X CONTEXTS. CHAPTER XIV. ARE THE PRIMARY SCHISTOSE ROCKS SEDIMENTARY DEPOSITS ALTERED BY THE CONTACT OF IGNEOUS ROCKS ? Passage of primary slates into secondary rocks.—Transitions of two kinds — mineral — and mechanical — the latter no criterion of identity. — The relative position of strata not easily determined—the lias group of the Bdtzberg.—The capability of caloric to alter rocks.— Lyell’s remarks on this subject.— Sir James Hall’s experiments on the fusion of rocks. — The state of rocks next actual lavas—also next trap-rocks—in Skye —in Anglesea—in Ireland.—Dolomization.—Strata next igneous rocks only partially altered. — These changes similar to the effects of caloric. — Condition of primary strata next granite—indicates a transmutation of one earth into another. — The contact of ignited granite and sediment ary deposits disputed. — The arrangement of primary slates incompatible with their being altered deposits. — These slates contain elements not found in sedimentary rocks.— The transfusion of alkalies analogous to that of magnesia in dolomite. — Objections to such transfusions. — The primary slates of Dartmoor—and of the Hartz—said to be altered greywacke.—Those of the Alps, altered oolitic strata.—The association of gneiss and limestone in Jungfrau—of granite and limestone in Glen Tilt and the Pyrenees.—Conclusion - - Page 294 CHAPTER XV. DO THE PRIMARY ROCKS AFFORD PHYSICAL EVIDENCE THAT THEY HAVE EXPERIENCED FISSURES, DISLOCATIONS, AND OTHER MECHANICAL MOVEMENTS ? The apparent indications of displacements.— The curvatures of rocks.— Alternations of curved and straight strata. — Veins often tortuous in straight beds. — The colouring ingredients of rocks arranged in undula ting and contorted lines. — Similar appearances in agates and alabasters —also in igneous rocks.—Sir James Hall’s explanation of curved strata. The moving power imaginary. — The spheroidal structure of rocks.— Primary conglomerates not fragmentary.— The secondary sometimes mechanical—sometimes concretional.— Igneous and aqueous rocks also conglomerated.—Granite-veins — their structure and composition in compatible with theory—analogous to slate-veins — and to certain arrangements in crystalline rocks.— Mineral veins — different kinds of — veins of segregation in Cornwall.—Definition of true veins—objected to. — Intersection of veins — r.o criterion of their relative ages.— Re marks on the heaves and other supposed movements of veins.— Conclusion - - » 333