Uplift permitted renewed erosion to wear away the soft belts, leaving mountain ridges of hard rock separated by parallel valleys.
It was carried off in carts to open spaces, where an exposure of some weeks to the air was found to pulverize the hard rock far more efficiently than the old method of crushing with mallets.
It is one of the most rapid and economical which can be employed in soft formations, but where hard rock is encountered it is almost useless.
A quartz vein or bed of hard rock may show itself as a sharp ridge or as a well-defined bench; a stratum of soft rock or the line of a great fissure, or the weakening of the strata by an anticlinal fold, may produce a ravine or a deep valley.
Where the hard rock does crop out on the surface, it is so excessively weathered as to be with difficulty recognized as rock at all.
The land pebble is worked in central South Florida; the hard rock chiefly between Albion and Bay City.
From the morphological point of view it is more important to distinguish the associations of forms, such as the mountain mass or group of mountains radiating from a centre, with the valleys furrowing their flanks spreading towards every direction; the mountain chain or line of heights, forming a long narrow ridge or series of ridges separated by parallel valleys; the dissected plateau or highland, divided into mountains of circumdenudation by a system of deeply-cut valleys; and the isolated peak, usually a volcanic cone or a hard rock mass left projecting after the softer strata which embedded it have been worn away (Monadnock of Professor Davis).
The general character of the landscape in the Eastern Division is a succession of steep escarpments formed by the edges of the outcropping beds of harder rock, and long gentle slopes or plains on the dip-slopes, or on the softer layers; clay and hard rock alternating throughout the series.