REVIEWS F 195 
altitudes of from goo to rioo feet, and another altitudes of from 1500 
to 1700 feet. (3) The Eastern type comprises the Unaka Mountains 
and the western portion of the Piedmont Plain. 
The formations of this region are divided into two groups: (1) The 
unaltered sedimentaries which are of varying degrees of hardness and 
solubility, and (2) the metamorphic and igneous rocks. 
The twenty-three formations of the Paleozoic are divided into five 
subgroups : (1) The lowest six Cambrian formations consist of con- 
glomerates, quartzite, and siliceous shales, and are nearly insoluble. 
These form the rocks of the Eastern division. (2) Ten Cambrian and 
Silurian formations, composed for the most part of limestone and 
shales, are relatively soluble. ‘These occupy the greater part of the 
Valley or Central division, while a few beds of sandstone and the Knox 
dolomite give rise to the valley ridges. (3) The Upper formations of 
the Silurian and the formations of the Lower Carboniferous are the 
rocks which form the Highland Rim, and also some of the valley 
ridges. (4) On account of their solubility, the Lower Carboniferous 
series gives rise to the characteristic topographic forms in the Western 
division. (5) The durable Coal Measures conglomerates cap the Cum- 
berland plateau and have occasioned the preservation of large areas of 
its surface. 
The second group of rocks, that is, the igneous-metamorphic 
group, comprises, (1) the feldspathic (easily eroded) rocks which form 
the larger part of the Piedmont plateau, and (2) the non-feldspathic 
(resistant) rocks which have given rise to the irregular topography of 
the Unakas. 
In this region Hayes makes out three peneplains or base levels, 
namely, the Cumberland base level, the Highland Rim base level, 
and the Coosa base level. 
The altitude of the reconstructed Cumberland base level at its 
southern edge is about 1200 feet. From this altitude it increases to a 
height of 2000 feet in the central part, and decreases again to 1600 
feet along its southern and eastern edges. This gives a gradient of 
ten feet per mile from the edges to the center, which is steeper than a 
base level grade should be, and, besides, no base level tract should 
have such a shape unless drainage radiated from its center, and this 
does not seem to have been the case. Hayes explains the present form 
by the hypothesis that in being elevated to its present position the 
base leveled region was warped into the form of alow dome. Upon, 
