THE HUMAN SPECIES. 177 



the well-known proceedings of subsequent ages, it is 

 clear, that outcasts and scouts, then hunter families, 

 would naturally be the first adventurers, and tribes 

 would follow onwards only as far as immediate neces- 

 sity or convenience might dictate ; pushing further 

 when more was known of the world before them, and 

 pressure from new colonists urged them from behind. 

 Starting through the gorges of the great river outlets 

 to the plains, and following their course, or ranging 

 along the flanks of mountain chains, to turn deserts, or 

 escape the necessity of attempting elevated ridges or 

 interminable swamps, which were or might be impas- 

 sable ; while, at the same time, water, game, and wild 

 fruits would be most abundant. 



Deserts and plains are never so absolutely impassable 

 as to prevent ulterior progress. Water is found in 

 some localities, and occasionally verdure ; and these 

 oases are soon marked by the wanderer, who then 

 guides his family or moving tribe along them, till 

 they reach a better region. Impediments of this kind 

 are therefore incentives to progress, and generally 

 much less obstacles than morasses and dense forests ; 

 for it is by the river courses alone that these last are 

 penetrated. 



In the progressive colonization, some leading tribe 

 would find a natural obstacle to retard or prevent its 

 further migration ; halting on the spot, other clans 

 would come up ; and where no forests near the sea, nor 

 a great stream, would favour the structure of rafts or 

 canoes, intercourse occurring, more or less knowledge 



M 



