Barbot, after mentioning a famine that happened in North Guinea in 1681, which destroyed many thousands of the inhabitants of the Continent, and forced many to sell themselves for slaves, to only get sustenance, says these fearful famines are also some years occasioned by the dreadful swarms of Locusts, which come from the eastward and spread over the whole country in such prodigious multitudes, that they darken the very air, passing over head like mighty clouds. They leave nothing that is green wheresoever they come, either on the ground or trees, and fly so swiftly from place to place, that whole provinces are devastated in a very short time. Barbot adds, terrific storms of hail, wind, and such like judgments from Heaven, are nothing to compare to this, which when it happens, there is no question to be made but that multitudes of the natives must starve, having no neighboring countries to supply them with corn, because those round about them are no better husbands than themselves, and are no less liable to the same calamities.[331] Of a swarm, which in the year 1693 covered four square miles of ground, a German author has made the following estimate. Observing that, when he trod on the ground, at least three were crushed, and that in a square German measure, less than an English foot, ten were destroyed; and after determining the number of these square measures in the four miles, he concluded that ninety-two billions, one hundred and sixty millions of Locusts were congregated on the surface. This is altogether a very moderate calculation, for not only is their number more compact in breadth, but they are often piled knee-high on the earth.[332]