Page:The Journal of geology (IA journalofgeology21894univers).pdf/251

the trough of a syncline which has been actually sinking while the lands on either side were rising.

The coast of the Bay of Monterey is also marked by a series of terraces. Four of them, the highest of which reaches an elevation of 712 feet, are very distinct, and abut against sea-cliffs. Higher terraces extend up to an elevation of 1201 feet. The river valleys also of the Santa Cruz region are found to afford evidence in harmony with that already cited from the regions further south. The general tenor of the evidence presented by this part of the coast is therefore in harmony with that presented by the more southerly region. Here also there has been a marked epeirogenic movement in recent times.

On the peninsula of San Francisco, marine Pliocene rocks, having a thickness of more than one mile, are said to exist. It is believed that subsidence accompanied the accumulation of this great series. These strata now occur at an elevation of over 700 feet. Not only this, but the strata have been so tilted, and subsequent erosion has been so great, that the base of the series, as well as the top, is exposed at this elevation. The elevation is said to have been post-Pliocene. Of course this is true, if the uppermost Pliocene strata involved represent the close of the Pliocene period.

According to the author, the relations of the Pliocene strata indicate great orogenic as well as epeirogenic movements in this region since their deposition. Montara Mountain is believed to have been produced during the orogenic event by which the Pliocene rocks (Merced series) were lifted into their present position. The granite axis of the mountain is regarded as the up-thrust base on which the Pliocene strata were laid down. All the adjacent younger strata dip away from this granite axis quaquaversally. While, therefore, the general structure of the mountain is comparable to that of a laccolite, it is, according to Professor Lawson, very different from it genetically.

On the basis of the facts given in the paper, there would appear to be no ground for doubt concerning the main conclusions at which Professor Lawson arrives concerning the movements of the coast in recent times. On the basis of evidence presented, there might be some question as to the post-Pliocene date of all these changes of level, did not Professor Lawson define the Pleistocene so as to include them. He says, (p. 159), "It is not an easy matter to delimit the Pliocene and Pleistocene epochs so that they shall correspond to the same divisions of the geological scale in the eastern part of the continent.....The rea-