598 PHYSICAL GEOGRAPHY. 



clay for the purpose of allaying hunger. Humboldt found in their huts heaps of it in the 

 form of balls, piled up in pyramids three or four feet high. The substance is fine and 

 unctuous, of a yellowish-grey colour, containing silica and alumina, with three or four 

 per cent, of linie. 



In considering the distribution of mankind, it is an obvious reflection that, to secure 

 the general diffusion of human life, the same necessity did not exist, as in the case of 

 plants and animals, for parent stocks to be originally planted in different regions of the 

 globe. It has been correctly remarked, that had an individual of each tribe of plants, and 

 a pair of each tribe of animals, been called into being in one and the same spot, the 

 Linnsean hypothesis, large regions, separated by wide seas and lofty chains of mountains 

 from the country containing that single spot, would for ever have remained almost, if not 

 entirely, destitute of plants and animals, unless at the same time means had been provided 

 for their dispersion far more effectual than any which we behold in operation, and a 

 constitution more accommodated to diverse climates had been given to them. To accomplish 

 the dissemination of animal and vegetable life, to an extent commensurate with the 

 capacity of the globe, separate regions were supplied with distinct stocks of plants and 

 animals. But the case of man required no such arrangement to secure a large occupancy 

 of the earth with his species. Endued with a constitution capable of accommodating itself 

 to extreme diversities of climate, and with intelligence to invent methods of protection 

 against atmospheric influences ; enabled also by the same intelligence to devise means of 

 transport over the most extensive seas, and across the most formidable ranges of mountains, 

 it is clear, that, possessed of these capabilities, the whole habitable earth might be reple 

 nished with his race from the location of a single pair. This is the doctrine of the Mosaic 

 history, and also of another part of the sacred record, which declares that God " hath 

 made of one blood all nations of men for to dwell on all the face of the earth ;" and 

 notwithstanding numerous and important diversities, the conclusions of philosophical 

 inquiry are clearly in harmony with it, establishing the unity of mankind. 



Before touching upon the question of the common nature and origin of the human race, 

 a necessary preliminary to the question of their diffusion, it may be requisite to state the 

 sense of certain terms of common occurrence in natural history, as species, genus, and 

 varieties. A race of animals, or plants, which constantly transmit from one generation to 

 another the same peculiar organisation, constitute what is technically called a species; and 

 two races are held to be specifically distinct, where a marked difference of organisation 

 exists, which is unvaryingly transmitted. A species therefore includes those animals and 

 plants which may be presumed to have sprung from the same parent stock. " We unite," 

 says De Candolle, " under the designation of a species, all those individuals who mutually 

 bear to each other so close a resemblance as to allow of our supposing that they may 

 have proceeded originally from a single being, or a single pair." The term genus has a 

 more comprehensive signification. It is applied to a group of animals or plants, the 

 several tribes of which seem constructed after a common general model, each being 

 distinguished from the rest by a peculiarity of organisation, for which we cannot account 

 but by supposing them to have proceeded from originally different individuals. Animals 

 of the horse kind, which includes the ass and the zebra, furnish an example of genus. 

 They display the phenomena of general resemblance, but with such marked differences, 

 which are regularly transmitted, that we cannot suppose them the common offspring of 

 the same individuals, but to have descended from originally different pairs. Animals of 

 the feline race, as the cat and the tiger, and of the bovine kind, as the ox, buffalo, and 

 bison, are similar instances of genera. A genus therefore embraces several species. But 

 within the limits of a species varieties occur, or deviations from the type exhibited by the 

 parent stock, which are due to external causes, climate, soil, food, and other agencies, 



