ECLOGITES IN CALIFORNIA 355 



glaucophane schist. While the akeration is generally complete, he 

 found a volcanic neck where on one side the change is not entire, and 

 under the microscope augite is seen changing into glaucophane. The 

 feldspar has changed chiefly to epidote. Some green hornblende and 

 chlorite are present. An examination of several slides — kindly 

 loaned by Mr. Diller to Dr. J. P. Smith — shows that part of them 

 may be classed as glaucophane eclogites. One specimen from 

 Winston's Bridge is essentially glaucophane and garnets — the latter 

 2-3™""- in diameter. Mica, chlorite, sphene, and epidote are also 

 present. An analysis of this rock without the garnets, as given by 

 Washington,' is included in the table herewith. 



CONCLUSION. 



The question of the derivation of eclogites and of their place in the 

 series of metamorphic rocks is both interesting and difficult. In the 

 absence of direct proof for any special instance at hand opinions as to 

 the igneous origin of a metamorphic rock should be given with due 

 reservation. It seems to be well established that both igneous and 

 sedimentary rocks sometimes grade into schistose forms that appear 

 to be indistinguishable on first examination. From the evidence now 

 at hand the writer would conclude that the San Martin and the Cala- 

 veras eclogites are derived from basic eruptives of the gabbro type. 

 This derivation is indicated by their massive and irregular appear- 

 ance in the field as well as by the general field relations. 



The occurrence of the San Jose eclogite in the Oak Hill area of 

 igneous rocks indicates that we have there merely the modification of 

 a rock derived from the same magma as the basic eruptives that form 

 the hills. The igneous origin of the San Martin eclogite is also indi- 

 cated by the chemical analysis. As may be seen in the accompan3dng 

 table, the sihca is only slightly over 44 per cent. — which indicates 

 derivation from some very basic eruptive. The percentage of sihca 

 is very close to that given by Hezner in the two analyses which he has 

 made. Hezner thinks that his analyses show well the normal chemical 

 composition of eclogites. The table of analyses here given should be 

 supplemented by additional work on the California eclogites, but it 

 is at least suggestive in the comparisons which it aft'ords. 



I" Study of the Glaucophane Schists," American Journal of Science, Vol. CLXI. 



