115 
Museum Bulletin No. 25. 
Plate XXX. 
A. Interference ripple-mark on Coal Measure sandstone, Cape Breton, 
N.S, (Page 43.) 
B. Interference ripple-mark on Berea sandstone, Elyria, Ohio. Photograph 
by G. K. Gilbert, U.S.G.S. (Pages 36, 43.) 
