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ON THE VOLCANIC PHENOMENA OF YVESUVIUS. 401 
nothing more than the loose surface fragments of the limestone slopes 
above. Their occurrence near the bottom of the tuff is just what we 
should expect to find under those conditions. The limestone surface 
é, Vegetable soil, Vesuvian dust and lapilli, &c., variable ; g, pipernoid tuff with 
a band of fluoriferised limestone fragments near the bottom, which is in- 
clined, and the larger inclusions are nearer the lower part of the slope, 15 to 
30m. ; f, pumiceous sand redder and more argillaceous at the top, 0°30 m. ; 
é, black carbonaceous earth with a few fragments of white pumice. This 
bed thins out to nothing at the lower end of section, 0:40 m.; d, ochreous 
earth with white pumice, 0°65 m.; c, white pumice, browner and dustier at 
the top, 0°85 m.; 4, yellowish or reddish brown earth variable from 0°50 to 
2:00 m. ; a, limestone rounded and rilled, and with gaping clefts, as if ex- 
posed to action of acids. The surtace gives a fluorine reaction, and is spongy 
to some depth. 
beneath the section is also of great interest. It is furrowed and rounded 
as if a stream of acid water had flowed over it, and much resembles a 
white marble sink of a laboratory etched out and furrowed by the acid 
liquids flowing over it. A similar condition can often be seen on the 
Neapolitan water-sellers’ marble counters in Naples from the action of the 
waste lemon-juice. The old cracks of the limestone are open and gaping, 
whilst the surface is rotten and porous from 1 to 5cm. more in depth, 
and the thin crust affords a marked fluorine reaction. All these cha- 
racters point to the fact that this limestone has been exposed to chemical 
corrosion not of a usual kind, and that one of the corrodents was a com- 
a9 fluorine. But, as may be seen by the section, this fluoriferous 
; DD 
