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University of California Publications in Geology [Vol. 11 



may occur near igneous contacts, but these are more irregular in 

 thickness and have an entirely different arrangement. In hand speci- 

 mens it is generally impossible to see any evidence of displacement 

 along these veins, but in thin section slight displacements are visible. 

 One vein may offset another, or a radiolarian may be cut in two and 

 the two parts displaced by a small amount. The quartz of the veins is 

 granular and the grains are much coarser than the grains of the chal- 

 cedonie matrix of the rock. The same is true when the veins are filled 

 with chalcedony. 



LEACHING OF THE EED CHEETS 



In many cases the quartz veins run through the cherts with no 

 appearance of any alteration of the walls by circulating waters. In 

 a few instances there is evidence of the leaching of the walls of the 

 vein and the abstraction of iron oxide. In other cases, where there are 

 mi quartz veins, the rock is seen to be traversed by a network of 

 irregular white or pale greenish streaks, extending transversely across 

 the beds, and contrasting strongly with the deep red color of the un- 

 affected chert (plate 31a). On examining these streaks they are 

 found to mark a zone of leaching and discoloration along some fissure 

 through the chert. In places the process has gone so far that a large 

 proportion of the chert is greenish with little cores and residual patches 

 oi red chert within the network of fissures. In a few instances red 

 shales have been seen interbedded with greenish cherts which show 

 residual patches of red coloration, evidently indicating that the more 

 easily fissured cherts had permitted freer circulation of waters than 

 the shales. 



In many places the upper and lower surfaces of the beds of red 

 chert may show irregular networks of white streaks. These lines of 

 decoloration are confined to the surface layer of the chert beds and 

 appear to be due to the circulation of waters along the contacts be- 

 tween chert and shale. 



Occasionally one may find rather large bodies of well bedded 

 greenish or gray chert. These cherts show an occasional residual core 

 of red chert on the interior of the beds. They appear to have once 

 been ordinary red cherts, altered by leaching or reduction of the iron. 

 Often they contain considerable pyrite in specks, crystal grains, and 

 small masses and the decoloration may be due in part to the reduction 

 of iron oxide by the solutions which deposited the pyrite. Appar- 

 ently part of the iron has been removed — perhaps it has gone into the 



