INFLUENCE OF CLIMATE ON PLANTS AND ANIMALS. 225 



State the temperature is less than is clue to elevation and latitude. Now it might be inquired 

 whether the more uniform state of the atmosphere as to temperature is not due to geological 

 causes, or more specially to its geological formations 1 I think not : we are to leave out height 

 of course, which is due to a geological cause ; we know of no facts which go to prove that a 

 certain geological formation increases or diminishes the temperature of a region, aside from 

 height and the relations which they may bear to water ; that is, a slate or a shale produces the 

 same influence in temperature that granite, gneiss or mica slate would, under the same circum- 

 stances. Besides, we know that there is a sufficient cause in the direction of the wind, and in 

 the proximity to water, to produce the changes which have been noted. The rocks bear cer- 

 tain relations to water, which are always proper to notice ; it is, however, the condition of the 

 rocks, and not the mineral character, which is principally operative in producing a given result. 

 Thus slate rocks, which have been pressed together in the upheavals which have taken place, 

 become more impervious to water than if they had remained in a horizontal position. Lime- 

 stone is frequently traversed by natural joints or cracks, which, in the course of time, have 

 been widened, and hence water penetrates through the layers of limestone, and the soil resting 

 upon the rock becomes dry. It even becomes excessively dry under those circumstances ; or in 

 other words, the soil is too thoroughly underdrained^ and total barrenness is sometimes the 

 result. This is the case of a tract of country in Kentucky, called the barrens, and it is a case 

 which shows the possibility of lands being too much drained, and confirms the truth of the 

 doctrine which I have desired to inculcate in some of the foregoing remarks on draining. 



THE INFLUENCE OF CLIMATE ON PLANTS AND ANIMALS. 



It is difficult to determine the influence of climate on organized beings. The influence of 

 climate seems, however, to modify what exists ; it spends itself in those bounds ; it does not 

 form, but modifies varieties. Light, no doubt, should be regarded as an element of climate ; 

 its duration and intensity are indications of its force and measures its activity. We see the 

 foliage of a forest becoming more deeply green as we go towards a tropical region ; the herbage 

 of a species of forest tree becomes stiffer, rigid and less leafy as we go north, or ascend the 

 mountains, and we may trace the changes in our ascent, until we find it a dwarf, a diminutive 

 tree, a mere shrub upon the heights of a mountain, while in the plain at its base it is a lordly 

 tree. Those changes are unquestionably due to climate ; they are not those which characterize 

 varieties, much less species. Indeed it is important that we do not assign too much to climate. 

 Some naturalists have supposed that climate produces varieties ; it seems, however, more con- 

 sonant to facts to infer that varieties are independent of climate ; that the causes which have 

 been operating in the production of varieties have belonged to individuals. These forces or 

 influences are begotten in a civilized state, or where many individuals are congregated. 



It is not agreeable to the principles of natural history to maintain that the peculiar vegeta- 

 tion under a tropical sun is due to climate, or that it is an effect of climate. The species of 

 plants belonging to the tropics differ entirely from the temperate ; their characters are those 

 [Agricultural Report — Vol. hi.] 29 



