20 
STATE AGRICULTURAL SOCIETY. 
Superior, and showing itself on the St. Croix River, which con¬ 
stitutes the upper western boundary of the State, the entire 
northern portion is occupied by rocks of the older formations 
— usually known as Azoic, on account of the absence of the 
remains of animals. They belong to rocks of the granitic, 
sienitic, gneissoid and hornblende class, and owing to their fre¬ 
quent occurrence in large masses, have the appearance of being 
unstratified like the rocks of igneous origin, which have been 
forced up through them, here and there, by some fierce action 
of the great central fires of the earth. They are found, how¬ 
ever, on closer inspection, to have distinct lines of bedding, 
and at some time in the remote past were undoubtedly simple 
sandstone, like the modern rocks of that description. The 
extent and boundaries of this geological district are indicated 
upon the accompanying map of the State by the long oblique 
markings. These rocks are not discoverable throughout the entire 
extent of this area, being obscured by immense beds of drift 
for a considerable distance on the southern, side of the range 
before referred to, but their occasional exposure in low eleva¬ 
tions and their general appearance where the drift thins out 
along the western border of the district leave no room to doubt 
its being the underlying rock. The rocks of igneous origin 
referred to are not found to any extent except along the lake 
shore. Beyond the north-eastern boundary of the State the 
trappean formation is more fully developed, and together with 
the sandstone hereinafter described, constitutes the rock of the 
Copper Region. In some places there are exposures of the 
sienitic rock which must eventually be worked for the valuable 
building stone which they are able to furnish. 
Receding southward from the central area of the Azoic rocks, 
which are the lowest formations in the State of which we have 
knowledge, we come next to the 
Sandstone District , which is also next in the order of super¬ 
position. This rock is thought to be equivalent to the sand¬ 
stone formation at Potsdam, New York, and on this account 
has received the name of Potsdam Sandstone. For economical 
purposes, however, it is much less valuable than the New York 
