RECENT AND FOSSIL RIPPLE-MARK. 
11 
At Port Colborne on lake Erie, with the exception mentioned 
below, they varied in amplitude between 3| and 5 inches. The 
sand at the latter point is slightly coarser than at Sand Banks. 
A wind gap about 80 yards wide and 60 feet deep has been cut 
across the sand ridge which borders the north shore of lake 
Erie one-half mile west of Sugar Loaf sand dune. Near the lake 
end of this wind gap the sorting action of the wind has left some 
very coarse sand on the lower part of an up-slope. Wind 
ripple-mark of a very rude type was observed on this coarse 
sand. The ridges were quite irregular in their trend as well as 
parallelism. The troughs were about 10 inches apart and one- 
third inch in depth. These observations appear to show that 
the amplitude increases with the coarseness of the sand. This 
was the conclusion reached by Sokolow 1 who found that the 
height and amplitude of the ripples vary with the size of the sand 
grains. 
In the case of very coarse sand ordinary wind velocities 
either produce no ripple-marks or very irregular ones. Occas- 
ionally when both coarse and fine sand are present, examples of 
ripple-mark may be observed in which the coarse sand or fine 
gravel grains occupy the crests of the ripple-mark while fine sand 
comprises the slopes. Ordinarily, however, no distinction in 
the coarseness of the material of the slopes and the crests can 
be recognized in the lake Ontario and lake Erie dunes. 
A unique variety of ripple-mark formed on highway dust 
by artillery fire so directed that the shells from the guns passed 
at a slight elevation above the road has recently been described. 2 
The ripple ridges are reported to be one-half inch apart, 
much closer than they are ever formed in sand. They were 
produced according to the observer by the explosive wave passing 
over die road during the action of the field guns. 
The most striking characteristic of wind-made ripple-mark is 
the very slight elevation of the ridges as compared with the height 
of the crests of ripple-mark made under water (Figures 2 and 3). 
This difference is clearly shown by a comparison of the ratios 
1 Die DOnnen, Biltiung, Entwickdung und Innerer Bau. Deutsche vom Verfasaer 
Erg&nzte Ausgabe von Andreas Arzreni, Berlin. 
* The formation of dust-ripples by H.U.G. (C.F.), Nature, vol. 97, p. 530, 1916. 
