WORK OF JOSEPH BARRELL OX SEDIMENTATION 31 



Barrell was evidently impressed by the features of certain formations 

 with which he became familiar during this period of his life ; these forma- 

 tions were the Triassic deposits, the Mauch Chunk shale, and the over- 

 lying Coal Measures, the Pocono sandstone, and the deposits of the 

 Catskill group. The current interpretations of the conditions under 

 which and the processes by which these deposits were formed did not 

 satisfy him. Furthermore, there were the great problems of the forma- 

 tion of the geosynclines in which the deposits were laid down, the former 

 extension of the deposits, and the sources of the materials composing the 

 deposits, all of which led to the consideration of the orographic history 

 of the northern Appalachians and their degradation and the origin of 

 the Continental Shelf of eastern North America. The experiences in 

 eastern and central Pennsylvania unfolded to Barrell problems to the 

 solution of which he assiduously set to work. 



Barrell's Investigations of the Principles of Sedimentation 



GENERAL OB.SPJRVATIOXS ON BARRELL'H WORK 



The first paragrapli in the second one of Barrell's longer j^apers on 

 sedimentation, "The origin and significance of the Mauch Chunk shale," 

 is as follows : 



"A discussion of tlie nature of geographic and climatic control of sedimenta- 

 tion has been previously made by the writer in order that the origin of certain 

 specific formations might be dealt with, and the present paper on the interpre- 

 tation of the Mauch Cliunk follows these previous articles in logical sequence.'" ' 



A quotation from the article referred to in the footnote is as follows : 



"As pointed out by Walther in 1893, although all geologists are familiar with 

 the occasional extensive deposition of land-waste upon the land as among the 

 results of geological activities at the present time, yet the prevalence of ero- 

 sion on the land and of sedimentation beneath the sea has governed the inter- 

 pretation of nearly all ancient sedimentary deposits. It has ordinarily been 

 accepted as a geological principle, that ancient continental surfaces are only 

 determined by unconformities, while, on the other hand, all sediments, unless 

 obviously deposited by fresh waters, as proved by their organic contents, are 

 taken as indications of the presence of ancient seas. 



"As showing exceptions to this tendency to neglect the deposits, formed upon 

 the land must be noted the work of the geologists of the Indian Survey for 

 the past thirty years, and that of other geologists who have been most famil- 

 iar with the Tertiary and Recent deposits within the interiors of Asia and 

 America." 



^ Relative importance of continental, littoral, and marine sedimentation. .Tour. Geol., 

 vol. 14, 1906, pp. 316-350, 430-4.57. 524-568. 



