Throughout the disturbed district there were numerous depressions known as _sink-holes_, or irregularly shaped pits, varying from ten to thirty yards across, and having a depth of about twenty feet. These were formed by the forcible ejection of large quantities of water mixed with sand. New Zealand has been subject to earthquake shocks for a long time, the years 1826, 1841, 1843, 1848, and 1855 being especially marked by such visitations. It is a characteristic of the New Zealand earthquakes that they have produced a marked change in the coast line. This was particularly the case with those of 1848 and 1855. The 23d of January, 1855, an earthquake occurred that was most violent in the narrowest part of Cook's Strait, a body of water separating the two principal islands that constitute New Zealand; or, as they are called, the North Island and the South Island. These shocks were felt at sea by ships 150 miles from the coast. The entire area shaken, including the water, has been estimated at three times the area of the British Isles. In the vicinity of the southern shores of the North Island a tract of land having an area of 4,600 square miles is believed to have been permanently raised from one to nine feet. The earthquakes in New Zealand are evidently of the tectonic type. During that of 1848 a rent or fissure was formed, which, though but eighteen inches in average width, yet extended for a distance of sixty miles in a direction parallel to one of the mountain chains. On the 31st of August, 1886, an earthquake of considerable intensity occurred in the United States in the neighborhood of the city of Charleston, South Carolina. The details of this earthquake were carefully studied by Major Dutton of the U. S. A., and published in the Ninth Annual Report of the United States Geological Survey of 1888. Charleston is situated on a narrow tongue of land between the Ashley and the Cooper Rivers, about seven miles from the Atlantic Ocean. There are in this area numerous creeks connected with the drainage of these rivers. As the city limits extended, the creeks were filled in, forming "made land," all buildings or structures erected on this land being supported by pilings. It appears that the point at which the earthquakes started was situated sixteen or seventeen miles from Charleston. The earthquake shock affected a large area of the United States. Fig. 49 shows curved lines called isoseismal connecting places, having the same degree of seismic intensity. This map shows that these isoseimals are marked by figures or numbers from two to ten. These numbers are the numbers of the Rossi-Forel earthquake scale. They indicate varying degrees of intensity, beginning from the least intense shock which is marked as two and ending with the severest shock marked as ten. There is one degree not marked on this map, the least, called the micro-seismic shock.