46 
ELEMENTS OF GEOLOGY. 
In the locality now under consideration, situated a few 
miles to the west of Nice, there are many geological data, 
the details of which can not be given in this place, all lead¬ 
ing to the opinion that, when the deposit of the Magnan was 
formed, the shape and outline of the Alpine declivities and 
the shore greatly resembled what we now behold at many 
points in the neighborhood. That the beds a, 5, c, d are of 
comparatively modern date is proved by this fact, that in 
seams of loamy marl intervening between the pebbly beds 
are fossil shells, half of which belong to species now living 
in the Mediterranean. 
Ripple-mark.-^The ripple-mark, so common on the surface 
of sandstones of all ages (see Fig. 8), and which is so often 
seen on the sea-shore at low tide, seems to originate in the 
drifting of materials along the bottom of the water, in a 
manner very similar to that which may explain the inclined 
layers above described. This ripple is not entirely confined 
to the beach between high and low water mark, but is also 
produced on sands which are constantly covered by water. 
Similar undulating ridges and furrows may also be some¬ 
times seen on the surface of drift snow and blown sand. 
The ripple-mark is usually an indication of a sea-beach, or 
of water from six to ten feet deep, for the agitation caused 
by waves even during storms extends to a very slight depth. 
To this rule, however, there are some exceptions, and recent 
ripple-marks have been observed at the depth of 60 or 70 
feet. It has also been ascertained that currents or large 
bodies of water in motion may disturb mud and sand at the 
depth of 300 or even 450 feet.* Beach ripple, however, may 
usually be distinguished from current ripple by frequent 
changes in its direction. In a slab of sandstone, not more 
than an inch thick, the furrows or ridges of an ancient ripple 
may often be seen in several successive laminae to run to¬ 
wards different points of the compass. 
* Darwin, Vole. Islands, p. 134. 
