1G8 
OLDER PLIOCENE PERIOD. 
[Ch. XII. 
precipices are laid open on each side, varying from 200 to 600 
feet in height, and composed of inclined beds of shingle, some- 
times separated by layers of sand, and more rarely by blue 
micaceous marl. The pebbles in these stratified shingles agree 
in composition with those now brought down from the Alps by 
the Var and other rivers on this coast. 
The dip of the strata is remarkably uniform, being always 
southwards, or towards the Mediterranean, at an angle of 
about 25°. In summer, when the bed of the river is dried up, 
the geologist has a good opportunity of examining a section of 
the sti'ata, as the channel crosses for many miles the line of 
bearing of the beds, which may be traced to the base of Monte 
Calvo, a distance of about nine miles in a straight line from 
the Mediterranean *. It is usually impossible to determine 
the exact age of such accumulations of sand and gravel, in con- 
sequence of the total. absence of organic remains. Their non- 
existence may depend chiefly on the disturbed state of the 
waters, where great beds of shingle are formed, which are 
known to prevent testacea and fishes from living in Alpine tor- 
rents, partly on the destruction of shells by the same friction 
which rounded the pebbles, and partly on the permeability of 
the matrix to water, which may carry away the elements of the 
decomposing fossil body, and substitute no others in their place 
which might retain a cast of their form. 
But it fortunately happens, in this instance, that in some 
few seams of loamy marl, intervening between the pebble-beds, 
and near the middle of the section, shells have been preserved in 
a very perfect state of preservation, and these may furnish a 
zoological date to the whole mass. The principal of these 
interstratified masses of loam occurs near the church of St. 
Madeleine (at c, diagram No. 29), where the active researches 
of M. Risso have brought to light a great number of shells 
which agree perfectly with the species found in much greater 
abundance at a spot called La Trinity and some other locali- 
* I examined this section in company with Mr. Murchison in 1828. 
