Page:Popular Science Monthly Volume 65.djvu/157

Rh incurring serious loss to the federal army. Its consideration is also appropriate in tin's article, since the plans of the commanders and the movements of their forces were very largely controlled by the physiography of the plateau.

So deeply dissected is this plateau that, without exception, military writers speak of it as the Cumberland 'Mountains.' Weathering and stream work, continued through untold ages, have cut deep valleys and carved hills until we have the present rough country to cross which, even without an enemy in front, was no small undertaking. The soil, derived from Carboniferous sandstone in general is a thin sandy loam,

and only in the valley bottoms where the streams have worn a trench and partly filled it with alluvial sediment is the soil fairly fertile.

The plateau descends towards the plains of middle Tennessee by three great irregular terraces each roughly about five hundred feet high. Through these terraces streams have carved narrow valleys through which the roads pass to the lowlands. These gorges, called 'gaps' by the mountaineers, were as important to the armies in that section as were the 'wind gaps' between Virginia and the Shenandoah valley to the confederates. They were easy to hold with a small force against a numerous body of the enemy and were especially serviceable to a retreating army, since a small rear guard was able to give complete protection.