Earthquakes have a strongly marked geographical distribution. Most of them occur round the shores of the Pacific Ocean, though there are other regions where they are fairly common, notably parts of the Mediterranean basin, and the north Indian plain. In Ecuador, and in some other regions of folding, there are volcanoes. But it seems probable that the earthquakes cause the volcanoes, and not the other way round. Volcanoes also form at points where the earth's surface appears to be under tension, and tearing rather than folding. Volcanic regions of this sort are characterized by fissure eruptions when a relatively broad crack opens, and lava floods many square miles. Iceland is a region of this kind. The one efficient precaution against earthquakes is to make buildings as near as possible earthquake-proof, and to build cities in unstable regions so that fires will not spread; for water-mains are pretty sure to be broken by a severe quake.