RECENT AND FOSSIL RIPPLE-MARK. 
19 
ripple-mark on the other hand displays an enormous amount of 
variation in amplitude (Figure 3). This variation of the ampli- 
tude appears to depend chiefly on the load of sediment carried 
and on the velocity of the current. The estuaries of the bay of 
Fundy afford ample opportunities for studying this variable 
feature of current ripple-mark. The tidal currents of the bay 
of Fundy furnish a large variety of the conditions influencing 
ripple-mark formation. The great range of the tides in the 
bay, amounting to more than 40 feet at some points (see Plate 
VI), results in currents of unusual power in the estuaries of the 
rivers entering this bay. In some of these streams the turn of 
the tide is accompanied by the phenomenon known as the bore. 
The advancing tide ascends the river channel in the form of an 
abrupt steep faced wave 1 to 3 feet high, or as a succession of 
waves. Both of these phases of the bore are shown on Plate 
V. Under the influence of the powerful tidal currents heavily 
loaded with silt, a mammoth type of ripple-mark is developed in 
many estuaries of the bay of Fundy. The ripple-mark which is 
most commonly seen along the sea shore and which at most 
localities is the only kind seen has the ridges spaced at intervals 
of about 3 inches. This familiar form of ripple-mark is shown on 
Plate VII. A graded series of these forms can be selected showing 
ridges varying from a few inches to several feet apart (see Figure 
3). The mouth of a stream entering St. Mary bay at the 
northwest corner just above the bridge affords some striking 
examples of a large type of ripple-mark produced by the very 
strong current of the stream at ebb tide. These are remarkable 
for their large amplitude, the crests being 2 to 4 feet apart and the 
trough 3 to 6 inches deep (see Plate VIII A). Their large size 
and nearly flat upstream sides give them a terrace-like appear- 
ance. They have less perfect parallelism than ordinary ripples 
but are, nevertheless, parallel in a general way. In this ripple- 
mark the lee slopes are inclined at angles of from 25 to 32 degrees 
and the upstream slopes at | to 5 degrees. The profile of an 
example which was measured is shown in Figure 3 G. The 
slope of the upstream side is often very irregular and may be 
trough-like just in front of the steep sloping face. 
