Page:The origin of continents and oceans - Wegener, tr. Skerl - 1924.djvu/212

186 by the well-known fault connected with the earthquake of San Francisco on April 18th, 1906, shown in Fig. 41 (taken from Rudzki). The eastern portion was thrown southwards, the western northwards by it. The survey measurements, as was to be expected, showed that the amount of this sudden displacement gradually became less with increasing distance from the fracture, and at a great distance was no longer recognizable.

The crust of the earth had naturally been in slow continuous motion before the displacement at the fault. Andrew C. Lawson has compared this movement between the years 1891 and 1906, with the direction of the fault movement. He arrives at the conclusion based on the Point Arena group of observations, and shown in Fig. 42, that an object on the surface above the latter fracture has moved in the fifteen years about 0.7 m. from A towards B, then was divided by the formation of the fracture whereby the western half was thrown about 2.43 m. towards C and the eastern about 2.23 m. towards D. The continuous movement between A and B, which must be regarded as relative to the main mass of the North American continent, shows that the western margin of the continent is kept back continually to the north by attachment to the sima of the Pacific. The fracture only signifies a sudden adjustment of the stress, and does not move the continental block as a whole.