6 
MUSEUM BULLETIN NO. 25. 
office study, and comparison with a considerable collection of 
fossil ripple-mark. The collections which have been acquired 
during the progress of the work include a fine slab of ripple- 
marked Berea sandstone from Ohio which was presented to the 
Museum by Prof. C. S. Prosser, and specimens of Cambrian 
sandstone ripple-mark from northern New York collected and 
presented by Mrs. Orra P. Phelps. I am also indebted to Mrs. 
Phelps for valuable photographs and profiles of Cambrian 
ripple-mark. Several members of the Geological Survey have 
contributed interesting specimens of fossil ripple-mark to this 
collection. The most important part of my own collection of 
fossil ripple-mark was secured at the Joggins section of the Nova 
Scotia coal measures. The plates of ripple-mark profiles in this 
paper and many of the photographs have been made from the 
plaster of paris duplicates of recently formed ripple-mark which 
have been made during the progress of the field work. 
Where the water over the ripple-mark is very shallow — one 
foot or less — the process of taking a mould is very simple. Any 
box of convenient size may be used for the mould by knocking 
out the bottom and cutting the edges which are to be pressed 
into the ripple-marked sand to a bevel edge in order to produce 
the minimum disturbance of the beds. A size 10 by 16 or 18 
inches has been found convenient to use. After pressing the 
edges of the wooden frame firmly into the sand on which the 
ripple-mark to be moulded is impressed, plaster of paris is 
sifted through a wire screen until a thickness of one inch or more 
of the plaster has been deposited inside the frame. Ripple- 
mark with deep furrows and angular crests, of course, require a 
thicker deposit of the plaster than the shallow trough type of 
ripple-mark. About one hour is required for the plaster to 
harden under water sufficiently to permit removal. Plaster 
moulds may be made from ripple-mark uncovered at ebb tide 
by using the wooden frame described above. Plaster of paris 
is sifted over the ripple-mark to be moulded inside the frame until 
a layer of the desired thickness has been spread over it. Water 
is then added by sprinkling very gently and uniformly until the 
entire upper surface is uniformly saturated, when it may be 
added more rapidly until the plaster is soaked throughout. 
