GEOLOGICAL IMPORTANCE OE SEDIMENTATION 321 



taken as indications of the presence of ancient seas. Numerous 

 instances illustrating this tendency could be cited from the writings 

 of the leaders of the science, but a single illustration will suffice. In 

 1893 Bailey Willis contributed a most valuable article to the Journal 

 0} Geology, entitled "Studies for Students: Conditions of Sedimentary 

 Deposition." It is because of the originality and value of this writer's 

 numerous geological articles in general, and of this one in particular, 

 that it is chosen for illustration. In this article sedimentation is 

 defined as follows: "Sedimentation consists of three sub-processes — 

 sorting, distribution, and deposition. These are effected by waves 

 and undertow, tides, winds, and oceanic currents."^ 



While lacustrine deposits could be included under this definition, it 

 leaves no place for fluviatile sedimentation, and of course does not 

 pretend to include sorting, distribution, and deposition by the wind. 

 While it would hardly have been within the limits of this one article 

 to have treated fully of these land deposits, yet it is noticeable that in 

 the introductory pages no mention is made of them, and sedimenta- 

 tion is repeatedly referred to as pertaining to the sea, rock disinte- 

 gration and decomposition to the land, while the streams are men- 

 tioned as the carrying agents which sweep the sediment to the sea.^ 



In the above-mentioned article the subject of marine sedimenta- 

 tion is ably treated, especially noteworthy being the dependence indi- 

 cated between the relation of the sediments upon both the activities 

 of the ocean and the topographic character of the land. The present 

 article aims to treat of some of the general relations of marine and 

 continental sedimentation, and to partially indicate how these rela- 

 tions may be expected to fluctuate with the extent, topography, and 

 climate of the continental masses. It may be considered, therefore, 

 as supplementary to the above-mentioned article on the conditions 

 of marine sedimentary deposition. 



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 familiar with the Tertiary and Recent deposits 

 within the interiors of Asia and America. 



While the importance of land deposits has, during the past decade, 



^ Vol. I, pp. 476-520. 2 Loc. cit., p. 480. 3 Ibid., p. 480. 



