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"certain combinations of amplitude and frequency" the largest ocean 

 waves might produce ripples having a length equal to half the height 

 of the wave. The supposed giant ripples observed at Lockport, N. Y., 

 reached a length of thirty feet, implying waves sixty feet high in the 

 Medina sea. Fairchild explains the same features as spits or rather 

 beach ridges, sometimes observed in series of as many as four crests 

 with intervening troughs. Of the fifteen halftones with which the 

 article is illustrated, about one third are clear enough to show without 

 doubt that the features referred to are of the same nature as those dis- 

 cussed and figured in Gilbert's article. Four of the cuts show sand 

 ridges on the present shore of Lake Ontario which are supposed to 

 exemplify the process by which the features in the Medina were made. 

 The remaining cuts and a few expressions in the article leave it in 

 doubt as to whether the features observed were all of the type from 

 which Gilbert's conclusions were drawn. The latter found no inter- 

 vals of more than thirty feet from crest to crest ; the article under dis- 

 cussion refers to similar spacings of eighty feet. Gilbert's discussion 

 of the features as ripples implies a symmetry or at least unity in the 

 trough by which its breadth could be fairly estimated when only a 

 portion could be seen. Fairchild speaks of the trough as only a 

 "negative or passive element" which may have any width varying 

 with the accidents which determine the location of a new beach ridge. 

 The observations of both, and both interpretations, involve abundant 

 cross bedding. Itwould seem that the two processes hypothesized would 

 produce different dispositions of this crossbedding, as well as differ- 

 ences in the symmetry of the trough. Gilbert shows by diagram the 

 necessary arrangement of the crossbedding under various suppositions 

 as to the shifting of the ripple system during deposition. It is quite 

 improbable that the patterns in vertical cross section thus produced 

 would be duplicated in a series of beach ridges. In the latter case the 

 lamination on the landward side of an outer ridge should be plainly 

 distinguishable from the lamination on the lakeward slope of the next 

 ridge within. The lamination corresponding to this latter slope should 

 disappear only in the most extreme cases of landward migration of 

 the ridge, a condition quite improbable where a series of ridges is pro- 

 duced. Fairchild's objection that ripple marks are not found of 

 intermediate sizes between eight inches and the "giants" is certainly 

 of interest. 



N. M. F. 



