I 



On the Fall of Fivers. 309 



falls of rivers in general, as is shewn by the adduced in- 

 stances. 



Lieutenant Symond's measurements may therefore prove 

 perfectly correct ; and it is not at all necessary that any falls 

 should be discovered io account for the descent of the Jordan. 



But certainly there must be something to account for the 

 striking anomaly of Professor Robinson's results and my 

 own. The rivers which he draws up for comparison with 

 the Jordan exhibit more or less falls, and the two rivers 

 which I adduce here exhibit none. One might naturally sup- 

 pose that this was the consequence of incorrect data on either 

 side, upon which our results ai'e based ; but it is not so — it 

 is the anomaly which this feature of hydrographical develop- 

 ment exhibits ; and it is only from the deficiency of study in this 

 branch of physical geography, or rather the scarcity of data 

 for such a study, that this anomaly has not been fully explained. 



As the velocity of rivers does not altogether depend upon 

 the rate of their descent, in like manner the average fall does 

 not determine the formation of cataracts. It is much more 

 the geological character of the country through which the 

 river runs which causes those sudden descents ; and countries 

 where sudden declivities abound are chiefly of primary or 

 transition formation. We find striking examples in every 

 direction. 



The Severn and the Shannon, for example, are much alike 

 in magnitude. The latter descends, from Lough Allen to its 

 mouth, a distance of 213'8 English miles, 161 feet; the Se- 

 vern, from Newtown to its mouth, a distance of 210 miles, 

 descends 465 feet. This gives an average descent per mile 

 of 9 inches for the Shannon, and 26*6 inches for the Severn, 

 And yet the Severn pursues its course to the sea without any 

 rapids or falls ; whilst the Shannon, with its average fall of 

 one-third less than the Severn, forms those magnificent 

 Rapids of Doonas, which, for grandeur and effect, rank with 

 the most celebrated European waterfalls. 



The Tweed and the Clyde exhibit a still more remarkable 

 anomaly. Both are very much alike in point of magnitude : 

 the extent of their basins is 1870 English square miles for 

 the Tweed, and 1580 for the Clyde ; and they are still more 

 alike in point of their aggregate length and fall : the length 



