Recent studies have been fruitful in bringing to light new evidences of diastrophism. The older terranes have been found to be more and more intricately deformed, as inquiry proceeds. The later terranes have disclosed overthrusts of unexpected extent and frequency. Troughs of graben type have been found to form chains of almost continental length. The recognition of unconformities has been multiplying to an embarrassing degree. Moreover, as inquiry passes from local and regional fields to the greater features of the earth, the continents and the oceanic basins it discloses evidences of a profound order of diastrophism whose significance has been only meagerly recognized in the past. In the light of these revelations, it is important to workers in this difficult field to know whether sufficient resources of diastrophism support all the types of interpretation that are currently offered for acceptance. If the dynamic resources that form the groundwork of . . .

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