VAN 



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V E I 



valve to open in one direction only 

 for the passage of fluids, and pre- 

 vents their retrograde motion, or 

 regurgitation. Thus there are 

 valves in the heart ; valves in the 

 veins; valves in the lympha- 

 tics, &c. 



VA^A'DIUM. A metal discovered by 

 Sefstrom, in Sweden, and thus 

 named after Vanadis, a Scandina- 

 vian deity. Its properties are not 

 yet known. 



VA'BIEGATED SAND'STONE. The New 

 Ked Sandstone of the English ; the 

 Gres Bigarre of the French, and 

 the Bunter Sandstein of the German 

 geologists. For a description see 

 New Red Sandstone. 



VAEI'ETY. (varietas, Lat.) A sub- 

 division of species, arising from 

 accidental, or unimportant and 

 trifling, differences. 



VAEI'OLITE. (from variolw, Lat.) The 

 name given to an amygdaloidal or 

 porphyritic rock, merely in conse- 

 quence of its spotted appearance. 



VA'SCULAE. (from vasculum t Lat. a 

 little vessel.) Containing vessels 

 or tubes ; full of vessels within 

 which the fluids are confined, and 

 by which their course and their 

 velocity are regulated. 



VEGETABLES. The first appearance of 

 vegetable existence may be discov- 

 ered in the transition slate, which 

 contains impressions of algse or 

 sea- weeds. A few fronds of ferns 

 have been found in some of the 

 transition rocks. "It appears," 

 says Buckland, " that nearly at the 

 same points in the progress of 

 stratification, where the most stri- 

 king changes take place in the 

 remains of animal life, there are 

 found also concurrent changes in 

 the character of fossil vegetables." 



VEIN, (vena, Lat.) 



1. In anatomy, elastic tubes perva- 

 ding every part of the body, and 

 conveying dark or venous blood 

 from the arteries to the heart. 

 The veins are larger and more 



numerous than the arteries, and 

 may be compared to rivers, which, 

 collecting all the water that is not 

 imbibed by the soil, and reconvey- 

 ing it into its general receptacle, 

 the ocean, perform an analogous 

 office in the economy of nature. 

 2. In geology and mineralogy, 

 fissures in rocks filled up by 

 mineral or metallic substances dif- 

 fering from the rocks in which 

 they are situated. Mineral reposi- 

 tories of a flat or a tabular shape, 

 which in general traverse the 

 strata of mountains, crossing the 

 strata, and having a different di- 

 rection from them, and filled with 

 mineral matter, differing from the 

 nature of the rocks in which they 

 occur. Bakewell says, " perhaps 

 the reader may obtain a clearer 

 notion of a metallic vein, by first 

 imagining a crack or fissure in the 

 earth a foot or more in width, and 

 extending east and west on the 

 surface, many hundred yards. 

 Suppose the crack or fissure to 

 descend to an unknown depth, not 

 in a perpendicular direction, but 

 sloping a little to the north or 

 south. Now, let us again suppose 

 each side of the fissure to become 

 coated with mineral matter of a 

 different kind from the rocks of 

 which the fissure is made, and then 

 the whole fissure to be filled by 

 successive layers of various me- 

 tallic and mineral substances ; we 

 shall thus have a type of a metallic 

 vein. Its course from east to west 

 is called its direction, and the dip 

 from the perpendicular line of 

 descent its hading. Thus it is said 

 to hade or dip to the north or 

 south." 



Veins occur principally in the 

 primary and transition rocks, but 

 they are also found in the lowest 

 of the secondary series. 



As regards the geographical dis- 

 tribution of mineral veins, it is an 

 established fact, that while exten- 



