434 Abstract of Lecture. 



PAGES 



level to fall below the theoretical curve, a parabola with horizontal axis, 

 Figs. 5 and 5A. Transverse section of Hirwain Valley, Fig. 5B, also 

 in parabolic curve, from my own survey ... ... ... 444; 445 



12. Drawing from observation of a stream at a small slope, Fig. 6. Ditto, 

 Fig. 7, of a stream with the same quantity flowing at a steeper slope, 

 showing the difference of stability or stand up of a running stream 

 represented by the difference of depth of water under the same circum- 

 stances of slope. Hitherto, slope has often been alone taken into 

 account as the cause of velocity, without calculating the quantity 

 flowing. Explanation of symbols ... ... ... ... 447> 446 



13. Different velocities of streams of different sizes show, that with about 

 twelve times the quantity flowing at the same slope, the velocity was 

 increased about two and a half times, or as the cube root of the in- 

 creased quantity. Fig. 8... ... ... ... ... ... ... 447 



14. Plan of Mississippi, showing the width at twenty-two different towns, 

 the curvilinear river course being represented by straight lines. All 

 navigable rivers decrease in width and increase in depth until they 

 approach the sea. A bar is formed by the opposing current of sand 

 or mud moved along the bottom of the river up a steep gradient (10 

 feet in a mile in the Mississippi), meeting the sand continually brought 

 up by wind waves from the sea. The opposite forces encounter at the 

 bar ; a great quantity of mud and sand overcomes the opposition, and 

 is carried along shore. Colonel Tremenheere found by experiment 

 that the material projected into the ocean by the Indus travelled 

 hundreds of miles along shore, and was found in the harbour of 

 Kurrachee. The long-shore current was often one mile per hour, and 

 continued in the same direction. Figs. 11, 12, and 13 ... ... 448 



15. Plan of Amazon, a river 2,000 miles long, with the acute angle 

 junctions of tributaries at the extremities near watersheds, and the 

 other junctions nearly rectangular. The junctions are rectangular 

 particularly when the main stream is very large, and the junctions in 

 alluvium. Fig. 14... ... ... ... ... ... ... ... 44-8 



16. Representation of the junction of the Red and other tributary rivers at 

 acute angles with the Mississippi. The great river is deflected from its 

 course by the impact of the Red River, and flows in a line, the resultant 

 of the two forces. A main river is merely the junctions between tribu- 

 taries. It has no water of its own, and its position in space is the 

 resultant of alernate and opposite forces of side streams throughout its 

 course. Fig. 13 ... ... ... ... ... ... ... ... 449 



1 7> Representation of the same streams with rectangular junctions, to show 



how absurd such an arrangement appears. Fig. 14 ... ... ... 449 



18. Law of alternate headlands and coombs (coombs are steep dry, or wet 

 valleys). These are found along every valley in the world, formed with 

 more or less regularity. The coombs and slopes are often originally 

 excavated by the water issuing from springs along the tops of the un- 

 stable and impermeable strata cropping out along the sides of the 

 valleys. The spring water dislodges the face of the stable or per- 

 meable strata, and leaves the bared edges of the rock at a steep angle, 

 which edges in the impermeable strata or clays are sloped. Fig. 15 

 represents a valley in chalk, where the strata are of uniform permea- 

 bility 450 



19. Delta of Danube, showing main stream, dividing first near the rocks of 

 Toultcha, where there are no longer any side streams or hard rocks to 

 keep the river from branching. Fig. 17 ... ... ... ... 45 1 



20. Main river deflected after receiving a branch. Fig. 16 ... ... 451 



21. Velocity in a main stream of two metres per second, shown in diagram 



