3 o6 POPULAR SCIENCE MONTHLY 



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 ap- 

 plies to the breaks at San Bruno about ten miles south of San Fran- 

 cisco 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 dis- 

 placement is greater than anywhere else. As the land fault is 

 traceable for nearly two hundred miles to the southward, it is rea- 

 sonable 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 possibilit}', 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 pres- 

 sure. On October 30, 1883, a severe earthquake was reported off 

 Cape Mendocino. If on a globe one extends the axis of the Portola- 

 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 re- 



