I.] GENERAL CONSIDERATIONS. 15 



which lay the seats of the Peruvian, Chimu, Chibcha and Maya- 

 Quiche cultures ; the Aztec sphere alone ranged northwards a 

 little beyond the Tropic of Cancer. 



Thus in both hemispheres the iso-cultural bands follow the 

 isothermal lines in all their deflections, and the human varieties 

 everywhere faithfully reflect the conditions of their several en- 

 vironments. 



