A new areal map of the pre-Cambrian and related rocks of the Reading Hills near the Lehigh County-Berks County boundary is presented.

Structure sections, based on the interpretations of different workers, are given. The problem of the origin of jasper, found abundantly in the region, is discussed.

The following two theories of origin of the area are examined in the light of the evidence of the areal maps and structure sections, and the information obtained from wells, mine shafts, and past diamond drilling:

  1. Overthrust faulting of several miles thrust followed by normal faulting, folding, and erosion have brought about the present relationships.

  2. Folding and normal faulting (with thrust faulting appearing locally), followed by erosion have been the dominant factors resulting in the present conditions.

It is concluded that the second theory is the more applicable.

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