410 VEINS MOST FREQUENT IN THE OLDER ROCKS. 



movements, and to convert them into receptacles of metallic 

 ores, accessible by the labom's of man. The greater part 

 of metalliferous veins originated in enormous cracks and 

 crevices, penetrating irregularly and obliquely downwards 

 to an unknown depth, and resembling 4he rents and chasms 

 which are produced by modern Earthquakes. The general 

 disposition of mineral veins wathin these narrow fissures, 

 will be best understood by reference to our first Section. 

 (PI. 1. Figs, k 1. — k 24.) The narrow line which pass 

 obliquely from the lower to the upper portion of this Section, 

 represent the manner in which Rocks of various ages are 

 intersected by fissures, which have become the Receptacles 

 of rich Treasures of Metallic Ore. These fissures are 

 more or less filled with various forms of metalliferous and 

 earthy minerals, deposited in successive, and often corre- 

 sponding layers, on each side of the vein. 



Metalhc Veins are of most frequent occurrence in rocks 

 of the Primary and Transition series, particularly in those 

 lower portions of stratified rocks which are nearest to 

 unstratified crystalline rocks. They are of rare occurrence 

 in Secondary formations, and still more so in Tertiary 

 strata.* 



* M. Dufrenoy has recently shown that the muies of HaBinatite and Spathic 

 iron in the Eastern Pyrenees, which occur in Limestones of three ages, 

 referable severally to the Transition Scries, to the Lias, and to the Chalk, 

 are all situated in parts, where these Limestones are in near contact with 

 the Granite; and he considers that tiiey have all most probably been filled 

 by the sublimation of mineral matter into cavities of the limestones, at, or 

 soon after the time of the Elevation of the Granite of this part of the Pyre- 

 nees. The period of this elevation was posterior to the deposite of the Chalk 

 formation, and anterior to that of the Tertiary Strata. These Limestones 

 have all become crystalline where they are in contact with tlic Granite; and 

 the Iron is in some places mixed with Copper pyrites, and argentiferous 

 galena. (Memoire sur la Position dcs Mines de Fer de la Partie orientale 

 des Pyrenees, 1834.) 



According to the recent observations of Mr. C. Darwin, the Granite 

 of the Cordilleras of Chili (near the Uspcllata Pass) which forms peaks 

 of a height probably of 14,000 feet, has been fluid in the Tertiary period; 



