48 
MUSEUM BULLETIN NO. 25. 
been formed while the beds were being deposited. It is probable 
that these large ripple-marks were more subject to destruction 
by erosion than the smaller ones, while later deposits of sand 
were being laid down, or less capable owing to size of being 
fully uncovered when preserved without partial destruction. 
RIPPLE-MARK AS A CRITERION OF MARINE OR LACUSTRINE SEDI- 
MENT. 
Since the symmetrical and asymmetrical types of ripple-mark 
are the product respectively of wave and current action, it is 
possible to infer from the absence or rarity of one or the other 
type of ripple-mark in a given series of rippled beds whether they 
were accumulated under the dominant influence of current or 
wave action. Current action is nearly everywhere a feature of 
shallow marine waters, owing to the tides, and it is generally 
absent or comparatively rare in lakes. Hence the abundance of 
the wave-made type of ripple-mark in a sandstone formation 
(Plates XXV, XXVI) and the absence of the asymmetrical type 
would indicate its formation under lacustrine conditions. The 
great predominance on the other hand of the asymmetrical 
type (Plates XXVII, XXIX) of ripple-mark would as certainly 
suggest the work of tidal current action and marine condi- 
tions. Wave action is, of course, as much a feature of marine 
as it is of lake waters; but, as has been pointed out in the first 
part of this paper, the product of the joint action of wave and 
current on sand is invariably the asymmetric ripple, while the 
entire absence of current action is essential to the formation of the 
symmetrical ripple. 
The Joggins section well illustrates this interpretation of the 
significance of types of ripple-mark. The Carboniferous section 
at Joggins, Nova Scotia, was carefully examined with reference 
to the type of ripple-mark developed in it. The general absence 
from this section of marine fossils and the marvellous abundance 
at many horizons of upright tree trunks often holding terrestrial 
fossils and other land plants can leave no doubt that the sediments 
in it, with the possible exception of some interpolated marine 
beds, are of non-marine origin and represent the deposits of a 
shallow marshy lake probably near and at times connected 
