RECENT AND FOSSIL RIPPLE-MARK. 
5 
modes of formation ripple-mark may be classified as current 
ripple-mark, wave ripple-mark, and ripple-mark resulting from 
combinations of these two fundamental types. Dune ripple- 
mark is the product of air currents and belongs in the first men- 
tioned class. This subaerial form of ripple-mark is distinguished 
by well marked features from subaqueous ripple-mark. 
FIELD WORK AND METHODS. 
Parts of three field seasons have been devoted to the accumul- 
ation of the data on which this paper is based. The field 
observations have been made chiefly along the shores of lakes 
Ontario, Erie, and Deschenes, and the bay of Fundy. A few 
days were also spent in studying ripple-mark phenomena along 
the St. Lawrence river between Montreal and lake St. Peter. 
Through the courtesy of Mr. H. L. Cole of the Mines Branch, I 
had the use, during the St. Lawrence River studies, of quarters 
on a launch which had been chartered for the purpose of investi- 
gating, from the economic standpoint, the sand deposits along 
the St. Lawrence river. Much of the field work has been taken 
up for periods of a few days or weeks when expeditions planned 
primarily for researches in stratigraphic palaeontology have made 
easily accessible areas favourable for ripple-mark studies. 
In both field and office work, E. J. Whittaker has furnished 
invaluable assistance. 
A primary object of the field work has been to get a precise 
knowledge of the shape and physical features of ripple-mark as it 
exists under water where it is formed, and of the special conditions 
under which different types are developed. Such information 
concerning bottom features as the observer can obtain by looking 
through the water from a boat is subject to the same limitations 
as are his observations of fish and other forms of subaqueous life. 
The naturalist fortunately has his dredge but it affords no aid 
in the study of ripple-mark. I have, however, found it possible 
by means of plaster of paris to secure perfect moulds of ripple- 
mark in which the finest details of contour are preserved without 
the slightest distortion or compression. By this means exact 
duplicates in plaster of the various types of ripple-mark which 
occur on lake, stream, and sea bottom have been obtained for 
