12 ON CHANGES IN THE DISPOSITION 



the Mosaic deluge. The other case is more abstruse, 

 and of peculiarly difficult investigation. In either, the 

 source of the alluvia cannot be mistaken ; from that 

 regularity of stratification which can only occur in the 

 case of a river deposit, the facts being such as not to 

 admit of a former lake ; and if the original stream 

 cannot be found in the neighbourhood, the only re- 

 maining solution is, that of the lowering of the moun- 

 tains, through the usual waste ; thus cutting off that 

 supply of water which originally produced a large 

 river where there is now but a rill, or perhaps nothing. 

 Of such extensive losses of land there can be no doubt, 

 as I shall show hereafter; while it is obvious that 

 higher lands must have produced larger rivers. And 

 when I find that the most striking cases of this nature 

 occur at the foot of trap ridges, so especially bearing 

 marks of great waste, this solution becomes even more 

 satisfactory. 



In concluding this branch of the action of rivers, it 

 is now evident that I but partially agree with those 

 who, in their eagerness after a system, have asserted 

 that all valleys have been excavated by their rivers: 

 while it must be plain that the long-continued dispute 

 among geologists, whether the beds of rivers had been 

 prepared, or were made by themselves, is but the dis- 

 pute of children in this science. It is evident that the 

 original drainage consisted in the irregularities of the 

 elevated rocky surface; nor can I understand how this 

 necessity should have been overlooked by those with 

 whom this forms an essential part of the whole system. 

 Were the rivers the causes of the valleys, every land 

 should have been a table of mountain, without other 

 discontinuity than a fissure. Were this theory true, 

 how is there any lake at all ; above all, how are there 

 such lakes as Loch Ness, many hundred feet deeper 

 than the surrounding seas ? No river could have ex- 



