4 ON CHANGES IN THE DISPOSITION 



along the surface, must have been far greater than any 

 system of rivers now indicates. That question must be 

 reserved, though we must seek the explanation of many 

 appearances in this state of things ; not, as they have 

 been commonly sought, in those actions of rivers which 

 we now witness and to which I must at present limit 

 myself. The waters, thus draining along the declivities, 

 hastened to the lowest levels, by the channels which 

 the irregular elevations of the rocky surface must have 

 produced ; uniting into main trunks, and leaving lakes 

 in their courses, as they do at this day. It is true, that 

 the rivers of our own days are not those of antient 

 times ; yet whatever may be their actual direction, their 

 general course was determined by the positions, alti- 

 tudes and inclinations of the elevated strata. If the 

 present chains of mountains have been lowered, and 

 their forms rendered more'complicated by the enlarge- 

 ment and multiplication of their vallies, they still oc- 

 cupy the same places ; while, with the nature of the 

 rocks and the inclinations of the strata for our guides, 

 we can safely infer that the general division of the 

 waters over a given country is the same now as it was 

 from the beginning. Near their sources however, they 

 probably still correspond exactly ; the present ravine 

 being an enlargement of the original fissure, as the 

 mountain valley occupies the depression which first 

 tempted the waters to seek the present passage. If, 

 even in these higher elevations, the courses have some- 

 times been changed, in consequence of the waste of 

 the rocks, the general conclusion remains. It is in the 

 lower grounds that the great changes have occurred ; 

 since it is in these that they have either essentially mo- 

 dified, or even made their channels ; ever changing 

 them also, and unavoidably so, when they deposit the 

 very land through which they must construct a passage. 

 Thus, partly modified and partly made, the present 



