CHARACTER OF THE OLDER ROCKS. 385 



morphic rocks of the Coast ranges described as such by Mr. Becker in his 

 monograph on quicksilver deposits. Phthanite, mica schist, glaucophane 

 schist, diabase, amphibolite, with considerable metamorphic sandstone (in 

 which the sand grains are plainly discernible), together with some small 

 serpentine areas of uncertain origin on the southern slope of the mountain, 

 form the metamorphic area. The metamorphic sandstones are much frac- 

 tured, and are penetrated by numerous minute quartz veins. They contain 

 also a large amount of calcite, largely in little bunches. 



On the summit of the mountain there is a good deal of diabase, the origin 

 of which is uncertain. Under the microscope it is found to contain som • 

 serpentine in thin streaks and patches, but also much augite, the feldspar 

 being mostly decomposed. 



Most of the rock of North peak appears to be a greatly decomposed 

 diabase. It is, at all points examined, greatly crushed, and, like the meta 

 morphic sandstone, contains veins of quartz and veins and bunches of cal- 

 cite. This is true likewise of a good deal of the diabase found in patches, 

 intermingled with silicified shale and metamorphic sandstone, in other por- 

 tions of the metamorphic area. 



The silicified calcareous shale (phthanite) is especially abundant on the 

 southern and western slopes of the main peak. It occurs elsewhere, how- 

 ever, in patches at numerous points. Mica schist was found at one point 

 only, two miles southeast of the main peak. Glaucophane schist is rather 

 abundant, usually near serpentine. It occurs nowhere in any large body, 

 forming only isolated croppings or narrow streaks. It may be seen on the 

 ridge joining North peak and the main peak about one-half mile northeast- 

 ward from the main peak. 



About a mile and a half southwest of the main peak, near the edge of the 

 metamorphic area and not far west of the road from the Railroad ranch to 

 the Mountain house, there is some glaucophane schist so related (in part 

 interbedded) with the shale about it as to lead one to suppose it to have 

 been formed from the shale by the action of mineralizing solutions. 



The Pre-Tertiary Igneous Rocks. 



To the north of the metamorphic area there are two considerable areas of 

 crystalline rocks thought to be of igneous origin. One of these is a diabase, 

 and the other is a peridotite in some portions and pyroxeuite at the other 

 points, much of it having been altered to serpentine. 



Diabase. — The larger and probably the older of these two areas is, in its 

 most characteristic development, a typical diabase. 



It forms an area of about four square miles lying north of the serpentine 

 dike to be hereafter described, and embracing the points known on a map 



