REVIEWS 209 



Santa Catalina Island is one of the group known as the Channel 

 Islands, and lies about twenty miles off the coast of southern Califor- 

 nia. Its general trend is northwest by w^est, with a length of twenty- 

 one miles, and an average width of three miles. It is traversed from 

 end to end by a dominant ridge, culminating at 2100 feet. The gen- 

 eral character of the surface is bold and rugged, but it can be differ- 

 entiated into two topographic types, the one characterized as a young 

 topography, with steep sharp ridges and acute V-shaped canyons, and 

 the other as an older topography, composed of rounded forms, and 

 restricted to the higher portions of the island. In transverse section, 

 the island shows a general slope towards the mainland ; the valleys 

 on this side are broad and open, while on the ocean slope they are 

 "long and trough-like." The sea-cliffs, which make up the greater 

 part of the coast line, are in such rapid recession that the narrow 

 V-shaped canyons frequently merely gash their upper fronts, not having 

 been allowed time to cut down to sea level. 



A little more than half the island, including most of its western 

 half, is made up of a basement series consisting of quartzite, mica- 

 schists, talc and amphibolite-schists, and serpentine. The eastern 

 portion is mainly occupied by an intrusive mass of porphyrite (in 

 Iddings' sense) with accompanying dioritic dykes, and by andesitic 

 flows of later date. The various intrusive and effusive rocks are 

 described in detail, but present few features of general interest. The 

 occurrence of a small area of rhyolite is noteworthy on account of the 

 few cases in which rocks of this character have been described in the 

 Coast Range region of California. Its age relative to the andesite was 

 not determined. Some small areas of light-colored shale were found 

 on the northeast side of the island, associated with volcanic tuffs, and 

 w'ere correlated with the widespread Miocene shale of the Coast Ranges. 

 In this case the shale is shown to contain over 70 per cent, of opaline 

 silica, and to be made up largely of diatoms and forminifera, as identi- 

 fied by Dr. Hinde. 



The serpentines are derived from ultra basic eruptive rocks, and 

 are associated with small amounts of blue-amphibole-schist. the latter 

 probably the result of contact metamorphism. 



In a concluding chapter the writer ably sums up the geomorphog- 

 eny of the island. Submarine contours show that the Catalina land- 

 mass preserves its form down to a depth of 1800 feet. Near the shore 

 the water deepens rapidly down to 250 feet. At this depth a sub- 



