VALLEY. 



aferibed almoft exclufively to the aftion of running water. 

 That many of the prefent valleys have been fo formed, is 

 I rendered probable by various exifting phenomena, but other 

 caufes mufl: alfo have operated. Among thefe we may 

 enumerate the original inequalities of the furfacc ; thefe 

 were indeed neceltary to make the waters flow in a par- 

 ticular courfe. The fudden elevation of parts of the earth's 

 furface, and the fubfidence of other parts, are alfo proved 

 by the fraftures and diflocations of the ftrata which moun- 

 tainous diilridls almoft every where prefent. There are 

 likewife evident marks that the ocean has been thrown fud- 

 denly, and with great violence, over our prefent continents, 

 tearing away and tranfporting to diftant countries various 

 parts of the furface, fcooping out hollows in the fofter 

 ftrata, breaking down the boundaries of immenfe lakes, and 

 thus changing the courfe of rivers, and opening new valleys 

 where none before exilled. Great and fudden rifings of the 

 fea have been known to take place in our times, by the 

 agency of fubterranean fire operating on a fmall extent of 

 the globe ; and we have only to conceive the fame agent 

 operating more powerfully, to explain the changes which 

 may have taken place from the ocean fuddenly riilng and 

 fweeping over a large portion of the globe. See System 

 of Geology. 



The theory of the formation of valleys by the aftion of 

 rivers has been fupported by Dr. Hutton and profeffor 

 Playfair. " Every river (fays the latter) appears to con- 

 fift of a main trunk, fed by a variety of branches, each run- 

 ning in a valley proportioned to its fize, and all of them 

 together fontiing a fyftem of valleys communicating with 

 one another, and having fuch a nice adjuftment ot the de- 

 clivities, that none of them join the principal valley either 

 in too high or too low a level, a circumftance which would 

 be infinitely improbable, if eaoh of thefe valleys was not the 

 work of the ilream that flows through it. When the ufual 

 form of a river is confidered, the trunk divided into many 

 branches, and thefe again fubdivided into an infinity of 

 fmaller ramifications, it becomes ttrongly impreffed upon the 

 mind, that all thefe channels have been cut by the waters 

 themfelves, and that they have been flov/ly dug out by the 

 wafhing and erofion of the land." This is an accurate 

 dcfcription of the ftrufture of many valleys, but there are 

 others in which the fmaller valleys do not join the larger at 

 the fame level, but terminate abruptly, and the rivers which 

 flow through them fall in cafcades to the lower valleys. The 

 valley of Wattenlagh, in Cumberland, is a ftriking inftance 

 of this kind. The lower extremity joins the vale of Kef- 

 wick, in which the lake of that name is fituated, but it does 

 not enter it at the fame level, but terminates in a precipice 

 between two cliffs, down which the water is thrown, form- 

 ing the cataraft of Lowdere, which empties itfelf into the 

 lake. 



Where the correfponding ftrata on each fide of a valley 

 have nearly the fame elevation as is reprefented in Plate III. 

 Geology, Jig. 4, it is obvious that the excavation between 

 the oppofite hills has been formed by water which has 

 once flowed at a much higher level than at prefent. Alfo, 

 where the ftrata on the oppofite fides of a valley have the 

 fame angle of inclination with the horizon, (fee Plate II. 

 Geology, fg. 5.) we may infer that it has been ex- 

 cavated by water : but where the ftrata on the fides of a 

 valley dip in an oppofite direftion, or have a much greater 

 dip on one fide than on the other, the original formation 

 of the valley may be attributed to the elevation or fub- 

 fidence of the ftrata, forming a fiffure through which the 

 water has run, and in the courfe of ages has worn down 

 and enlarged the paflage. Some circular valleys and lakes 



may have originated in the fubfidence of the furface, form- 

 mg a large cavity, the fides of which are gradually worn 

 down in many parts into gentle Hopes. An accurate exa- 

 mination of the true line of dip of the beds, can alone dif- 

 cover to which of thefe caufes the formation of any par- 

 ticular valley can be afcribed; and it is frequently more 

 difficult to afcertain the true angle of inclination than is 

 generally fnppofed, and ftill more difficult to determine 

 whether a flight variation in the angle is occafioned by a 

 frafture, or by an original inequality or waving of a 

 ftratum. 



That lakes are paffing to the ftate of valleys, and that 

 many of the prefent valleys have been lakes, is obvious to 

 the moft common obferver who will attend to the appear- 

 ances which they prefent. A lake, fays profeflbr Playfair, 

 is but a' temporary and accidental condition of a river, 

 which is every day approaching its termination ; and the 

 truth of this is attefted not only by the lakes that have 

 exifted, but by thofe which continue to exift. Where any 

 confiderable ftream enters a lake, a flat meadow is ufually 

 obierved incrcafing from year to year : the foil of this 

 meadow is difpofed in horizontal ftrata ; the meadow is 

 terminated by a marfli, which marfti is acquiring folidity, 

 and is foon to be converted into a meadow, as the meadow 

 will be into an arable field. All this while the fediment 

 of the river makes its wav flowly into the lake, forming a 

 mound or bank under the furfacc of the water, with a 

 pretty rapid flope towards the lake. This mound in- 

 creafes by the addition of new earth, mud, and gravel, 

 poured in over the flope, and thus the progrefs of filling 

 up gradually advances. By an accumulation of vegetable 

 matter in fliallow lakes, marffies and peat bogs have 

 been formed at the bottom of valleys where the waters 

 have not flowed with fufficient rapidity to drain away the 

 moifture. Thefe are common in various parts of the High- 

 lands, and in Ireland. The filling up of lakes, and the en- 

 largement of valleys, by the procefs above defcvibed, may 

 be diftinftly feen in the vicinity of the lakes of Cumberland 

 and Weftmoreland. Larger lakes exemphfy the fame pro- 

 cefs. Where the Rhone enters the lake of Geneva, the 

 beach has been obferved to receive an annual increafe ; and 

 the Portus Valefix, now Prevallais, which is at prefent half a 

 league from the lake, was formerly clofe upon its bank. 

 Indeed the fediments of the Rhone appear clearly to have 

 formed the valley through which it runs, to the diftance of 

 about three leagues from the place where the river now dif- 

 charges itfelf into the lake. The ground there is perfeftly 

 horizontal, compofcd of fand and mud, little railed above 

 the level of the river, and full of marffies. The depofiticn 

 made by the Rhone, after it enters the lake, is vifible to 

 the eye, and may be feen falling down in clouds to the 

 bottom. 



Wliere lakes are fituated at a confiderable elevation above 

 the fea, or the adjacent country, they may be emptied by 

 the wearing down of the ftrait which forms the outlet. 

 Many of the North American lakes are connefted by imall 

 ftraita or rivers, which have a rapid dcfcent. On fome ot 

 them are prodigious water-falls, which are conftantly en- 

 larging the pafi'age from one to the other, and will ulti- 

 mately drain the upper lakes. The falls of Niagara are 

 obferved to be progreffiveiy fliortening their diftance from 

 the upper lake, fince the banks have been inhabited by 

 Europeans ; and when it iias completed its progrefs, the 

 upper lake will become an extenfive valley, furronnded by 

 rifing grounds, and watered by a river or fmnller lake, 

 which will occupy the loweft fituation. 



Valleys conftitute the raoft fertile and habitable parts of 



alraolt 



