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The origin of the caves and fissures is obscure, yet the following facts seem to favour the opinion that they owe their formation partly to disturbing movements, and partly to the solvent power of water.

It is a remarkable and general fact, that the ossiferous caves and fissures are situated almost exclusively in limestone, not only in England, but in France, Belgium, Westphalia, Franconia, Wurtemburg, along the Mediterranean coasts, in North America, in Australia. This is, however, not at all peculiar to ossiferous caves, for it is a rare thing to meet with considerable cavities underground in any other rock than limestone.

It does not appear that these cavities are specially abundant in districts where subterranean movements have been most powerful or numerous; hardly one cave in the North of England can thus be accounted for; but it is certain that, in two districts of the same calcareous formation, caves may abound in the thick and massive rocks, but be unknown in those where thinner layers are associated with sandstones and shales. This is remarkably the case with the carboniferous limestone of Yorkshire and Derbyshire: where several hundred feet of "Scar" limestone exist in one thick mass, caves abound, as at Matlock, Castleton, Buxton, Yorda's Cave, Wethercote Cave near Ingleton, Gowden Pot Hole in Nidderdale, Dunald Mill Hole near Lancaster, &c.—but not a single cave is known among the thinner and more varied "Yoredale Rocks."

Kirkdale Cave is in a very thick part of the coralline oolite, and calcareous grit; the Franconian and other German caves are also in thick rocks of limestone.

It appears remarkable, that so large a proportion of the known caves are situated near, and open on the sides of, existing valleys, though often much above their actual level; along some vast bodies of water are now running, and daily enlarging the passage (Peak Cavern, great cavern in Nidderdale); and from the mud mixed with the bones in even the driest repositories, from the decomposition and wearing of the surface of the bones, the stalagmitic