682 FF, W. SARDESON 
dence indicates strongly that they were not. For example, a 
large pit opened by the Austin Brick and Tile Works showed 
about ten feet of clay of all colors jammed together, bearing 
bowlders of granite, especially in the upper part, and large blocks 
of Devonian limestone, especially in the lower part. There is 
no mistaking the blocks of limestone, for they pass gradually 
into that which underlies in heavy strata throughout this region. 
The limestone blocks are blue or buff like the Devonian strata 
in color, though, locally, they are found in every degree of 
decomposition, so that in one place a complete series from fresh 
rock to iron concretion and red clay can be gathered. At Varco, 
below Austin, in quarries of the Austin Cement Works, a pre- 
glacial channel about ten feet deep in the Devonian limestone is 
well shown, and in it the rock surface is black stained and 
decomposed. Upon this surface is a somewhat disturbed, varie- 
gated clay, not in strata but coating the inclined surface. Recon- 
structed, the preglacial condition around Austin seems to have 
been simply that the Devonian limestone, blue in original color, 
passed upwards into buff of the same formation. This, twenty 
feet or more thick, was penetrated by clay-filied cracks at the top, 
or covered by a coating of black iron-manganese oxide, etc., from 
one to two inches thick; the former condition passing to a red 
clay with black concretions and decomposing brownish lime- 
stone blocks ; the other phase, that of the black unbroken rock 
surface, as at Varco, passing simply into homogeneous residuary 
clay. The pea-green clay is calcareous and it was not residuary 
but formed strata or lamine between the limestones. Sucha clay 
is seen in the Devonian at Le Roy, in the scutheastern part of 
the county,” and again it should not be forgotten that the Devo- 
nian at Austin extends upwards nearly to the horizon of the 
Rockford shales, so well developed southward in Iowa. 
The identification of the clays at Austin as Cretaceous was 
based upon a few specimens of fossil leaves found in digging a 
well (wide op. cit. p. 354). At first the subjacent limestone was 
also called Cretaceous by N. H. Winchell, but this mistake was 
™See also Geol. Surv. Minn., Vol. I, p. 357, 1. 7. 
