ZS2 SOILS l.\ REFERENCE TO CLIMATE. 



of the Southern Ocean, a brilliant vegetation is seen along the course 

 of the few rivers which traverse them ; all beyond is dust and ster- 

 ility. I have seen rich crops of maize gathered upon the plateau of 

 the Andes of Quito in a sand that was nearly moving, but which 

 was abundantly and dexterously irrigated. 



A sandy and little coherent soil is by sc much the more favorably 

 situated as it lies in the least elevated parts of a district ; it is then 

 less exposed to the effects of drought ; any considerable degree of 

 inclination is unfavorable to such a soil, inasmuch as the rain drains 

 off too quickly, and because it is itself apt to be washed away. It 

 is to prevent this action of the rains, that the abrupt slopes of hills 

 are generally left covered with trees ; and the deplorable conse- 

 quences which have followed from cutting down the woods in moun- 

 tainous countries are familiarly known. 



Strong soils, on the contrary, are better placed in opposite cir- 

 cumstances. A certain inclination is peculiarly advantageous to 

 them ; and, indeed, in working clayey lands that stand upon a dead 

 level, we are careful to ridge them in such a way as to t'avor the 

 escape of water. 



In countries situated beyond the tropics, where consequently 

 shadows are cast in the same direction tliroughout the whole year, 

 the exposure of a piece of land is by no means matter of inditTor- 

 cnce. In our hemisphere, the lands which have a considerahle in- 

 clination and a northern exposure, receive less heat and light, and 

 remain longer wet than those that slope towards the south ; vegeta- 

 tion consequently is less forward upon the former than the latter 

 lands : but, on the contrary, the latter are less exposed to surfer 

 from want (jf rain ; and it is a fact, now well ascertained from data 

 collected in Switzerland and in Scotland, that the slopes which de- 

 scend towards the north, if they be only not loo abrupt, are actually 

 the most productive. This kind of anomaly is explained by the fre- 

 quence and rapidity of the thaws which lake place upon slopes that 

 lie to the south. Frost, when not too intense, is certainly less inju- 

 rious to vegetables than too rapid a thaw ; and it is easy to umler- 

 sland that in situations where, from the mere efiect of nocturnal 

 radiation, vegetables are covered almost every morning through the 

 spring with hoar frost, a rapid thaw must take place every day im- 

 mediately after the rise of the sun. With a northern exposure, the 

 frost occurs in the same measure ; but the cause (»f its cessalitm 

 does not operate so sutldenly, the fusion of the rime being eti'ectod 

 by the gradual rise in temperature of the surrounding air. In other 

 respects, it is obvious that the advantages and disadvantages of dif- 

 J'erent exposures are connected with the nature and the constitution 

 of soils. The same may be said with reference to means of shelter 

 from the action of j)revailing winds. Stiff wet lands are nuich bene- 

 fited by the action of free currents of air; our stilf soils at IJechel- 

 bronn remain impracticable for our ploughs during but too long a 

 period of the spring, when they have not been well dried in the 

 months of March and April by strong winds from the east. Light 

 and sandy soils, again, require to be well sheltered. The whole ob- 



