AGE OF THE ROCKS. 
29 
only one of — many other similar folds. In regions of intense movement isoclinal or over- 
turned folding is very common. It seems probable that almost or quite the whole of the 
area has been subjected to repeated folding, with axes trending in a northeasterly direc- 
tion. Prevailing isoclinal folds would account for the predominant northwesterly dips, 
while southeasterly dips could be explained by the presence of more nearly symmetrical 
folds, like the Blacksburg anticline. Thrust faulting may also have taken place. Such 
an explanation accords with the accepted idea of structure elsewhere in the Appalachian 
province, where conclusions can be more safely drawn. Careful and detailed study will 
be required to prove the truth or falsity of this hypothesis. 
At one place the structure is worthy of mention. The "Monroe" beds, southwest of 
Monroe, N. C, are very well bedded and in most places have only small dips. In several 
places cuts along a new road expose a structure illustrated in fig. 2. The beds are bent 
up as if by a thrust from below and are broken and crushed. The material in the crushed 
zone is of the same character as that of the beds. This structure resembles the products 
of some of Willis's a experiments in the folding of sediments. It is a fold-fault produced 
by compression, and probably results from expansion of the beds due to atmospheric 
alteration. 
Scale of feet 
12 3 4- 
FlG. 2.— Sketch of exposure along road west of Monroe, N. C, showing disturbance of " Monroe " beds. 
a, Soil; b, disintegrated tuff; c, volcanic tuff. 
AGE OF THE ROCKS. 
Almost from the beginning of geologic study in this region the age of the rocks has been 
the subject of much investigation and speculation. The earlier workers found slight 
encouragement in the results of their labors, and it must be admitted that our views have 
advanced very little beyond theirs. It used to be supposed that practically all the ore 
deposits of these Southern States were contemporaneous in origin with the inclosing rocks. 
Attention was therefore directed principally to the metamorphic rocks, in which most of 
the deposits of economic value occur. 
METAMORPHIC ROCKS. 
From their crystalline structure and the absence of organic remains these schistose rocks 
were first supposed to represent part of the original crust of the earth and were called 
primitive or primary. Emmons b in his report of 1856 considered these rocks as the old- 
est sediments of the globe and placed them at the base of the Paleozoic, in what he called 
the Taconic system. On the basis of what he supposed to be fossils, he concluded that 
a Willis, Bailey, The mechanics of Appalachian structure: Thirteenth Ann. Rept.'U. S. Geol. Sur- 
vey, pt. 2, 1893, Pis. LXXV, a'; LXXXII, e. 
b Emmons, E., Geol. Rept. Midland Counties of North Carolina, 1856, pp. 41-45, 60-64. 
