THE CAVERNS. 
137 
powerful as they might be, would here have little effect. They 
must beat against this granite in vain. Except here and there, 
where a soft vein occurs, the rock is all hard. There is no 
mixture of modern water-deposited limestone or sandstone — 
no beds of yielding clay and treacherous sand — no loose rocks 
or decomposable material. All is granite, or hornstone, or 
porphyry, or some of those other rocks recognized by 
geologists as among the most indestructible. But what is the 
fact ? Of all places within easy access there is none like Sark 
for caverns — nowhere is the history of the origin and enlarge- 
ment of one great class of caverns more manifest — nowhere is 
granite more clearly the slave of water, performing all its 
behests, helping to subjugate completely the very class of rocks 
to which it belongs, the broken rocks themselves working in- 
cessantly and actively with the waves, helping to tear into 
shreds and carry away as mud and sand all that is hardest and 
most durable. 
Caverns in granite are generally water-worn from without, 
or, in other words, the mechanical force of the waves is greater 
than the dissolving and chemical action of fresh water perco- 
lating the rocks. Always, no doubt, a solvent, the effect of 
water in this respect on rocks which contain but little alkaline 
earths is comparatively small ; but, on the other hand, such 
rocks, having been originally formed at high temperature and 
cooled down, have cracked, and the cracks have become filled 
with various mineral substances, often decomposing more or less 
readily than the rock. It is not difficult to understand that the 
effect of this difference of condition must involve a partial and 
irregular destruction of the rock. The softer part being- 
removed, the harder part falls down, and thus we have those 
never-ceasing little bays, creeks, and inlets, those wonderful 
rocs and fiords, and other variously named irregularities of the 
coast-line, which greatly contribute to the wildness and 
grandeur of granite coast scenery. 
And thus also we have caverns formed. On that part of a 
group of hard rocks that is softer than the rest, the water first 
acts. It beats vehemently against the rock with a force some- 
times of many pounds on the square inch. On an exposed 
coast blocks of stone weighing two or three tons, and pre- 
senting more than eight or ten square feet of surface, are 
lifted up and carried over obstacles to a great distance. 
Smaller stones are rolled about -and hammered against each 
other, and against every weak place in the cliff. After a time, 
the weak place is hollowed out, and an open cave is the result. 
Two or three veins, parallel to each other, are acted on in this 
way, perhaps at the same time, and an entry is made. The 
commencement of a tunnel is driven, a tunnel that shall connect 
