CAUSES OF DIAGONAL STRATIFICATION. 45 
descend from the Alpine declivities to the shore, bring down 
annually, when the snow melts, vast quantities of shingle and 
sand, and then, as they subside, fine mud, while in summer 
they are nearly or entirely dry; so that it may be safely as¬ 
sumed that deposits like those of the valley of the Magnan, 
consisting of coarse gravel alternating with fine sediment, 
are still in progress at many points, as, for instance, at the 
mouth of the Var. They must advance upon the Mediter¬ 
ranean in the form of great shoals terminating in a steep 
talus; such being the original mode of accumulation of all 
coarse materials conveyed into deep water, especially where 
they are composed in great part of pebbles, which can not 
be transjDorted to indefinite distances by currents of mode¬ 
rate velocity. By inattention to facts and inferences of this 
kind, a very exaggerated estimate has sometimes been made 
of the supposed depth of the ancient ocean. There can be 
no doubt, for example, that the strata a. Fig. 7, or those near¬ 
est to Monte Calvo, are older than those indicated by 5, and 
these again w^ere formed before e ; but the vertical depth of 
gravel and sand in any one place can not be proved to 
amount even to 1000 feet, although it may perhaps be much 
greater, yet probably never exceeding at any point 3000 or 
4000 feet. But were we to assume that all the strata were 
Fig. 8. 
Slab of ripple-marked (New Red) sandstone from Cheshire. 
once horizontal, and that their present dip or inclination was 
due to subsequent movements, we should then be forced to 
conclude that a sea several miles deep had been filled up 
with alternate layers of mud and pebbles thrown down one 
upon another. 
