RECENT AND FOSSIL RJPFLE-MARK. 
33 
Other observations of Mr. Gilbert 1 on ripple-mark of complex 
pattern are as follows : ‘ ‘While at the seashore in the summers of 
1911 and 1912 I visited almost daily a sand spit bare at low tide 
and saw each day a new pattern of ripple-mark. Cross patterns 
were common— or rather not rare — but only a few of them 
indicated equal action in two directions. Usually a system of 
parallel ridges was given an appearance of reticulation by 
Figure 5. Entrance to Squam estuary, Mass., with section along A B. Heavy 
Unes, high water; dotted lines, low water. The figure illustrates con- 
ditions under which ripple-mark shown in Plate XIV was developed. 
systematic offsets the lines of offsets making 60 degrees with the 
trend of ridges. As the lines of offsets were not equally spaced 
I did not refer them to a crossing system of water waves. Occas- 
ionally there were two systems of offsets producing a pattern 
with three directions. Not rarely the crests of the ridges were 
1 Letter of Dec. 12, 1913. 
