The violent concussions often produce large fissures in the ground. Such were noticed in several places at San Francisco. One of the largest fissures known, that of Midori, in Japan, was caused by the earthquake of October 20, 1891. It left a displacement of the ground ranging up to 6 m. (20 ft.) in the vertical and 4 m. (13 ft.) in the horizontal direction. This crack had a length of not less than 65 km. (40 miles). Extensive fissures were also formed by the earthquakes of Calabria, in 1783, at Monte San Angelo, and in the sandstones of the Bálpakrám Plateau in India, in 1897. In mountainous districts falls of rock are a frequent consequence of the formation of fissures and earthquakes. A large number of rocks fell in the neighborhood of Delphi during the Phokian earthquake. On January 25, 1348, an earthquake sent down a large portion of Mount Dobratsch (in the Alps of Villach, in Carinthia, which is now much frequented by tourists) and buried two towns and seventeen villages. The earthquake of April 18, 1906, in California started from a crack which extends from the mouth of Alder Creek, near Point Arena, running parallel with the coast-line mostly inland, then entering the sea near San Francisco, and turning again inland between Santa Cruz and San José, finally proceeding _via_ Chittenden up to Mount Pinos, a distance of about 600 km. (400 miles), in the direction of N. 35° W. to S. 35° E. Along this crack the two masses of the earth have been displaced so that the ground situated to the southwest of the fissure has been moved by about 3 m. (10 ft.), and in some spots even by 6 m. (20 ft.) towards the northwest. In some localities in Sonoma and Mendocino counties the southwestern part has been raised, but nowhere by more than 1.2 m. (4 ft.). This is the longest crack which has ever been noticed in connection with an earthquake. [Illustration: Fig. 11.—Clefts in Valentia Street, San Francisco, after the earthquake of 1906] The earthquake over, the ground does not always return to its original position, but remains in a more or less wavy condition. This can most easily be observed in districts where streets or railways cross the ground. It is reported, for instance, that the track of the tramway-lines in Market Street, the chief thoroughfare of San Francisco, formed large wavelike curves after the earthquake.