[Sidenote: Fire kindled by natural causes was probably used by men long before they learned to make it for themselves.] Whether or not tribes ignorant of the means of making fire have survived to modern times, it seems likely that mankind possessed and used fire long before they learned how to kindle it. In the violent thunderstorms which accompany the end of the dry season in Central and Eastern Africa, it is not uncommon for the lightning to strike and ignite a tree, from which the fire soon spreads to the withered herbage, till a great conflagration is started. From a source of this sort a savage tribe may have first obtained fire, and the same thing may have happened independently in many parts of the world.[821] Other people, perhaps, procured fire from volcanoes, the lava of which will, under favourable circumstances, remain hot enough to kindle shavings of wood years after an eruption has taken place.[822] Others again may have lit their first fire at the jets of inflammable gas which spring from the ground in various parts of the world, notably at Baku on the Caspian, where the flames burn day and night, summer and winter, to a height of fifteen or twenty feet.[823] It is harder to conjecture how man first learned the great secret of making fire by friction. The discovery was perhaps made by jungle or forest races, who saw dry bamboos or branches thus ignited by rubbing against each other in a high wind. Fires are sometimes started in this way in the forests of New Zealand.[824] It has also been suggested that savages may have accidentally elicited a flame for the first time in the process of chipping flints over dry moss, or boring holes with hard sticks in soft wood.[825]