360 SYL.VA AMERICANA. 



embellishing to the landscape, yet there are certain circumstances 



connected with the growth of the various species of forest trees, 



which, when they occur, effectually control the choice of the 



planter in his modes of arrangement : these are, first, the peculiar 



nature of the soil to be planted; secondly, the climate, or the 



exposure and elevation of the site of the plantation. In planting, 



soils may be divided into simple and mixed. The latter allows 



of the fullest scope to mixed planting. Simple soils are those 



which contain the smallest number of ingredients in their 



composition, or which consist chiefly of one substance ; as sandy 



soils, containing from nine-tenths of sand to one twentieth, the 



supposed point of absolute sterility for even common herbage, 



are properly termed simple sandy soils, and on which the pine, 



fir, larch, and perhaps the birch, can only be planted. Soils 



consisting of from seven-eighths to a larger proportion of chalk 



will rear the beech chiefly ; and when the proportion of one half 



of vegetable matter to one half of sand and loam meet in a soil, 



it is properly simple vegetable earth, and comes under the 



denomination of peat, of which there are several kinds, but which 



will be more particularly mentioned under the head of soils. On 



this last-mentioned soil the planter is chiefly confined to the 



poplar and alder : the willow and birch only partially succeed, 



or when the vegetable matter is in a less proportion to the other 



ingredients above stated. 



The elevation of the sight of the intended plantation above the 

 level of the sea, where that is considerable, influences the local 

 climate so much as often to confine the choice of the planter to 

 one or two species of trees only, even though the soil should be 

 otherwise favorable for mixed planting. 



It is calculated that an elevation of six hundred feet diminishes 

 the temperature of a site equal to that of one degree of north 

 latitude ; the degree of dryness or humidity of the atmosphere, 

 and the force of the winds seem also to increase in proportion to 

 the elevation of the land. Accordingly we find that different 

 species of trees occupy different regions and degrees of elevation 

 on the mountains of the torrid, temperate and frigid zones. 



According to Humboldt, the trees which grow in the highest 



