Page:Popular Science Monthly Volume 69.djvu/310

306 Bay opened for a short distance to the southward of Milpitas. But the soft soil in that region was filled with slumps and cracks due to the shaking down of loose deposits, and one could not be sure that the actual fault in the rocks was really disturbed. The same remark applies to the breaks at San Bruno about ten miles south of San Francisco in marsh deposits over the recognized San Bruno-Lake Merced fault. It is readily conceivable that a great disturbance like the one in the main fault might be accompanied by similar breaks in parallel or associated faults.

The chief center of disturbance in the earthquake of 1906 would seem to be in the sea. The evidence for this lies in the fact that at the point where the fault enters the land near Point Arena the displacement is greater than anywhere else. As the land fault is traceable for nearly two hundred miles to the southward, it is reasonable to suppose that the sea-bottom is broken for at least an equal distance to the northward. The point of earthquake disturbance oft Cape Mendocino has been frequently noticed in the past, and this is in a right line with the rest of the fault. It is possible that the center of trouble is located in the valley between Cape Mendocino and the off-lying submarine mountain.

There is also another possibility, very remote perhaps, but still worth considering, that is, the connection between this rift and the disturbances about the islands of St. John Bogoslof, in Bering Sea. In the year 1768, to the north of the island of Umnak and about :seventy miles northwest of Unalaska, a large island arose from the sea, In an earthquake disturbance. This island, Old Bogoslof, recorded by Captain Cook, was, as the present writer recalls it, about two miles long and fifteen hundred feet in height. In 1796, in another seismic disturbance, an addition was made to this island. In 1883 (October 28) a second island, of about the same size, arose, also from the sea, to the northward of the first. A photograph in my possession, taken in 1892 by Mr. N. B. Miller, of the steamer Albatross, shows this island, still hot and steaming. In 1896, when I visited it, it was apparently cold. These islands are supposably parts of the sea-bottom with a backing of melted rock, forced to the surface by pressure. On October 30, 1883, a severe earthquake was reported off Cape Mendocino. If on a globe one extends the axis of the Portolá-Tomales-San Andreas fault as far as Alaska, it would not fall far from these Bogoslof Islands. This fact suggested to the writer that possibly the earthquake of 1906 meant the birth of another Bogoslof. And it appears that this indeed was the case. The scanty reports which have reached us from the visit of the Albatross in May tell us that a third Bogoslof 'five times as large as either of the others' and between them, has arisen, and according to Captain Dirks, who