THE STATE OF MAINE. 23
range of mountains, several miles north. There are doubtless larger
bowlders than this in Maine.
Another remarkable effect of the drift action is seen in the smooth-
ing, rounding, scratching and furrowing of the ledges. In Maine,
almost invariably, the rocks on the north side of the eminences are
smoothed and grooved, while the south side is without either. Often,
indeed, both sides are covered with drift material and deposits, so that
the rocks are hidden.
There have been alternate depressions and elevations of onr whole
territory in the past ages. The first which we can trace was at the
close of the drift period, when there was a sinking of the land below
its present level,—when the waters sifted out the finer materials of
the drift, and formed beds of clay and stratified sand. Again, there
was a sinking of the land to a greater depth; and, it is quite likely, to
a greater depth in some regions than others. Marine shells have been
found in the clays all over the State, showing that for many centuries
there were depressions of some 25 feet, and then of a 150 ; and perhaps
others to a greater depth.
Then there was an elevation of the land. The river beds, then full
of sand, clay and gravel, were washed out by the dividing flood, as the
land emerged from the sea. These sweeping floods gave place, after
centuries to many a series of lakes, whose waters, cutting their way
through their alluvial barriers, gradually formed tbe rivers that drained
them. These, wearing deeper and deeper into their beds with each
successive season, constantly narrowed their streams as the reservoirs
diminished. Thus the successive beds of the river became terraces on
their shores, forming sandy plains or rich intervals.
There are various minor details of surface geology in Maine not
often observed to which we have not space to allude. Of these, the
most notable and common are the horsebacks, to which allusion was
made in the article on Valleys.
Economic geology must have a little attention. Iron ores in quan-
tities that would yield a profit to the miner are found at several points
in the State. The Katahdin iron works on Pleasant River in Piscata-
quis County, have long produced an excellent metal from an extensive
deposit of bog iron ore found in the vicinity. Dr. Jackson discovered
a fine bed of red hematite iron ore in Waite Plantation, Aroostook
County. Similar beds are found in ITodgdon and Linneus. There is
a bed of bog ore in New Limerick, adjoining the former towns ; also
in other parts of the State, in the towns of Newfield, Shapleigh, Ar-
gyle, Clinton, Williamsburgh, Bluehill, Lebanon, Union, Canton, Paris,
Jewells Island, Thomaston, Bristol, Buckfield, Dixfield, Dover, Farm-
ington, Greenwood, Jay, Rumford and Winslow. Magnetic iron ore
is "found on Marshalls Island and in Buckfield.
Lead ores are found in Lubec (where it is mined) at Kezar Falls,
Parsonsfield, in Denmark, Dexter, Corinna, St. Albans and other
places. In the middle section of the State small boulders of this ore
are rich in silver. Zinc and copper ores are found with the lead at
Lubec, West Quoddy Head, in Cutler, and other towns in the southern
portions of Washington and Hancock Counties, and in Carroll and at
some other points in the eastern part of the Aroostook County.
Tin is found at Bluehill in the ore called wolfram, and the metal
itself at Mount Mica in Paris. Manganese is found in Thomaston,
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