1854J 



THE INFLUENCE OF AGRICULTURE ON CLIMATE. 



1*1 



it possessed characteristics which have not been alluded to by Mr. 

 Murray. 



In concluding these imperfect notes on the interesting pheno- 

 mena of the lakes, we have merely to express our entire concur- 

 rence in the views which are entertained by man} 7 , that the annu- 

 al variations are the result of climatic irregularities, and conse- 

 quently, entirely dependant upon waste and supply. The local 

 variations are unquestionably due chiefly to the influence of 

 winds, and in a far less degree to sudden variations in atmospheric 

 pressure, which produce the phenomena of seiches, as described 

 by Col. Jackson, on page 27 of this Journal. The violent and 

 local convulsions w : hich have been witnessed near Cobourg, and 

 elsewhere, appear to result from causes far more obscure, but ) r et 

 not altogether inexplicable. We shall return to the consideration 

 of these remarkable phenomena at some future period. The very 

 great difficulty of obtaining authentic information respecting 

 " lake convulsions," or any phenomena of a local character which 

 may have been observed and recorded, induces us warmly to 

 solicit from the members of the Institute, or the readers of this 

 journal, the communication of any facts or information which they 

 may think worthy of transmission. 



The following paper, from the rural economy of J. B. Bous- 

 singault, on 'the Influence of Agriculture on Climate in lessening 

 Streams,' contains matter of much interest, which can already be 

 appreciated in many ways by the people of Canada, and of the 

 shores of the great lakes. 



The Influence of Agriculture on Climate in Lessening 

 Streams, etc. 



(FROM THE " RURAL ECONOMY" OF J. B. BOCSS1NGAULT.) 



A question of great importance, and that is frequently agitated 

 at this time, is, as to whether the agricultural labors of man are 

 influential in modifying the climate of a country or not? Do 

 extensive clearings of woods, the draining and drying up of great 

 swamps, which certainly influence the distribution of heat during 

 the different seasons of the year, also exert an influence on the 

 quantity of running water of a country, whether by lessening the 

 quantity of rain which falls, or by promoting the more speedy 

 evaporation of that which has fallen ? 



In some districts it has been held, that the streams which had 

 been used as moving powers, have very sensibly diminished. In 

 other places, the rivers are said to have shrunk visibly ; and in 

 others, springs that were formerly abundant, have almost dried 

 up. Observations to this effect appear to have been principally 

 made in valleys, surmounted by mountains ; and it is generally 

 asserted, that the falling off in the springs and streams had fol- 

 lowed close upon the period at which the woods, scattered over 

 the surface of the country, were cleared away without any kind 

 of reserve. 



The lakes which are met with in plains, and at different levels 

 in mountain ranges, seem to me peculiarly calculated to throw 

 light on this subject. Lakes may, in fact, be received as natural 

 gauges of the running waters of a country. If the mass of the 

 water contained in the lakes undergo change in one direction or 

 another, it is obvious that this change, and the direction in which 

 it has occurred, will be proclaimed by the state or mean level of 

 the lake or lakes, which, will differ for the same reasou that it 

 does at different seasons of the year, viz. as drought or rain pre- 

 vails. The mean level of the lake or lakes of a district will, 

 therefore, fall, if the quantity of water which flows through that 

 •district diminishes; the level, on the contrary, will rise, if its 

 streams increase; and it will remain stationary if the afflux and 

 effliii of the Take continue unchanged. ' In'the folIowin« remarks 



I shall attach myself particularly to observations upon lakes 

 which have no outlet, by reason of the facility with which any, 

 even slight, change in the level of these must be discovered. I 

 shall not, however, neglect those lakes which have an exit by a 

 stream or canal, because I believe that the study of these may 

 also lead to accurate enough results ; the only point requiring 

 preliminary remark is the sense in which the words, change of 

 level, are to be taken. 



One of the most interesting portions of Venezuela is, undoubt- 

 edly, the valley d'Aragua. Situated at a short distance from the 

 seaboard, possessed of a warm climate, and of a soil fertile beyond 

 example, it combines within itself all the varieties of agriculture 

 that belong in peculiar to tropical regions ; on the hillocks, which 

 rise in the bottom of the valley, are seen fields which bring to 

 mind the agriculture of Europe. Wheat succeeds pretty well 

 upon the heights which surround La Vittoria. Bounded on the 

 north by a chain of hills, which run parallel with the sea-board, 

 and to the south by the range which separates it from Llanos, 

 the Aragua Vallej 7 is limited on the east and west by a series of 

 lesser elevations, which shut it in completely. In consequence of 

 this peculiar configuration of country, the rivers which lise in its 

 interior have no outlet to the ocean; their waters accumulate in 

 the lowest part of the valley, and form the beautiful lake Valentia. 

 This lake, which M. de Humboldt says exceeds the lake Neuf- 

 chatel in size, is raised about 1300 feet above the level of the sea ; 

 it is about ten leagues in length, and about two leagues and a 

 half where it is widest. 



At the time when M. de Humboldt visited the Aragua Valley, 

 the inhabitants were struck with the gradual diminution which 

 had been going on in the waters of the lake during the last thirty 

 years. It was enough to compare the statements of older writers 

 with its condition at this time, to obtain conviction that the 

 waters had, in fact, very much diminished. Oviedo, for instance, 

 who visited the valley frequently towards the end of the sixteenth 

 century, says, that the town of New Valencia was founded in 

 1555, at a distance of half a league from the lake; in 1S00, M. 

 de Humboldt ascertained that the lake was upwards of 4549 

 yards, or upwards of 3|- miles, instead of about 1^ mile from its 

 banks. 



The appearance of the surface also gives new r roof of the fact 

 of the recession of the water; certain hillocks which rise in tha 

 plain still preserve the title of islands, wdiich, undoubtedly, they 

 formerly received with propriety, when they were surrounded 

 by water. The land which had been left by the retreat of the 

 lake, soon became transformed into ber.utiful plantations of cot- 

 ton-trees, bananas, and sugar-canes. Buildings, which had been 

 erected on the banks, were left, year after year, further and further 

 from them. In 1796, new islets made their appearance. An 

 important military position, a fortress built in> 1740, in the Isle 

 de la Cabrera, was then upon a peninsula. Finally, in two islets 

 of granite, M. de Humboldt discovered, several yards above tha 

 level of the lake, a bed of fine sand mixed with fresh water shells. 

 These facts, so certain, so unquestionable, did not pass without 

 numerous explanations from the wise men of the country, who, 

 as if by common consent, fixed upon a subterranean exit for the 

 waters of the lake. M. de Humboldt, after the most careful 

 examination of all the circumstances, did not hesitate to ascribe 

 the diminution of the waters of the lake Valencia, to the exten- 

 sive clearings which had been effected in the course of half a 

 century in the Aragua Valley. "In felling the trees which 

 covered the crowns and slopes of the mountains" says this 

 celebrated traveller, " men in all climates seem to be bringing 

 upon future generations two calamities at once — a want of fuel 

 and a scarcity of water."* 



* Humboldt, vol. v. p. 173. 



