62 STEPHEN TABER 
more branches, but the intersection of veins is extremely rare. 
When numerous they are commonly grouped to form linked-vein 
systems, as in Fig. 1. The vein fibers are usually normal to the 
inclosing walls, occasionally they are oblique, and very rarely they 
are curved or abruptly bent. In some veins most of the fibers 
apparently extend from wall to wall without a break, while in others 
there is a well-defined central parting frequently marked by the 
presence of inclusions of the wall rock. Small vugs are found in a 
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x ON iro 
Mm IT Lore 
LUT Srey ae ap, zs 
Fic. 1.—Veins of fibrous gypsum exposed in walls of quarry near Union Springs 
New York. 
few veins, and these are lined with gypsum crystals of normal 
habit. 
The veins of fibrous calcite are similar to those of fibrous gypsum 
except that ordinarily they are smaller and not so numerous. In 
both gypsum and calcite veins the fibrous structure is as highly 
developed in the larger veins as in those that are smaller, the diam- 
eter of the fibers apparently being independent of the size of the 
veins. However, the diameter of the crystal fibers does vary 
markedly with any change in the texture of the wall rock. In the 
fine-grained limestones and shales the fibers commonly have a 
diameter of 0.05 mm. and less, while in the Onondaga ‘“‘gray lime- 
stone,’’ with its coarsely crystalline texture, the diameters are as 
