'jlic Study of River Ccology, 2^ 



in^e^ the average slope of the surface, which, if you are not pre- 

 pared to take it for yourself, may be determined apjoroximately 

 from the various railroad surveys in the region. 



Note, also, the general character of the soil in the country 

 drained and of the material through which the stream has made 

 its bed, whether rocky, sandy or clayey, for upon these things 

 will depend its power of cutting down or eroding the land sur- 

 face, and upon this erosive power of river systems are based 

 many of the estimates of the length of time necessary for the ac- 

 cumulation of sedimentary rocks. 



You will also determine the velocity of the stream and the 

 weight of the sediment which is deposed from a stated amount 

 of water at various stages and at different times of the year, both 

 from simple mechanical suspension when the water is dipped up 

 and the foreign matter allowed to settle, and from solution upon 

 evaporation. By determining the velocity of the stream, its 

 width and mean depth at any point, you can estimate, at least 

 roughly, the amount of water which will pass this point in any 

 given time, and by ascertaining the amount of solid matter 

 carried in each gallon of water you will know approximately the 

 amount ot matter carried by the entire stream, and from this, if 

 you know the area of the surface drained by the stream you are 

 studying, you can tind the average depth to which this general 

 land surface has been eroded during, say, the past year, or last 

 century. 



Of course these estimates should only be based upon observa- 

 tions made at various times of the year, as the amount of water, 

 velocity and consequently the amount of matter carried will vary 

 greatly with the seasons. 



Study the extent and character of the flood-plain and notice if 

 there are terraces or other evidences of the former action 

 of the stream at higher levels, and if you find such deposits, 

 note the physical character of each, as compared with the others, 

 and if you find in them remains of plants or animals; determine 

 whether they belong to recent species or not, and if you are near 

 the coast, whether such species are marine or fresh- water. 



You will also find it a matter of much interest to note the way 

 in which sand-bars are formed under the influence of the currents, 

 especially where there is a bend in the stream, in which case the 

 velocity of the current and the angle of the bend should be noted 

 in connection with the character of the bars formed. 



When bends occur, bars will be formed on the inside of the 

 curve, while the opposite bank will be cut away. 



Then where a tributary stream flows into the main one, you 

 will study the character of the bed and the way in which sedi- 

 ments are deposited, and lastly, going into the mathematics of 

 geology, you will be much interested m studying the law of trans- 



