The Glenwood beds occupy a position between the St. Peter sandstone and the Platteville limestone of the upper Mississippi Valley. They consist of arenaceous to argillaceous yellowish gray to green shaly beds, or series of beds, which persist in general character and horizon, from Illinois to Minnesota. They were named and originally described by Calvin, in Iowa.1 The thickness of the shaly beds, which constitute the more typical part of the Glenwood, does not, in general, exceed eighteen inches to three feet, but in places three, four, or more feet of the sand below it is mingled with argillaceous material and appears to have been disturbed by the advancing sea in which the shale was deposited. At some places in the vicinity of Fountain, Minnesota, and Oregon, Illinois,2 the argillaceous shale is succeeded by several beds of sandstone; at other places, a thin argillaceous limestone occurs at that horizon. . . .