10 
MUSEUM BULLETIN NO, 25, 
dry for sand grains to roll freely the whole surface of a sand dune 
to a depth equal to the elevation of the ripple-mark crest above 
its trough moves forward through the progressive movement of 
the hundreds or thousands of ripple-marks which cover it. The 
rate of movement of the ripple-mark depends on the size of the 
grains and the velocity of the wind. Observations on the dune 
sand east of Wellington showed the ripple-mark during a gentle 
breeze to be advancing with it at the rate of 4| inches per hour. 
At Port Colbome on lake Erie measurement of the movement 
of wind ripple-marks made in connexion with anemometer 
readings showed the ripple-mark to be moving at the rate of 24 
inches per hour with a wind velocity of 12*9 miles per hour. 
This ripple-mark had an amplitude of 3| to 5 inches with a depth 
of about | inch. 
The size or amplitude of wind ripple-mark varies but little 
with variation of wind velocity. The variations in amplitude 
noted in measuring some hundreds of examples on the dunes 
near Wellington all fell between 2 and 4 inches. The height of the 
crest above the trough in all of these was very close to | inch. 
Although variation of wind velocity appears not to affect the 
amplitude of the ripple-mark its rate of advance is directly 
proportional to it. My observations with reference to the 
slight variation in the amplitude of sand ripple-mark within the 
limits of an area of the same degree of fineness of sand grains 
coincide with those of W. W. Strickland who states that “The 
first thing to be observed about them is that they are nearly all 
the same size, viz., about 3| inches from crest to crest.” 1 
W. Harding King 2 who has studied dune ripple-mark in 
desert regions writes: “So far as I have seen the ordinary rippling 
on a dune never develops much beyond 4 inches in average 
length.” 
The principal factor controlling the slight amount of vari- 
ation which is shown by the amplitude, appears to be the coarse- 
ness of the sand. The crests of wind ripple-mark at Sand 
Banks on lake Ontario were found to be separated by intervals 
of from 2 to 4 inches. 
1 “Notes and observations on forms of sand,” pp. 1-36, 32 figs., 1915, p. 16: R. H. Smithson 
and Blanchard, London. 
s W. J. Harding King, “The nature and formation of sand ripples and dunes,” Gaog. 
Jour., vol. XLVII, 1916, p. 191. 
