THE ROMANCE OF A RIVER 



95 



Careful measurements will soon show that 

 the level of the surface is not the same at 

 the toe-cap and over the turnpool. The 

 direct rush of water towards the outer 

 bend causes a heaping up at that place, 

 and the head of water induces a cross flow. 



Another line of inquiry is opened up 

 with regard to the activities of a stream, 

 when we consider the work it does in 

 carving out the valley in which it flows, 

 and its effect in modifying the contours 

 of the land. How can moving water, so 

 pliable and j-ielding. cut through even 

 the softest rocks ? Well, of itself it cannot, 

 unless the rocks are soluble, but it can 

 carry sand and stones in suspension or 

 roll them along its bed, and the constant 

 abrasion of the carried particles on the 

 solid rocks slowl\- but surely causes them 

 to yield. We should expect that the 

 general result of nmning water armed 

 with moving sand would be to produce 

 gorges with steep parallel sides just like 

 a vertical saw cutting into wood. That is 

 exactly what would happen if 

 the stream were the only agent 

 at work. But the effects o: 

 frost, rain, and other influences 

 are also important in the carv- 

 ing of the land, and a large 

 part of the work of disintegra- 

 tion is done by these agents. 



Their function is to widen 

 the valley and grade the sides 

 to a gentler slope. In those 

 parts of the world where rain 

 and frost are seldom met with, 

 as in Colorado, we see the effects 

 of the river action alone. The 

 wonderful cafions show exactly 

 what a river can do if left to 

 itself for long ages. But the 

 work of the river is not con- 

 fined to the breaking up of rock 

 masses. The disintegrated ma- 

 terial must be carried away and 

 deposited somewhere. In the 

 upper reaches, where the path 

 is steep and the current rapid, 

 large boulders maybe carried. It 

 seems almost incredible that the 

 tiny stream we see under ordinary 

 circumstances should be capable 

 of moving such large stones. In 

 some mountain streams certain 

 boulders have been marked and 



their positions carefullv ascertained. Ob- 

 servations made year after year show that 

 the marked boulders do move, and their 

 rate of movement has been determined. 



When it reaches the plain the current 

 is sluggish and only capable of trans- 

 porting the finer materials. There is a 

 beautiful and delicate adjustment between 

 the current and the material carried. 

 The balance is disturbed in times of 

 flood and excessive drought, but when 

 these abnormal phases have passed, the 

 stream adjusts itself once more and 

 returns to a state of equilibrium. 



We have now followed our type stream 

 from the hills to the plains ; there is still 

 another part of a stream where it empties 

 itself into the sea. Long before reaching 

 this stage our little brook has joined its 

 waters with others to form a large river, 

 and the estuary can best be discussed 

 when we pass in review some of the 

 characteristics of larger examples. 



J. LOM.AS. 



"IT SEHMS ALMOST INCKKDI lU.l ; THAT TIIK TINY 

 STREAM SHOULD BK CAPABLE OF MOVING 

 SUCH LARGE STONES.' 



