President's Address. 55 



If now we Iiave a stream that rises in a mountainous district and 

 flows across a plains area, and untimately enters the ocean, we have 

 such a variety of surface inclinations that complications are set up. 

 When the terrific rains come in the mountains the streams with 

 high declivity assume the proportions of mountain torrents and 

 the carrying power of the water becomes so enormously great that 

 mud and silt and sand, gravel and boulders, all together are hurled 

 downward as though they were mere toys. Few can appreciate the 

 limit of such power. I have seen boulders, egg-shaped in propor- 

 tion, more than twenty feet in diameter, weighing doubtless more 

 than a hundred tons, which have been carried along by these moun- 

 tain torrents; and as they went bumping the bottoms and the sides 

 of the channel they produced wonderful execution. The same 

 stream of water, however, cannot have this high velocity forever, 

 and as the plains region is reached the angle of declivity is reduced, 

 the velocity correspondingly is retarded, the carrying power is much 

 more reduced and the unloading .process is necessary. The first ob- 

 jects to be unloaded, of course, will be the largest ones. The force 

 of the water against a boulder, or a gravel, or a grain of sand, is 

 proportional to one-half the surface of the object, which, in turn, 

 is proportional to the square of the diameter, while the weight is 

 proportional to the volume, and that in turn proportional to the 

 cube of the diameter. Therefore, the largest objects will be dropped 

 first. 



Visit a mountain stream whenever you may and you will find 

 the boulders accumulating where the first check in the velocity of 

 the current was brought about. If the decrease in velocity is suf- 

 ficiently great, sand and mud will be intermingled with the boul- 

 ders, but if the decrease is limited, then we find the boulders 

 washed clean, the finer particles having been carried farther along. 

 I need only revert to such streams as the Rio Grande, rising in the 

 mountains above Albuquerque; the Arkansas, rising in the vicinity 

 of Cripple Creek; the Potomac, rising on the summit of the Ap- 

 palachians, or any one of the many other streams known to all. 

 AVhere the angle in the surface is greatest there the most unload- 

 ing occurs. 



This unloading sometimes reaches enormous proportions, and 

 the river builds up its channel until in extreme cases it is hun- 

 dreds of feet above the plains on either side. Of course, such con- 

 ditions cannot exist long, and sooner or later the water of the river 

 will overflow its bounds and will get down onto the lower grounds 

 on the right hand or the left, only to build up another channel. In 



