REVIEWS 78l 



During the post-Miocene interval, it is probable that all the islands then 

 differentiated were mountainous masses belonging to the mainland. Judging 

 from their topography, and the apparent genetic relationships of those of the 

 northern group, the forms then existing probably included all the present 

 islands, except San Nicolas and San Clemente. The lafter appears not to 

 have been elevated till the close of the post-Miocene period, or early in the 

 Pliocene depression, and it is probable that the elevation of San Nicolas 

 occurred at about the same time. The disturbance at this time seems to 

 have been general for this whole region, including both faulting and folding, 

 and leading not only to the differentiation of these two islands, but also, 

 probably, to a greater elevation of all the other islands. Although the forces 

 operative in these movements are believed to have acted intermittently from 

 that time to the present, it is thought that they were mainly effective then ; 

 and that any later movements have been of minor importance in relation 

 to the general movements of the California coast, since the highest 

 elevated terraces of San Clemente and the leveled summits of Santa Cataline 

 and Santa Rosa still closely correspond in altitude with the highest terraces 

 on the mainland, and, going farther north, with the upper limit of the Pliocene 

 delta deposits along the Tres Pinos Creek. 



The post-Miocene elevation of the coast was followed by the Pliocene 

 depression, during which the sea stood for a long time some 1500 feet below 

 [above ?] its present level as shown by the highest terraces, the planation of 

 the island summits, and the delta deposits just referred to. Whether this 

 was the full extent of this depression for the southern coast cannot be stated 

 from the evidence at present available. During this depression, at first 

 Santa Cataline, San Clemente, San Pedro Hill, Santa Cruz, and Santa Rosa, 

 all probably existed as islands; or, in the case of Santa Cruz and Santa Cataline, 

 as two or more small islands. At this level the ocean remained, cutting 

 away the tops of these islands, till in the case of San Pedro Hill, and perhaps 

 of Santa Rosa also, they were probably wholly truncated, leaving submarine 

 banks like those of the region today. It is possible that San Nicolas was 

 also above sea level at that time, and has since been planed off to its present 

 lower level. Of San Clemente there remained a small nucleus, near the 

 center of the northern half of the island. Santa Cataline was reduced to a 

 small island lying to the north of the center of the present larger division of 

 the island, with probably one or more . distant rocks, or smaller islands, 

 toward the present extremities of the island. Santa Cruz, at that time pro- 

 bably existed as a single narrow island, or a line of islands, with a length of 

 at least seven miles, and formed from the northern ridge of the western or 

 main division of the present island. Then, as now, Santa Cruz was probably 

 the highest, if not the largest, of the existing islands. 



This depression was followed by a post-Pliocene elevation, as shown both 

 by the present elevation of the Pliocene deposits, and by the elevated coastal 



