Lawson.] 



Geology of Car inch Day. 



43 



iron oxide, while the brownish laminae owe their color to the pre- 

 ponderance of brown iron oxide. In both areas the iron oxide, 

 whether black or brown, appears to be associated with the iddingsite 

 of the ground-mass; and in a series of slides all gradations may be 

 traced from crystals which are nearly or quite opaque, from dense 

 pigment, to those which are transparent, with only a little yellow 

 oxide associated with them peripherally. Throughout the ground- 

 mass, also, there may be seen in some of the slides, small, hazy, 

 greenish areas, which appear to be chlorite or serpentine. 



Imbedded in the ground-mass are large, well-formed crystals of 

 iddingsite, which are usually sufficiently free of pigment to allow of 

 satisfactory study of their optical character. 



The San Jose Area. — A crescent shaped area of carmeloi'te 

 encircles the head of the sharp, short canon which gashes the hill 

 immediately to the north of San Jose Creek near its mouth. The 

 rock here is usually of a greenish gray or purplish gray color, mot- 

 tled with white spots representing phenocrysts of plagioclase, and 

 also in some cases with larger irregular blotches of yellow limonite. 

 Phenocrysts of iddingsite may also be detected, but they are not 

 abundant. 



Under the microscope it is found to consist of the usual ground- 

 mass of lath-shaped plagioclase and iddingsite, with interstitial 

 glass and scattered granules of magnetite. In addition to the latter 

 ore, however, there is an abundance of limonite, both in small gran- 

 ules and in large, irregular patches. The iddingsite in this ground- 

 mass shows, perhaps, more definitely than in other cases an ophitic 

 relation to the lath-shaped plagioclase. Imbedded in the ground- 

 mass appear phenocrysts of fresh plagioclase and of iddingsite. 

 The presence of the phenocrysts of plagioclase allies the facies 

 rather with the occurrences at Sunium Point or the ravine area than 

 with those at Abalone Point, the lagoon, and the mission. 



Relation of the Carmeloite to Other Formations. — Having de- 

 scribed the petrographical character of the carmeloi'te, a word 

 remains to be said as to its structural and time relations to the other 

 formations of the vicinity. The petrographical description estab- 

 lishes its igneous character. The flow structure, the occasional 

 bedding, the presence of agglomerates and breccias, the vesicular 



