Review of Owen’s Geological Report on Wisconsin, Iowa, etc. 93 
the surface soil to such an extent, that a long succession, even of 
exhausting crops, will not materially impoverish the land. he 
prairie-sod, matted and deep-rooted, usually requires from six to eight 
yoke of oxen effectually to break it up. 
The future farms of Iowa, large, level, and unbroken by stump or 
other obstruction, will afford an excellent field for the introduction of 
mowing and reaping machines, and other improved implements calcul- 
ated to save the labour of the husbandman ; and which, in new co 
tries reclaimed from the forest, can scarcely be employed until the 
first generation shall have passed away.—pp. 100, 101. 
The immediate basin of Lake Superior is formed of red sand- 
stones and argillaceous beds, conglomerates and shales overlaid 
and concealed to a great extent by superficial deposits of red 
' clay, marls and drift ; and intersected especially on the northwest 
shore by a multitude of igneous outbursts which have modified 
altered and indurated the adjacent strata, and tilted them locally 
in different directions from the prevalent gentle southeasterly 
he mechanical action and metamorphism which have re- 
sulted, have produced the amygdaloids and conglomerates which 
usually intervene between the red sandstones and dykes of trap. 
' The detailed descriptions of these interesting formations are 
given chiefly in the reports of Dr. J. G. Norwood, and those of 
Col. Whittlesey ; the field of operation of the former gentleman 
having been principally in middle, northern, and northeastern 
Minnesota, that of the latter, along the southern watershed of 
ake Superior, situated between the Michigan line and the 
Bois Brulé River. 
The 4th chapter contains some additional details regarding the 
Other portions of the interior of Wisconsin, Minnesota and the 
valley of Red River of the north, for which we must refer our 
readers to the work itself. 
The crystalline rocks and metamorphic schists first appear on 
the surface about lat. 44° 20’, and occupy, under the superficial 
eposits, a considerable area in the northern and eastern portion 
of the district, both N. W. and S. E. of Lake Superior; but the 
actual surface exposures are limited, inasmuch as the drift de- 
posits have filled up most of the inequalities of the surface, and 
thus conceal to a great extent the hypogene rocks and crystalline 
schists, and, at the same time produce a uniformity and levelness 
of surface which would hardly be anticipated on approaching the 
sources of such important streams as the tributaries that give orl- 
gin to the mighty Mississippi. Even the igneous rocks, forming 
the summit levels, 500 to 1000 feet high, dividing the waters 
flowing into Lake Superior, and those running into the Missis- 
sippi, are, for the greater part of their range, buried beneath heavy 
drift deposits. The country around the sources of the Wisconsin, 
Chippewa, St. Croix, St. Louis and Mississippi are described as 
of this character. Wi 
