moutonnées. Wherever the natural surface of any hill, having a steep southern slope, is exposed, the marks are always found to be very distinct on the northern side and entirely wanting on the southern one, showing, that, as in the case of many of the roches moutonnées in Switzerland, the mass moved up the northern slope, forcing its way against it, grinding and furrowing the northern face of the hill as it moved over it, but bridging the opposite side in its descent without coming into contact with it.[1] This is true, not only of hills, but of much slighter obstacles which presented themselves in the path of the ice. Even pebbles imbedded in masses of pudding-stone, but rising sometimes above the level of the general surface, often have their northern side polished and scratched, while the southern one remains untouched.
Moraines are not wanting to complete the chain of evidence respecting the ancient existence of glaciers in this country, although we cannot expect to find them here so frequently as in Europe, where the many local glaciers in circumscribed valleys afforded special facilities for the building up of these lateral and transverse walls. Over the broad expanse of the United States, on the contrary, with such slight variations of level, the disappearance of the ice at its breaking-up would naturally be more complete and continuous than in a country intersected by frequent mountain-chains, where the ice would linger in the higher valleys long after it had disappeared from the plains below. Yet it is evident that here also in certain localities the boundary-line of the ice underwent oscillations, pausing here and there long enough to collect mounds of the same character as those spanning the valleys of Switzerland and Great Britain. We have several of these mounds in our immediate vicinity. The Waverley Oaks, so well known to all lovers of fine trees in our community, stand on an ancient moraine, and there are others in the neighborhood of the Blue Hills. In the southeastern parts of Maine, also, I have observed very well-defined moraines. In Vermont, the valley of the Winooski River retains ample traces of the local glacier by which it was formerly filled; and, indeed, throughout the Alleghany range, in its northeastern as well as its southern extension, we have various evidences of localized glaciers, which must have outlived the general ice-period for a longer or shorter time.
I am unwilling to weary my readers by dwelling upon appearances identical with those already described; but I may state, for the guidance of those who wish to investigate these traces for themselves, that any recently uncovered ledge of rock in our neighborhood, the surface of which has not been altered by atmospheric agencies, presents the glacier-worn surfaces with the characteristic striæ and furrows. These marks may be traced everywhere, even to the sea-shore, not only down to the water's edge, but beneath it, where-ever the harder rocks have resisted the action of the tides and retain their original character. In our granitic regions intersected by innumerable trap dikes, as, for instance, at Nahant, the smooth surface of many of the rocks, where sienite and trap have been evenly levelled, shows that the same inexorable saw, cutting alike through hard and soft materials, has passed over them. In the hills of pudding-stone in the neighborhood of Roxbury, we have quartz pebbles cut down to the same level with the softer paste in which they lie imbedded with pebbles of sandstone, clay-slate, gneiss, and limestone. In the limestone regions of Western New York and Northern Ohio, about the neighborhood of Buffalo and Cleveland, the flat surfaces of the limestone are most uniformly polished, furrowed, and scratched, the furrows often exhibiting that staccato grating action described in a former article. I have observed the same traces in the vicinity of Milwaukee and Iowa City, and we know, from the accounts given by Arctic travellers of their overland expeditions, that these peculiar appearances of
- ↑ Fuller descriptions of these polished hills may be found in my work on Lake Superior.
