212 DILUVIAL BOULDERS IN ITALY AND SWITZERLAND. 
mulations of sand and gravel (which he calls “ terrains de transport 
anciens,” as compared with the postdiluvian detritus of the floods of 
modern rivers), reposing on the regular strata of that steep and 
almost insulated mountain. These blocks can only have arrived 
at their present place by being drifted from some part of the distant 
Alpine chain that encircles the upper extremity of the valley of 
the Po. 
De Saussure has recorded a valuable series of observations on the 
effects of what he calls the debacle, or breaking up and transport 
of massive rocks and gravel, by an enormous rush of waters, in 
Switzerland. The most remarkable of these is the transport of 
blocks of granite from Mont Blanc* to the Jura Mountains, across 
the space which is now the Lake and Valley of Geneva. These 
effects appear to be only a larger example of that same diluvial 
action which we have been tracing in other countries; and which 
has operated in Switzerland on a scale proportionate to the mag¬ 
nitude of the Alpine masses on which it had to exert itself. For 
the detail of these effects, I must refer to Saussure’s own descriptions, 
and to Sir James Hall’s excellent paper in the Edinburgh Philo¬ 
sophical Transactions, before quoted; in which he offers some very 
ingenious and not improbable conjectures, as to the manner in 
* These blocks lie on the Jura Mountains, at an elevation of 2000 feet above the 
Lake of Geneva. Their size in some cases amounts, as in the Valley of Monetier, upon 
the Saleve Mountain, to 1200 cubic feet; and in the case of those on the Coteau de 
Boissy to 2250, and even to 10,296 cubic feet, which is the measure of the block called 
Pierre a Martin. 
