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T H E 



AMERICAN JOURNAL OF SCIENCE 



[FOURTH SERIES.] 



Aet. XXVII. — The Nature of Paleozoic Grustal Insta- 

 bility in Eastern North America; by Chaeles 



SCHTJCHEET 1 



It is now three years since Professors Eliot Black- 

 welder and Rollin T. Chamberlin began a correspondence 

 with the writer looking toward a time when we three 

 might offer a nomenclatorial scheme expressive of onr 

 conclusions regarding the dias trophic epochs and their 

 classificatory relations that would be acceptable to geolo- 

 gists. In the meantime the Great War came on and our 

 contemplated joint efforts have as yet come to no visible 

 results. However, as the writer has long been interested 

 in the times of earth movements and their classification 

 into minor and major crustal deformations, he was stimu- 

 lated by this correspondence to apply himself more vig- 

 orously to gathering the evidence of the times of diastro- 

 phism, and especially in the eastern and mid-continent 

 regions of North America. Many interesting results 

 have been attained, but the data at hand are not fully as- 

 sembled or completely understood. Therefore this pre- 

 sentation is of a preliminary character, and in the nature 

 of a report of progress. 



In addition to various terms that have been proposed 

 from time to time for North American crustal deforma- 

 tions, there are now in print three distinct and different 

 tabulations of the known orogenic periods. The first of 

 these appeared in June, 1914, and was by R. T. Chamber- 

 lin. 2 The second, by Eliot Blackwelder, 3 was written be- 



1 Presented before the Geological Society of America at its meeting in 

 Boston in December, 1919. 



2 Jour. Geology, 22, 315-345, 1914. 



3 Ibid., 633-654. 



Am. Jour. Sci.— Fourth Series, Vol. L, No. 300.— December, 1920. 

 30 



