531 
Quartz Rock of the Lie key Hilly &c. 
in June, 1818, in the valley of the Dranse in Switzerland), and the 
daily action of torrents and rapid rivers in times of flood, is com- 
petent to produce partially over a limited district beds of gravel 
somewhat similar to those of the great diluvian waters ; striking 
examples of this kind are afforded in the Duchy of Venice, along 
the base of that part of the Alps which lies immediately on the 
north and north-west of the town of Valvasone, where the flood 
waters of the Tagliamento, the Meduna, and the Zelline, have 
strewed the plains to an extent of many miles from the base of the 
mountains with a beach of pebbles of enormous breadth, which in 
summer is dry and barren, resembling a naked Chesil bank on the 
sea shore. Similar features are presented by the Torre and Malina 
torrents on the north-east of Udina, and by the numerous torrents 
that descend into the plain of Lombardy from the mountains on the 
north of Verona and Vicenza. The Trebbia and Taro rivers also, 
and all the torrents adjacent to them, which fall into the Po from 
the south, near Parma and Piacenza, cover the lands in the vicinity 
of their courses with a similar and annually increasing accumulation 
of detritus, from that part of the Apennines in which they take 
their origin. And in our own country, the small river of Avon 
Lwyd or Tor Vaen, which descends from the west side of the 
Blorenge mountain in Monmouthshire, by the valley of Pontypool, 
presents, at the point where it leaves the mountains immediately 
below that town, a naked strand of pebbles, that is perpetually 
shifting and laying desolate the level regions that succeed imme- 
diately to the sudden termination of the steep and precipitous 
mountain valley, along which the torrent has its course above 
Pontypool. 
At the point where transverse mountain vallies fall into the great 
ongitudinal vallies, we sometimes find a considerable talus-shaped 
