Page:The Journal of geology (IA journalofgeology11893univers).pdf/55
by the relation of volume of sediment to the force of waves or currents. If the analysis be based on the sub-processes and conditions which favor them, it may be stated and discussed as follows:
SORTING.
The conditions under which sorting is more or less efficiently carried on are three in number.
Favorable conditions:
- (a) Vigorous wave action accompanied by strong undertow.
- (b) Prolonged transportation in consequence of deep water and continuous currents.
- (c) Moderate volume of sediments.
The conditions under which sorting is not accomplished are the reverse of these, namely:
Unfavorable conditions:
- (a) Feeble or diffused wave action.
- (b) Concentrated deposition.
- (c) Excessive volume of sediments.
It will be profitable briefly to discuss these positive and negative conditions.
(a) Vigorous wave-action.—The force of waves is determined by their fetch and the strength of winds. In the study of modern beaches the latter is important, since it controls the form and the greatest storm[1] fixes the maximum size of detritus moved; but in considering fossil beaches as strata we deal with sands which have been so rearranged during submergence that the beach form is lost. However the former condition, the fetch of the waves is more constant, and the force of the waves determined by it may be inferred from the nature of the beach deposits.
The efficiency of waves of a given force is determined by the concentration of their blows, and this is conditioned by the slope against which they break. If relatively deep water prevails
- ↑ For full discussion of wave erosion and deposition, see Lake Bonneville, by G. K. Gilbert.Monograph 1, U. S. C. S.