4 
MUSEUM BULLETIN NO. 25. 
separated by a sharply defined contact line; in such a case 
ripple-mark if present on the sand will stop abruptly at the 
mud contact line. I have observed striking examples of this 
truncation of ripple-mark pattern by mud beds along the St. 
Lawrence river. The limitation, of ripple-mark to granular 
sediments affords an important clue to the original texture of 
ripple-marked limestones. 
The universality of this phenomenon on the sands of dune 
and desert regions and on the sandy beds of seas, lakes, and rivers,, 
gives to it a degree of importance hardly suggested by the brief 
treatment usually accorded to it in textbooks. Ripple-mark, 
as observed by Sir J. D. Hooker , 1 has sometimes been mistaken 
for the fluting of Sigillaria stems and has led to the grave error 
of determining as Coal Measures beds far removed from this 
horizon. 
A record of the work of air and water currents has been 
inscribed in terms of ripple-mark on some of the oldest of the 
sedimentary rocks. Even before marine life began to record its 
history with fossil remains, ripple-mark was being formed which 
has persisted in a good state of preservation to the present time. 
In many later formations where fossils are rare or unknown 
ripple-mark is often most beautifully preserved. Thus it happens 
that where the palaeontological record fails much may be gleaned 
from a study of ripple-mark concerning the history of older sedi- 
ments. Fossil ripple-mark should indicate whether the material 
impressed by it was laid down under wave or current action, 
and if currents were present their direction and within certain 
limits their velocity. Where both fossils and ripple-mark are 
preserved in the same beds the correct interpretation of the 
latter may aid greatly in understanding the environmental 
conditions of the former. It is evident that any trustworthy 
interpretation of the significance of fossil ripple-marks must rest 
upon a detailed study of the conditions under which they are 
now being formed. The first part of this paper will, therefore, 
undertake to indicate the conditions under which the several 
types of ripple-mark are formed. With reference to their 
^Himalayan Journals, pp. 31 and 41, 1891, 
