Fig. 6. Precipitous Cliffs along the Northwestern Side of the Wilmington Notch—illustrating the northeast and southwest type of fault valley.
depressions were recognizable. The old valleys have gentle slopes and wide expanses. Their contours are softened down and the whole physiographic expression is one which suggests long-continued erosion and maturity of form. In studying out these relations, one has also to eliminate as far as possible the mask of glacial drift which is everywhere in evidence. The valleys of the old system run in their most marked development east and west, and north and south. Several of them are occupied to-day by some of the largest streams and lakes—such as Schroon lake, the southern third of Lake George, parts of the Hudson Valley and several tributary to Lake Champlain. One half of an old valley will often remain with characteristically gentle slope and mild topography, while the other half of the depression will consist of the steep precipices of the next type. And as the second type has been superimposed upon the first, the observer is often forced to trace the former out despite its disguises and modifications.
The second type of valley is obviously the result of faulting, and of faulting that is of no great geological antiquity. The sides and steep escarpments and the depressions may have all the characteristics of a 'Graben-senkung,' or of a fjord, if the latter can be imagined away from the sea. In the southeastern portion of the mountains as well as in the interior, three pronounced sets of fault escarpments may be recognized and plotted. The most marked one is northeast, and to it is due the general northeast and southwest trend of the mountains. The topographic maps, and still more the relief model prepared by
