276 University of California Publications in Geology [Vol. 11 



of glaucophane running between angular masses of chert. Also occa- 

 sional veinlets of glaucophane are found in the red chert where no 

 other evidence of the change can be detected. Apparently the shale 

 partings were the most easily altered, since layers of soft glaucophane 

 schist occasionally appear between bands of little altered red chert. 

 The replacement of the chert by glaucophane schist and the preserva- 

 tion of the original bedded structure is so perfect that in a photograph 

 of this block the glaucophane schist cannot be distinguished from the 

 radiolarian chert. 



In the Santa Ynez Mountains a specimen of red chert was found 

 lying loose on the surface which showed a transition to glaucophane 

 schist. In its unaltered portion it is ordinary red chert which is cut 

 by several veinlets of a blue mineral. The unaltered red portion 

 passes imperceptibly into a very fine grained blue rock which is con- 

 siderably more porous in its texture than the red chert. 



Still other varieties of these metamorphosed rocks are to be found 

 in the form of large boulders of altered chert showing green, orange, 

 or vermilion colors. Running through these rocks in veins and form- 

 ing irregular masses within them there are considerable amounts of 

 blue amphibole. 



Cei-tain cherts with an indigo blue color owe this color to the 

 presence of a blue amphibole. These have been found in stream beds 

 as pebbles. In their physical appearance in hand specimens they are 

 like the ordinary cherts. They are very siliceous, show a conchoidal 

 fracture, and differ from other cherts only in color. They do not, 

 however, give evidence of radiolaria. In thin sections, they show a 

 siliceous matrix, through which runs a considerable number of minute 

 needles of blue amphibole. 



A specimen of indigo chert, in the collection of the University of 

 California, collected by Professor Lawson from North Berkeley, con- 

 sists of hard blue chert, in bands, separated by bands of soft bluish 

 material. The blue partings are found to consist of a mass of needles 

 of blue amphibole while the cherty layers consist of an aggregate of 

 quartz grains penetrated by numerous needles of blue amphibole. 



The origin of the glaucophane schists is of some interest in con- 

 nection with the present problem, as will appear later. The question 

 cannot be answered with absolute certainty at the present time in the 

 absence of numbers of careful analyses of altered and unaltered ma- 

 terial. A large part of the soda in the blue amphibole may have been 

 derived from the alkali in the shale partings in the original chert. 



