When we consider the physical aspects of the countries where the question was studied, we cannot much wonder that the truth was so hard to find. In the midst of corn-fields and meadows, one cannot readily realize the fact that the spot where they stand has been the site of a wide-spread sea; and that where now villages and green lanes meet the eye, there once swam the porpoise and the whale, or monsters of a still earlier creation, unwieldy in bulk and uncouth in form. Such changes, however, must have been, for their traces meet us on every hand. We have the sea dashing against our shores, and there seems nothing at all improbable in the assertion that once it dashed against our hill-tops. No one, therefore, has any difficulty in giving such statements his implicit belief. But who could have dreamed that these fields, so warm and sunny, were once sealed in ice, and sunk beneath a sea that was cumbered with many a wandering iceberg? Who could have imagined, that down these glens, now carpeted with heath and harebell, the glacier worked its slow way amid the stillness of perpetual snow? And yet strange as it may seem, such is the true solution of the problem. The boulder-clay was formed during the slow submergence of our country beneath an icy sea, and the rock-surfaces owe their polished and striated appearance to the grating across them of sand and stones frozen into the bottom of vast icebergs, that drifted drearily from the north. That we may the better see how these results have been effected, let us glance for a little at the phenomena observable in northern latitudes at the present day. Icebergs are formed in three principal ways:--1st, By glaciers descending to the shore, and being borne seawards by land-winds; 2d, By river-ice packed during spring, when the upper reaches of the rivers begin to thaw; 3d, By coast-ice.