Page:Popular Science Monthly Volume 68.djvu/207

 Rh down moderate slopes from the northwest, against high and sparsely wooded precipices on the southeast and join larger streams which flow northeast or southwest. When a wide area is studied, it is only the older and still surviving east and west or north and south valleys which break up this lattice-like regularity.

In less frequent occurrence than the northeast and northwest fault breaks, minor ones ranging nearly due north may be recognized—but they do not exercise so important an influence on the general relief.

The three systems of faults have in some instances led to great single precipitous escarpments suggesting that the movement was chiefly confined to one single plane, but it is much more common to find the fault a compound one. That is, a very steep mountain face will consist of a series of small escarpments, each with a bench at its foot. These benches make terraces, and on Lake George one can easily see, even when the mountain is thickly forested, that the trees are growing in pronounced rows with thinner lines of vegetation between. A mountainside may thus look like a gigantic series of furrows, as is true of the ridge from Black Mountain to Elephant Mountain. Where the faults cut across a projecting shoulder the terraces go up one side and down the other like a series of lunettes. Forest fires and the lumberman's axe, while destroying much of the beauty, have yet brought out these features with striking emphasis, and when the light intensifies the relief with shadows they appeal to the observer in the strongest way. The narrow ridge between Lake George and Lake Champlain contains some of the roughest country in all the Adirondack region.

The faults and their escarpments were doubtless much freshened up by the Labradorean ice-sheet which plucked away from their faces the loose rock, sheeted by the parallel faults. In this way the relief was heightened during the Glacial epoch, and its freshness and youth still remain to us, but the faults preceded the ice and were the great governing factors. Thus far no evidence of post-glacial faulting has been observed.

On the south side of the mountains the faults run out in a striking way into the overlapping Paleozoic areas and have been traced as much as thirty or forty miles. One famous one causes the Precambrian rocks on the west to abut sharply for thirty miles against the Cambrian and Ordovician strata, forming an escarpment which faces east. After the Precambrians have disappeared below the Paleozoics for two miles, they rise again into view at the pass called the 'Needles,' where the Mohawk river, the Erie Canal and the New York Central and West Shore Railways find a way close together fifty miles west of Albany. Another is responsible for the Precambrian outlier of Little Falls, recently described by Professor H. P. Cushing. The displacements