Page:The Journal of geology (IA journalofgeology21894univers).pdf/250
dation between the Miocene uplift and the depression which permitted the deposition on the lower flanks of the hill of the formations which paleontologists recognize as of Pliocene age. The recovery from this Pliocene depression is the uplift which is registered in the elevated strands of the hill." The uplift following the Pliocene depression is regarded as Pleistocene. This conclusion is of course warranted, if the Pliocene strata involved are known to belong to the closing stages of the Pliocene period. Otherwise it does not appear that the conclusion is a necessary one. Pleistocene strata are referred to as overlying the Pliocene, and as belonging to a recent stage of the uplift. Between the Pliocene and the Pleistocene no evidence of subaërial denudation exists.
On the west side of San Clemente Island seventeen well marked terraces occur, the highest at an elevation of 1320 feet. These terraces are from 200 to 1500 feet in width. There are less distinct terraces up to a height of 1500 feet. "The total amount of horizontal sawing which has been effected on the slopes of the island by wave action during its elevation through the last 1320 feet," is more than two miles.
Santa Catalina Island is of about the same size, trend, and height as San Clemente. It has a position midway between San Pedro Hill and San Clemente; but on Santa Catalina "there is no trace of an elevated wave-cut terrace, sea-cliff, or strand line of any kind observable." Furthermore, "The stream topography of the island is very much more advanced, i.e., much more ancient than that of either San Pedro Hill or San Clemente."
The absence of terraces and sea-cliffs cannot be attributed to the character of the rock, and their absence is in harmony with the condition of the stream valleys, which indicate that the island has not been below the sea in recent times; that is, "Santa Catalina has not been subjected to the uplift which has affected the two prominent insular masses, one twenty-five miles to the north of it, and the other twenty-five miles to the south of it." Not only has Santa Catalina not been elevated while San Pedro and San Clemente were undergoing the great uplifts which have been mentioned, but it is believed to have actually sunk while these other land masses were being lifted. The evidence of sinking is found in the drowned valleys of certain parts of the coast, and in the falls and rapids which mark the termini of the streams of other parts. Santa Catalina would appear to be situated in