742 EDWARD H. NUTTER, WILLIAM B. BARBER 



Calaveras Valley. — In the northern end of Calaveras Valley, 

 northwest of Mount Hamilton, in Alameda county, there is an 

 area of glaucophane and related schists, which can best be studied 

 in the canyon of the Arroyo Hondo. There are two series of 

 glaucophane-bearing rocks in this locality; one a massive crys- 

 talline rock, one facies of which is an eclogite containing, princi- 

 pally, garnet, omphacite, glaucophane and actinolite. The other 

 facies is a medium grained, light colored, banded rock composed 

 principally of quartz, glaucophane, garnet, and white mica. The 

 garnets are in the form of very small crystals which are included 

 in the quartz and glaucophane. 



The other series of glaucophane-bearing rocks overlies this 

 massive one unconformably, and consists of thin bedded sandy 

 shales having a vertical dip and a northwesterly strike. They 

 are much contorted, however, and are hard and schistose in places. 

 These beds are unfossiliferous, but are overlain unconformably by 

 Lower Miocene sediments. They resemble to a large extent the 

 sandy shales of the Golden Gate or Franciscan series, and it seems 

 probable that they belong with those rocks. Glaucophane is 

 developed in them irregularly, one bed being blue with it, while 

 the adjoining one on either side may contain but little glaucophane. 

 White mica is developed in these beds in many places, and narrow 

 quartz veins are common. 



In the southern end of the canyon are masses of serpentine, 

 but the contacts between them and the adjoining rocks are not 

 exposed. 



In contact with the massive banded rocks is a hard, heavy, 

 compact, greenish rock, with bands and stripes of glaucophane 

 plentifully distributed through it. It may be an altered serpen- 

 tine, but thin sections of it show no definite minerals. It is 

 apparently a dike intrusive in the banded rock, but it has probably 

 been altered since, and may have been subjected to the same 

 agencies that produced the banded rock. 



Conclusions. — No one explanation seems to satisfactorily ac- 

 count for the many different aspects and occurrences of the 

 glaucophane and related schists. That there has been some 

 development of glaucophane at the contact of basic igneous 



