Mabch 12, 1909] 



SCIENCE 



419 



in terms of the gradient of the river. The 

 Mississippi has a gradient of a few inches per 

 mile from Cairo to the gulf; while the 

 Amazon, rapidly aggrading its flood plain and 

 still quite under the domiaion of the waste 

 delivered to it, has, according to the best baro- 

 metric determinations, an average gradient for 

 the last 500 miles of only one eighth of an 

 inch per mUe !^ Barometic determiuations are 

 notably unreliable, but errors are at a mini- 

 mum near sea level in the tropics and this 

 value may be taken as indicative of at least 

 the order of magnitude of the river gradient. 

 The Nile has now been carefully measured 

 by an almost complete line of leveling from 

 Victoria Nyanza to the Mediterranean, a dis- 

 tance of 3,500 miles. It offers a similar set of 

 conditions in its flattest part between Sorbat 

 and "Khartum, where the slope has been reliably 

 determined to be from one half to one third 

 of an inch per mile.' More striking is the 

 statement of elevation in terms of channel 

 bottom : " the bottom of the channel of the 

 Mississippi is as much as 100 feet below the 

 level of the gulf some 20 miles above New 

 Orleans."' 



It occurred to the writers that in the case of 

 the Mississippi a possibly still more striking 

 form of expression is that which refers the 

 elevations of channel bottom to sea level, thus 

 arriving at an upstream point where the plane 

 of sea level intersects the channel bottom. 

 The distance of this intersection from the sea 

 or the river mouth is a very striking value 

 indeed. The detailed results of our map ex- 

 amination are expressed in the following table 

 which is compiled from the charts of the 

 Mississippi River Commission based on the 

 surveys of the period 18Y9-1884. The table 

 shows the maximum depressions and eleva- 

 tions of the channel bottom that occur on each 



■Colonel G. E. Church, "South America: An 

 Outline of it3 Physical (Jeography," Creog. Joum., 

 Vol. 17, 1901, p. 382. 



"Reported in a paper on the longitudinal aeo- 

 tion of the river delivered at the 1908 meeting of 

 the British Association and noted in Nature, 

 October 15, 1908, p. 617. 



• Chamberlain and Salisbury, " Geology," Vol. 

 1, p. 162. 



chart, the location of each point (referred to 

 a station usually near some town or land- 

 ing), together with its distance from the gulf. 

 It will be observed that the first upstream 

 point at which the channel bottom attains gulf 

 level is 388 miles by river from the guK. The 

 most northerly point at which the bottom 



1 mile below Lake St. John Landing 



1 mile below Giles Landing 



7 miles below Coles Creek Landing 



2 miles below Coles Creek Landing 



3 miles below Buena Vista Landing 

 6 miles above Buena Vista Landing 



2 miles above St. Joseph 

 1 mile below St. Joseph 



1 mile below Grand Gulf Landing 

 10 miles above Grand Gulf Landing 



2 miles above New Town Landing 



6 miles below New Town Landing 



2 miles above Warrentown 



4 miles above Warrentown 



4 miles below Vicksburg 

 1 mile below Vicksburg 



5.5 miles below Milliken's Bend Landing 

 1 mile above Milliken's Bend Landing 



4 miles above Villa Vista Landing 

 At Villa Vista Landing 



7 miles below Arcadia Landing 



4 miles below Arcadia Landing 



1 mile below Shepard Landing 

 1 mile above Shepard Landing 



6 miles above Nelson Point Landing 

 0.5 mile above Nelson Point Landing 



0.5 mile above Carolina Landing 



5 miles below Carolina Landing 



2.5miles above Lake Washington Landing 

 4 miles below Lake Washington Landing 



occurs at ^If level is 181 miles farther up 

 the river, or 569 miles from the gulf I Here 

 in a narrow and extremely sharp bend the 

 channel reaches a depth of 135 feet, or more 

 than the elevation of the surface of the stream 

 above gulf level at this point. 



Isaiah Bowman 

 C. F. Graham 

 Yale Univeesity 



•Elevations have been referred to sea level by 

 computations based on the relation of the datum 

 plane for each sheet to gulf level at Biloxi, Mia3. 



