'Where there's muck, there's brass." In the north of England "brass" means "cash," but the old adage about dirt and money still rings true. And you don't get much muckier than an overcrowded seabird colony on a small Atlantic island.
By the time the first Western merchant-adventurers discovered the bleak, unlovely, offshore rocks of southwestern Africa, guano (originally a Peruvian word for bird excrement) had accumulated to depths of over 5 meters -- and rising.
This find caused great excitement. Not only can guano be used in the manufacture of explosives, it also makes superb fertilizer. In the 1800s, a ton of the stuff could fetch 10 British pounds or more in London -- a tremendous sum at that time.