As this cave is at the foot of Ingleborough, a cold wind, 24° below the temperature of the external air, which issued from the mouth of it, might very well be supposed to come from the inmost recesses of that mountain. Ingleborough, which consists entirely of strata of limestone and grit, nearly horizontal, and alternating with one another, rises to the height of 1800 or 2000 feet above the spot where we now stood. This, I believe, is the greatest thickness of secondary strata that has ever been observed incumbent on the primary, and it is therefore a geological fact highly deserving of attention. The country all round, to a very great extent, is composed of limestone, with a few beds of grit interposed, and forming, beside Ingleborough, some other high mountains, such as Wharnside and Pennigant, all resting, it is probable, on the same foundation. At the spot just described, no breccia appeared to be interposed between the primitive and secondary rock; but we found a breccia at another point of the same junction, not far distant. This was at a cascade, in the river Greta, called Thornton Force, about two miles and a half from the place just mentioned. The Greta here precipitates itself from a horizontal rock of limestone; and, after a fall of about eighteen or twenty feet, is received into a bason which it has worked out in the primary schistus. This schistus is in beds almost perpendicular; it exactly resembles that which has Just been described, and stretches nearly in the same direction. On the south side of the river a breccia was seen, lying upon the schistus, or rather, it might be said, that the lowest beds of limestone contained in them many rounded fragments of stone, which, on comparison, resembled exactly the schistus underneath. The primary rock itself is here seven or eight hundred feet above the level of the sea. The same schistus, somewhat lower down the valley, and nearer to Ingleton, appears in large quantities, and is quarried for slate. Here, however, the immediate junction of the limestone and schistus does not appear. I have dwelt longer on the description of these appearances than on any others of the same kind, because, from the great mass of secondary strata which here covers the primary, the circumstances are such as we cannot expect to see very often exemplified. 198. The Lakes of Cumberland are much visited by travellers; and it may be worth remarking, on that account, that, as the site of these lakes is a patch of primary country, bounded on all sides by secondary, so, in the rivers that run from the lakes, such junctions as we are now treating of may be expected to be found. Under Dun-Mallet, on the side toward Ulles Water, we observed a breccia, which was in horizontal layers, and seemed to lie on the primary schistus, so that the whole hill is perhaps a piece of more indurated breccia, or secondary rock, which has resisted the wearing and washing down of the rivers better than the rest.