202 
POPULAR SCIENCE REVIEW. 
and to tlie geologist there is no lesson more valuable and 
suggestive than this history of metamorphosis, with illustra- 
tions ready at hand. 
The first thing that strikes the eye on mounting the cone 
and reaching the edge of a volcanic crater, either at the time 
or recently active, is the intensity of the colours exhibited in 
long streaks, which sometimes concentrate into broad bands. 
These colours include every variety of yellow, passing into the 
purest white on one side and into deep orange or brown on the 
other ; occasionally, but more rarely, the colours include ver- 
milion and other reds. The brilliancy is such that no pencil 
could imitate it, and the appearance can only be compared to 
the hues of the clouds during an autumn sunset in a warm 
climate. On a near approach, these fines of colour are found 
to mark accurately fines of crack or fissure in the soft mass of 
the cone, through which fumaroles are passing. One is at first 
inclined to believe that as sulphur seems so natural a companion 
to all volcanic phenomena, we have before us an unexplored 
mine of this mineral, and one wonders that any hesitation 
should be felt in making use of it. But there is perhaps hardly 
a specimen of native sulphur, whether crystalline or efflores- 
cent, to be found. All these bright colours are evanescent, 
and we must be contented to admire them where they are. 
They are liable to be washed away by the first shower, though 
in that case they re-appear immediately. They would lose 
their beauty if exposed to ordinary air at ordinary tempera- 
tures. They are almost entirely deliquescent salts of ammonia, 
soda, and iron. They are also constantly changing their form 
and nature, and they seem to mark in some measure the par- 
ticular chapter of the history of the eruption which lies open 
before us. 
No one who comes into a volcanic country and looks at the 
objects before him with any attention will fail to see that he 
has an opportunity here of seeing something of Nature's 
chemical methods, just as in a country where there are glaciers 
or an exposed sea-coast, he may study the mechanical methods 
adopted to produce and modify rocks. A volcanic cone begins 
by being a mere heap of scoriaceous matter erupted and heaped 
round some part of a crevice or fissure opening from a con- 
siderable depth in the earth, and partly filled with melted rock. 
The cone is constantly becoming higher and higher as the 
eruption proceeds. It is hollow and funnel-shaped inside, 
communicating with the interior of the earth as long as the 
eruption lasts. Occasionally melted rock rises in it through 
this central funnel-shaped hole, and sometimes a flood of this 
melted rock issues from the top or side. In this case the re- 
mainder of the eruption takes place through hot and fractured 
