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 their 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 el van-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 XL 



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 



