38 
MUSEUM BULLETIN NO. 25. 
curves of a rooster’s tail feathers. Some of the described species 
of Taonurus are probably of current rather than plant origin. 
Typical examples of fossil current mark are common in the lower 
part of the Joggins section, N.S., at the old grindstone quarry. 
The Aylmer sandstone at Ottawa is nearly always characterized 
by these impressions. Plates XXXI and XXX II I show examples 
of current mark from the lower part of the Joggins section. 
DEPTH TO WHICH RIPPLE-MARK EXTENDS. 
The discussions of ripple-mark found in many texts and treati- 
ses on general geology treat them as shallow water features. 
LeConte 1 states that “By means of these characteristics of shore 
deposit (ripple-marks) many coast lines of previous geological 
epochs have been determined.” A bulletin of the United 
States Geological Survey, intended primarily for use in schools 
and colleges, informs the student that: “In the water they 
(ripple-marks) are formed only where it is shallow and they do 
not extend beyond the depths to which the water is agitated 
by the wind .” 2 Fossil ripple-mark has thus come to be regarded 
by many geologists as a criterion of very shallow water condit- 
ions. This conception of ripple-mark has no doubt arisen chiefly 
through the fact that direct observation of it has been limited 
to shallow water. But we have little better reason for assuming 
that ripple-mark extends no deeper than it has been actually 
seen, than we have for inferring that the natural habitat of 
fishes extends no deeper than we have actually observed them. 
Curiously enough the statements regarding ripple-mark 
contained in some of the older text books are much more accurate 
than are discussions of the same subject in many of the more 
recent manuals. Thus the statement of Jukes regarding ripple- 
mark produced by current action requires no revision at present. 
He writes: “A rippled surface, therefore, to a rock, is no proof of 
its having been necessarily formed in shallow water, though 
rippled surfaces are perhaps more frequently formed there, 
but simply a proof of a current in the water sufficient to move 
1 Elements of geology, 1888, p. 3a. 
1 J. S. Diller, "The educational series of rock specimens collected mad distributed by the 
U. S. Geol. Survey," Bull. U.S.G.S.. No. 150, 1898, p. 82. 
