141 The Petrography and Genesis of Sediments 



the differences. Bed 2 (sample 5, fig. E, p. 169) is of the well-sorted type 

 produced by strong wave action or by wind ; bed 3 (sample 6, fig. F, p. 169) 

 shows a remarkable resemblance to the poorly-sorted lagoonal type repre- 

 sented in E, p. 170. 



The facies of bed 3 (sample 6) is therefore easily recognized; it was 

 formed not in the open sea but in a more enclosed body of water, a 

 lagoon, or perhaps an estuary or an arm of a bay like Chesapeake Bay of 

 to-day. But bed 2 (sample 5) is harder to place. Mere comparison of its 

 diagram (E, p. 169) with the diagrams on p. 170 shows a resemblance to 

 diagram J even more striking than that of F, p. 169, to E, p. 170. This 

 does not necessarily mean that bed 2 was wind-deposited. Its general con- 

 forming to the rest of the section with transition probably at bottom as 

 well as at top (in any case a more argillaceous composition in its lower 

 part), and the fact that no striking rounding of the quartz grains was 

 noted, are against this interpretation. The discrepancies can be adjusted 

 if it be assumed that the difference between diagrams of wave-sorted mate- 

 rial, like C, p. 170, and wind-sorted material like J, p. 170, is more funda- 

 mental than mere difference between action of water and air, and repre- 

 sents rather the different effects of wave and current action. That is, a 

 current of water might produce the same sorting shown in E, p. 169, as 

 was produced in J, p. 170, by a current of air. 



Theoretical considerations lend support to this conclusion. For 

 the action of waves consists essentially in a prolonged working over of 

 material of a certain maximum degree of coarseness depending on the 

 average uniform conditions under which material is supplied to them. 

 From this they tend to eliminate all the finer material, producing a 

 concentration of the coarsest. Even though their strength is constantly 

 fluctuating the end result of their work is the product essentially of their 

 maximum force. But a current is an actively depositing agent, and while 

 it will also tend to eliminate all material that is fine enough to be carried 

 by it, the sorting it produces will be rather the result of its mean strength 

 corresponding to a certain fineness of material which would be accumu- 

 lated too fast to be accessible for reworking by its maximum strength. 

 Hence the coarsest material brought in during periods of maximum 



