PETROGRAPHICAL NOTES. 17 



c, bluish -green), are partly chloritized, and, besides, fine 

 needles of actinolite are scattered throughout the rock. 



In a specimen from Gallo Canon, the uralitization is also 

 complete, and often the feldspar grains, irregular or lath- 

 like, are surrounded by uralite grains in a peculiar manner, 

 so as to give a somewhat clastic appearance to the rock. 



Using the term metamorphic in its wider sense, we may 

 refer to the rocks described under IV and V, as the meta- 

 morphic series. The general character of this series is not 

 unlike that of the Sierra Nevada, in which altered clastic 

 rocks, distinctly stratified, frequently alternate with massive 

 or imperfectly slaty diabases; it is also auriferous, contain- 

 ing, for instance, at Real del Castillo and other places, 

 numerous quartz veins with free gold. 



Gneisses and true mica schists are absent except, perhaps, 

 near the granite contacts, where the slates often become 

 strongly micaceous. 



The age of this auriferous slate series of Baja California 

 mQst, for the present, remain uncertain. From the occurrence 

 of unaltered, nearly horizontal cretaceous strata on the west 

 coast we may, however, conclude it to be pre-cretaceous. 

 On the other hand, there does not appear any reason why it 

 should be regarded as Archaean. There are in the Sierra 

 Nevada, at least, strata of carboniferous age or even possi- 

 bly younger, full}^ as highly altered as those here dis- 

 cussed. 



2d Skr., Vol. 11. Issued June 29, 1889. 



