Vlll CONTENTS. contemporaneous and true veins—but are identical, only differing in size.—Large quartz-veins intersecting both the granite and slate,— at St. Michael’s Mount,—at Mousehole,—and at Cape Cornwall.— The connection between metalliferous veins and the containing rocks.— Veins curved both in then - course and underlie,—as at Polgooth and Huel Jewel mines. — Veins intersect each other both in their length and depth, accompanied by apparent movements,—as at Dolcoath, Weeth, Ting Tang, Huel Friendship, South Huel Towan, and Huel Peever mines. — Interference of veins and elvan-courses,—as at Polgooth and Dolcoath mines. — Veins similarly affected without the intervention of veins of any description, as at Balnoon and Ding Dong mines Page 163 CHAPTER X. GENERAL REMARKS ON THE PRIMARY ROCKS. Recapitulation of the principal facts detailed in the preceding chapters.— Composition of the granitic rocks. — Each granitic formation characte rised by peculiar series of granite, dependent on the nature of the accessory mineral. — This mineral subject to transitions, accompanied by corresponding changes in the series. — The different kinds of granitic rocks variously associated together — their disposition among the primary schists—the nature of this connection. — Masses of granite, whether large or small,—insulated or interstratified with slates,—are not of a 'different nature. — General remarks on the primary schists — their composition, — modes of union, — and frequent passage into each other. — No fixed order of succession. — Their nature illustrated by a series commencing with micaceous gneiss. — The strata of each member of the schistose group composed of slates and compact varieties — the latter pass into granitic rocks. — This group, in each primary district, charac terised by same minerals as the adjacent granite. — Remarks on the apparent fragmentary composition of some primary rocks,—and on the analogy between rock and mineral veins. - - - 193 CHAPTER XI. A SKETCH OF THE PREVAILING THEORY CONCERNING THE NATURE OF THE PRIMARY ROCKS. Two classes of the primary rocks, the stratified and unstratified — the former of aqueous, the latter of igneous origin. — The whole earth ori ginally igneous— the granitic rocks the result of its secular refrigeration. —Igneous rocks of three kinds—granitic, trappean, and volcanic.— Gran ite a rock of all ages. — The crystalline strata associated with granite also belong to various epochs — supposed to be altered or metamorphic rocks. —The determination of the precise age of an individual mass of granite.— De Beaumont’s theory concerning the relative ages of mountain-chains — not generally received. — Granite protruded in a solid as well as a fluid state. — The prevailing theory a modification of that of Hutton —