NEWER PLIOCENE VOLCANIC ROCKS. 
529 
tion has disclosed, in one spot, a wall of columnar basalt 
about fifty feet high."^ 
The excavation of the ravine is still in progress, every 
winter some columns of basalt being undermined and car- 
ried down the channel of the river, and in the course of a 
few miles rolled to sand and pebbles. Meanwhile the cone 
of Come remains unimpaired, its loose materials being pro¬ 
tected by a dense vegetation, and the hill standing on a 
ridge not commanded by any higher ground, so that no 
floods of rain-water can descend upon it. There is no end 
to the waste which the hard basalt may undergo in future, if 
the physical geograiDhy of the country continue unchanged— 
no limit to the number of years during which the heap of in¬ 
coherent and transportable materials called the Puy de Come 
may remain in an almost stationary condition. 
Ptty de Parioit ,—The brim of the crater of the Puy de 
Pariou, near Clermont, is so sharp, and has been so little 
blunted by time, that it scarcely affords room to stand upon. 
This and other cones in an equally remarkable state of in¬ 
tegrity have stood, I conceive, uninjured, not in spite of their 
loose porous nature, as might at first be naturally supposed, 
but in consequence of it. No rills can collect where all the 
rain is instantly absorbed by the sand and scoriae, as is re¬ 
markably the case on Etna; and nothing but a water-spout 
breaking directly upon the Puy de Pariou could carry away 
a portion of the hill, so long as it is not rent or ingulfed by 
earthquakes. 
Newer Pliocene Volcanic Rocks. —The more ancient por¬ 
tion of Vesuvius and Etna originated at the close of the 
Newer Pliocene period, when less than ten, sometimes only 
one, in a hundred of the shells differed from those now liv¬ 
ing. In the case of Etna, it was before stated (p. 204) that 
Post-pliocene formations occur in the neighborhood of Cata¬ 
nia, while the oldest lavas of the great volcano are Pliocene. 
These last are seen associated with sedimentary deposits at 
Trezza and other places on the southern and eastern flanks 
of the great cone (see above, p. 205). 
Cyclopean Islands ,—The Cyclopean Islands, called by the 
Sicilians Dei Faraglioni, in the sea-cliffs of which these beds 
of clay, tuff, and associated lava are laid open to view, are 
situated in the Bay of Trezza, and may be regarded as 
the extremity of a promontory severed from the main land. 
Here numerous proofs are seen of submarine eruptions, by 
which the argillaceous and sandy strata were invaded and 
cut through, and tufaceous breccias formed. Inclosed in 
* Scrope’s Central France, p. 60, and plate. 
23 
