Another effect of the great lateral thrusts by which the thick sedimentary masses of the geosynclinal were being so violently disturbed, was the production of a great amount of induration and chemical change in these rocks. Masses of soft clay, of the age of that upon which London is built, were by violent pressure reduced to the condition of roofing-slate, similar to that of North Wales. One of the most important discoveries of modern times is that which has resulted in the recognition of the fact of the mutual convertibility of different kinds of energy. We now know that mechanical force may be transformed into heat-force or chemical force; and of such transformations we find abundant illustrations in the crushed and crumpled rock-masses of the Alpine chains. Under the influence of these several kinds of force, not only was extreme consolidation and induration produced among the rock-masses, but chemical affinity and crystalline action had the fullest play among the materials of which they were composed. In many cases we find the originally soft muds, sands, and shell-banks converted into the most highly crystalline rocks, which retain their primary chemical composition, but have entirely lost all their other original features. [Sidenote: FORMATION OF ALPINE GEANTICLINAL.] To the mass of folded, crumpled, and altered strata, formed from a geosynclinal by lateral pressure, geologists have given the name of a 'geanticlinal.' The formation of the Alpine geanticlinal was due to movements which commenced in the Oligocene period, attained their maximum in the Miocene, and appear to have declined and almost altogether died out in the Pliocene period. The movements which resulted in the crushing and crumpling of the thickened mass of sediments along the Alpine line of weakness, also gave rise to the formation of a series of fissures from which volcanic action took place. These fissures were not, however, formed along the original line of weakness, for this had been strengthened and repaired by the deposition of ten-miles' thickness of sediments upon it, but along new fissures opened in directions parallel to the original lines of weakness, and in areas where a much less considerable amount of deposition had taken place since Permian times.