inland with those of the same deposits on the harbor-islands, (a
series of evidence to be given with more detail in a future article,)
suggest a different explanation of these phenomena. The sheet of drift
was once more continuous and extensive than it is now, and the
localities in which we find these crops of boulders are spots where the
tide has eaten into the drift, wearing away the finer materials, or the
paste in which the larger fragments were imbedded, and allowing them to
fall to the bottom, or where the same result has been produced by the
action of rivers cutting their way through the drift, and thus finding
an outlet to the sea. In short, instead of showing the power of currents
to carry along heavy fragments, these stranded boulders prove, on the
contrary, the inability of water to produce any such effect, since it is
evident that the tides washing against the shore, or the rivers rushing
down to the sea, were equally incapable of bearing off the weightier
materials, and allowed them to drop to the bottom, while they readily
swept away the lighter ones. Such localities compare with the
surrounding drift much as the bottom of a gravel-pit which has been
partially worked compares with its banks. Look into any gravel-pit, a
portion of which has already been carted away. At its bottom a number of
larger stones and boulders are usually lying, too heavy for the cart,
and therefore left upon the spot. Fragments of the same size and
character, and equally numerous, will be seen protruding at various
heights from the sides, where they are imbedded in the general mass of
the drift. As soon as the work progresses a little farther, and the
finer materials are removed, these boulders will also drop out, and lie
as thickly scattered over the surface of the ground, as they now do in
that portion of the bottom where the pit has been completely opened and
the gravel removed. We shall see hereafter how these boulders, derived
from the land-drift and scattered along the coast, may be distinguished
from those cast ashore by icebergs.

Notwithstanding the number of facts thus far collected respecting
glacial phenomena in America, certainly forming in their combination a
very strong chain of evidence, the scientific world has, nevertheless,
been slow to admit the possibility of the former existence of glaciers
over such a wide, unbroken expanse of level land. This backwardness is,
no doubt, partly due to the fact, that, as glacier