But in the case of less fluid lavas, such as those of intermediate or acid composition, for example, the effect would be far otherwise. Such lavas, not flowing readily from the centre of eruption, would tend to form great bulky lenticular masses between the strata which they forced asunder, and, in so doing, could not fail to upheave and fissure the great mountain-mass above. Vast lenticular masses of trachytic rock, thus evidently forced between strata, have been described by Mr. G. K. Gilbert, as occurring in the Henry Mountains of Southern Utah, and by him have been denominated 'laccolites,' or stone-cisterns. Whether the great basaltic sheets, like those described by Macculloch, and those more bulky lenticular reservoirs of rock of which Mr. Gilbert has given us such an admirable account, were in all cases connected with the surface, may well be a matter for doubt. It is quite possible that, in some cases, liquefied masses of rocky materials in seeking to force their way to the surface only succeeded in thus finding a way for themselves between the strata, and their energy was expended before the surface was reached and explosive action took place. But it is an undoubted fact that beneath many of the old volcanoes, of which the internal structure is now revealed to us by the action of denuding forces, great intrusive sheets and laccolites abound; and we cannot doubt that beneath volcanoes now in a state of eruption, or in those which have but recently become extinct, similar structures must be in course of formation. [Sidenote: EFFECTS OF INTRUSION BENEATH CONES.] That great upheaving forces have operated on volcanoes, subsequently to the accumulation of their materials, we have sufficient evidence in the Val del Bove of Etna, the Caldera of Palma, the Corral of Madeira, &c. In all of these cases we find a radial fissure ('barranco') leading into a great crateral hollow; and these radial fissures are of such width and depth that their origin can only be referred to a disruptive force like that which would be exercised by the intrusion of masses of more or less imperfectly fluid material between the subjacent strata. These facts, of course, lend no countenance to the views formerly held by many geologists, both in Germany and France, that the materials of which volcanoes are built up were deposited in an approximately horizontal position, and were subsequently blown up like a gigantic bubble. In Etna, Palma, and Madeira we find abundant proofs that the mass existed as a great volcanic cone before the production of the fissures (barrancos), which we have referred to the force exercised during the intrusion of great igneous masses beneath them.