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MUSEUM BULLETIN NO. 25. 
tidal currents. A set of beds which have been laid down in a 
zone characterized by sand-wave formation may not preserve 
the outlines of any single set of sand waves but the steep foreset 
beds which are formed as these waves travel with the current 
will be preserved as the familiar cross bedding so common in 
many coarse sandstones. Cross bedding is thus characteristic 
of both river and tidal current laid beds. The direction of the 
inclined beds in the river deposits should, however, possess a 
degree of uniformity not shared by those which have been 
produced in marine deposits under the influence of a current 
which daily reverses its direction. The variable direction of the 
cross bedding in marine elastics should serve to distinguish 
them from continental river laid beds. 
Cross bedding on a much finer and smaller scale than that 
developed in connexion with sand waves may characterize 
sandstones formed under water velocities suitable for the for- 
mation of ordinary asymmetrical ripple-mark. J. E. Spurr 1 
and T. A. Jagger, jun., 2 who held different views of the subject, 
have very fully discussed this type of structure. 
1 Spurr, J. E. “False bedding in stratified drift deposits,” Am. Geol., vol. XIII, 1894, 
pp. 43-47. "Oscillation and single-current ripple-marks,” Ain. Geol., vol. XIII, 1894, pp. 
201-206. 
s Jagger, T. A„ jun., “Some conditions of ripple-mark,” Am. Geol., vol, XIII, 1894, pp. 
199-201. 
