220 JAMES PERRIN SMITH 



important group consists of deep-seated granitic rocks, granites, 

 grano-diorites, diorites, and .gabbros, compounds of feldspars and 

 ferro-magnesian minerals, such as hornblendes, pyroxenes, and mica. 

 The greatest of these batholites is the great igneous mass of the Sierra 

 Nevada, making up the bulk of that mountain chain. Smaller 

 batholites of similar character are in the Sierra Madre Range, the 

 White Mountain Range, the Klamath Mountains, and in the Santa 

 Lucia Mountains. 



Associated with the deep-seated granitic rocks in nearly all these 

 regions there are numerous dyke-rocks, similar in chemical nature 

 to the parent masses, but showing only a small surface area. 



A second group is composed of basic intrusives, chiefly peridotites, 

 now largely changed to serpentine, rich in olivine and other ferro- 

 magnesian minerals. These cover great stretches in the Coast 

 Ranges, where they are largely of Franciscan age, older than the 

 Cretaceous; they also form less extensive masses in the Sierra Nevada. 



A third group is composed of lavas, mostly andesites and basalts, 

 surface flows from volcanoes. These are chiefly of Tertiary age, 

 Middle Miocene, and, together with the less important rhyolite flows, 

 they cover broad areas in northeastern California, and smaller patches 

 in all the other mountain regions of the state. The flows in north- 

 eastern California are a part of the Columbian field, and doubtless 

 came from fissure-eruptions. The others came from ordinary vol- 

 canoes, though in most cases the volcanic cones are long since 

 destroyed. Mt. Shasta and Lassen Peak are the two. grandest vol- 

 canoes of the state, the southern extension of the Cascade Range, 

 still preserving their ancient form and some feeble remnants of their 

 old-time activity. 



Inorganic sediments. — The greater part of the surface of California, 

 a little more than half, is made up of sediments. These are of two 

 groups, (i) inorganic, and (2) organic. 



The inorganic sediments are far greater in thickness and areal 

 extent, sandstones and shales, derived from the decay of crystalline 

 rocks. The quartz and undecomposed feldspars furnished the sand 

 grains, and the decomposed feldspars furnished the clay for the 

 shales. The sandstones of California are remarkable for the large 

 quantity they contain of undecomposed fragments of minerals derived 



