There're two forms of geographic speciation. The classical one is where a continuous range of a species is being interrupted by a newly arising barrier, either a mountain range coming up or arm of the oceans going across or a desert or savanna developing in a forest area, and that is the one that is described in most of the books, at least in the early period from the 1930s on. But as I found in my work on the South Sea island birds, a far more frequent form of speciation is when a species develops a new colony, a founder colony beyond the species range, by some individual crossing over unsuitable terrain on… beyond the species range and establishing this new colony which eventually expands into a large population and, owing to this barrier between it and the mother country and the mother species, eventually develop into a new species, and I called this peripatetic speciation.