The folded Appalachians are paralleled by an eastern "hinterland" of intensely dislocated and metamorphosed crystalline rocks. Fossils have not been found and the area has not been studied in as much detail as is desirable. This is due to its seemingly hopeless composition of uniformly crystalline rocks, poor exposures and the great attraction exerted by better exposures and more spectacular geologic objects farther west.

The age of the crystallines is largely undetermined and they may be either basement of the appalachian geosyncline and its folds or their highly deformed crystalline axis. Some of the crystallines--the Baltimore gneiss and its equivalents--seem to be pre-Cambrian but most of the overlying metamorphics probably belong to the crystalline axis and the lower Paleozoics. The pressing problem is the determination of age relationship and thus the extent of what may be called a basement.

If a preliminary division of the crystalline axis into a basement and an overlying metamorphic series is accepted it is readily seen that the trends of the crystallines above deviate from those of the basement below. The gneiss appears in elongate and well defined uplifts of limited size and generally showing dominating vertical components whereas the schists seem to have moved forward and were possibly thrust over less metamorphosed Paleozoics following the general Appalachian trends.

There is no major break and no unconformity between the fossiliferous Paleozoics and the schist but a gradual southeastward increase of the intensity of metamorphism. The parallelism of structures is striking.

Appalachian folds within the crystalline axis are generally overturned northwestward but at numerous places virgation is southeastward.

The crystalline axis exerts a very strong influence on the overlying folds. Cleavage dominates, folds are overturned uniformly and this domination reaches as high as the Ordovician in some parts of the lower Paleozoic section. Farther away from the axis this influence declines and folding becomes more symmetrical, less uniform and at many places locally influenced by individual folds and their elements.

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