

 beaches of the glacial lake Agassiz, held by the retreating ice-sheet 

 in the basin of the Red and Rainy rivers, the outlines of a similar 

 glacial lake which existed earlier in the basin of the Blue Earth 

 and Minnesota rivers, and the former shore of lake Superior, which 

 in like manner was held 500 feet higher than now, having its out- 

 let south westward to the St. Croix and Mississippi rivers; and the 

 thickness of the drift as shown by deep wells, being found to aver- 

 age 100 to 200 feet upon the western two-thirds of the state, where 

 it conceals the older rocks over large districts, including all of the 

 basin of the Red River of the North in Minnesota. 



20. The subsoils: clay and loam in the Red river valley, in 

 the southwest corner of the state, and on the driftless area; sand 

 and gravel covering considerable tracts from Dakota county, Saint 

 Paul and Minneapolis northwestward to the Crow Wing river 

 and the sources of the Mississippi; gray or blue till, occupying the 

 greater part of the state; red till, reaching from lake Superior 

 southwest to Brainerd and south to Saint Paul; and a track bord- 

 ering the international boundary eastward from Rainy and Ver- 

 milion lakes, where only scanty patches of soil are found, the 

 surface being mostly bare rock with many little lakes. 



May 4, 1886. 



AN ACCOUNT OF THE TORNADO WHICH VISITED SAINT (LOri), MIN- 

 NESOTA, APRIL 14, 1886.— C. W. Hall. 



At seven o'clock on the morning of April 11th, last, an area 

 of low barometric pressure was detected by the U. S. Signal 

 officers centerin"' a few miles north of San Francisco, Cal. This 



