140 
POPULAR SCIENCE REVIEW. 
Slate caverns ancl sandstone caverns arc different from thos. 
in granite, but the difference chiefly arises from the characteristic 
way in which the rock weathers. Slates present sharp lines, 
jagged edges, and square forms, which are retained in the 
caverns formed within them by the sea. In slate as in granite, 
the wearing away is chiefly from soft veins, and, owing to the 
material, it is not often that the extent is great, or the cavern 
tortuous or complicated. 
Sandstone is rarely so hard and compact as to form a good 
material for caverns, and in its pure state it resists the action of 
Avater so completely that no effects are produced but those 
strictly mechanical. It also rarely contains systematic veins of 
softer material, so that although a sandstone coast-line is often 
extremely tvild, bold, and jagged, it does not often present fine 
caA r erns. There are, however, grand exceptions, as on the 
south coast of Ireland, and elseAvhere. In these cases arched 
rocks are not unfrequent, the sea undermining the stone chiefly 
in the planes of bedding, and entering far into the recesses of 
the rock before the roof falls in, and the cavern becomes a cleft. 
Sandstone caves may be covered Avith limpets and barnacles, but 
are not often rich in the more beautiful varieties of animal life 
and sea- weed. 
Some wonderfully picturesque and grand caves are found 
connected Avith modern lava, and also Avith those ancient lava 
currents called basalt. The great basaltic district of the Giant’s 
Causeway in Ireland, and the coast of the opposite islands of 
Scotland, are penetrated by caverns, which have often been 
described. Fingal’s Cave is one of the best knoAvn in the 
British islands. Similar caves or grottos on a smaller 
scale are known on the banks of the Rhine, not far from 
Bonn; and others, again, in Italy and the various volcanic 
districts of Europe. The sea has had but little to do with 
these : they are dependent partly on the mode in Avhieh the 
columnar masses were originally formed, and partly on the 
kind of decomposition to Avhick they are subjected. 
As a wonderful contrast to these dark fire-developed recesses, 
these gloomy and majestic halls of Pluto, we may just allude 
to the brilliantly-lighted ice caverns, frequently formed in 
glaciers, though not often A T i si table by man. Nothing can be 
conceived more beautiful than the colour transmitted through 
ice, and nowhere can this be seen in perfection but in one 
of these caverns. The river of cold water that has formed the 
cavern rushes along at one’s feet — the only disturbance to the 
dead stillness that otherAvise prevails. Here is no life, no mark 
of life to be traced ; but there is occasionally a floor of broken 
fragments of rock, torn away by the action of the cold that has 
originated the glacier in the thin air of the mountain-top. 
