A Text-Book of Geology for Use in Universities Volume 1. This item is unavailable.A Text-Book of Geology for Use in Universities Volume 1

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1920 Excerpt: ...observatories, clocks, ete. See Fig. 191. By other mathematical methods the distance below the epicenter of the focal point was calculated. These methods led to discordant results for a given earthquake, and eventually to the discovery that there might be several epicenters situated in a line, or that where earthquakes habitually occurred in a given region the epicenters were situated on this line. Further investigation showed that these were fault lines and this led to the present understanding of their cause, as previously stated. Thus the former ideas of a focal point, of its depth below the surface, etc., have in large measure lost their significance Recent Examples.--On August 31, 1886, the city Fig. 191.--Map of of Charleston in South Carolina was visited by a coseismic lines. severe earthquake which killed and wounded a number of people and did great damage to buildings and other structures. The shock was distinctly felt as far away as Chicago, a distance of 800 miles. It has been suggested that this was caused by the sudden slipping seaward of vast masses of sediment accumulated on a descending coast-line, but the attendant phenomena leave little doubt that like most other earthquakes it was due to the settling and adjustment of shell blocks. On May 3, 1887, a tremendous earthquake occurred in the province of Sonora in northern Mexico. It was felt over the greater part of Xew Mexico and Arizona, but as these were then very thinly settled regions little damage was done. The fault occurred at the base of a mountain range which was uplifted in places twenty feet. In 1899, a great earthquake took place in southern Alaska. As the region is mostly uninhabited it passed almost without notice at the time. Studies which have since been made show that conside...