45° 



Law of alternate Coombes and Headlands. 



Fig. 14A represents the Amazon. The junctions in the mountains are at 

 acute angles, but near the mouth aimost at right angles, as in all rivers. 



(18) Fig. 1 $ is a drawing of the alternate headlands and coombes observed 

 on the sides of every valley in the world. 



HORIZONTAL LINE 



Fig. 17 gives a plan of the Delta of the Danube, from the works of Sir C. 

 Hartley. I give it merely to show that the cause of a river forming a delta 

 is, that there is no longer in its course any tributary streams to keep the river 

 in one channel by equal and opposite actions, from the brooks and rivers falling 

 into the valley from alternate sides. Thisisthecase in all large rivers having deltas. 



Fig. 16. The line F C is the exact resultant of the unequal forces coming 

 from F F and C A. 



Fig. 16 shows the effect of a tributary in changing the line of the main 

 stream, which is the exact resultant of the forces if between the two streams 

 joining, allowing for the respective differences of slope and quantity flowing in 

 each tributary. If the tributary joined at 45 and was -^ the volume of the 

 main river, it would deflect the main stream one degree. 



Thus valleys are deflected from their direction, at the junction of tributary 

 valleys. If the area drained by a great river is of symmetrical form, the river 

 will occupy the medial line, and be the resultant of the alternate and opposite 

 forces of tributaries coming in on the opposite sides of the valley the main 

 stream occupies. 



Fig. 18 is a case giving the effect on velocity in relation to different quantities 

 flowing, by diverting a large channel into three channels, one twice as large as 

 the other two. If the Nile was artificially divided higher up than at present, 

 the current in the three streams would be much slower than at present, and the 

 rise of river earlier and higher. If the Rhine was prevented from dividing, it would 

 flow out to sea in a good stream, so as to keep a passage open for large ships. 



From what has been seen in Fig. 8 and in other diagrams, although all these 

 streams are at the same slopes, the mean velocity of the single stream before 

 it divides will be greater than either of the others ; and the mean velocity of 

 the larger stream of the three will be greater than the two small ones, although 



