Force of Running Water increases xcith its Depth. 21 



low the level of the plain, the declivity between the plain and 

 the river forming an angle with the horizon of nearly 45°. Be- 

 sides the marks of ancient channels formed by the river, the 

 plain has been more recently intersected by ravines formed by 

 lateral torrents and by the draining of rain-water from its sur- 

 face. The subdivisions of these ravines, with the swelling pro- 

 minences between them, now covered with grass, exhibit in mi- 

 niature an exact copy of the forms of our chalk-hills. The 

 steep declivity of naked gravel, with disseminated boulder-stones, 

 is worn at some places by the rain into the sharp spires known 

 under the names of Erde-pyramiden and Chcmijiees des Fees, 

 which are seen developed in the greatest abundance and magni- 

 tude in the valleys above Botzen, and in other parts of the 

 southern flank of the Alps. 



An instance of the same mode of action, though with some 

 remarkable modifications, is exhibited nearer home in the bed 

 of the Mersey above Liverpool. Opposite to that port the river 

 is so narrow, that the stream, mainly produced by the rising 

 and falling of the tide, flows with great rapidity. Higher up the 

 Mersey opens, as Camden expressively states, " patenti gremio," 

 and assumes something of the aspect and nature of a wide lake. 

 The stream being here less active, in proportion to the expan- 

 sion of the channel, an abundant deposition takes place, and, at 

 low water, a very large portion of the bed is seen to consist of 

 banks of sand, which terminate before the narrowing of the 

 channel. ^aoq.-^-,OJ> 



Neither by consulting books, nor by conversing with scieriti"- 

 fic men, have I been able to arrive at clear and satisfactory 

 ideas respecting the rationale of the action of streams, in carry- 

 ing along heavy substances. The following law, however, ap- 

 pears to be supported not only by innumerable facts, but by 

 the authority of all hydraulic writers of the highest reputation, 

 viz. that, in the same channel, the increase of the depth of any 

 stream is attended by a corresponding increase of power to move 

 heavy bodies at the bottom. The Italians considered the depth 

 and perpendicular pressure of streams as the main circumstances 

 on which their action depends. Their doctrines are now con- 

 sidered as ^ploded. But the law here stated is conformable t6 

 the more modern, as well as to the more ancient theory. Miche- 



