RECENT AND FOSSIL RIPPLE-MARK, 
29 
Depth of water. Amplitude of ripple-mark. 
15 in .2 to 4 in. 
2J ft. 3J to 4 in. 
10 ft 4 to 6 in. 
lift 44 in. 
20 ft * 4 to 5 ft. 
The large number of observations which have been made 
on ripple-mark in depths between 6 inches and 10 feet may be 
summarized in the statement that the amplitude at the former 
depth varies between 1 and 2 inches and at the latter between 
3| and 6 inches. Ripple-mark with an amplitude of less than 
2 inches is, so far as my observation goes, formed only in water 
having a depth of less than one foot. 
It is probable that the factors controlling amplitude and 
height of crest in symmetrical ripple-mark include coarseness 
of sand, depth of water, and wave amplitude. Much additional 
work is needed to determine the relative importance of these 
factors. 
RIPPLE-MARK OF IMBRICATED OR COMPLEX PATTERN. 
The more simple and common forms of ripple-mark are 
included in the two types which have already been described. 
The more complex forms resulting from various combinations 
of these fundamental types will now be considered. Ripple- 
mark of simple type is often modified by the superposition upon 
it of another type thus producing a complex or complicated 
pattern. The relationship of the different features of these 
complex forms of ripple-mark to the factors producing them 
has been ascertained in many cases by observation of them as 
they emerge from the ebbing tide. 
Ripple-mark developed by current action is frequently 
modified by wave action. If the wind should blow at right 
angles to the course of a stream in which current mark is forjning, 
or transverse to the direction of a tidal current, the ripple-mark 
resulting from these currents will be crossed transversely by 
ripple-mark which trends at right angles to the course of the wind. 
If the waves are the product of a moderate breeze and are of 
small size the current ripple-mark will be marked on its gentle 
slopes only by a miniature ripple-mark pattern which will be 
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