104 



SCIENCE. 



[N. S. Vol. IV. No. 82. 



rating curves for eacli station, by means 

 of whicli tlie daily discharge can be com- 

 puted. 



In July, 1895, it was decided to expand 

 tbe work of stream measurements in tbe 

 South. Before doing so many factors en- 

 tering into the location of gauging stations 

 had to be considered. To more clearly un- 

 derstand the reasons of the location of the 

 stations established during 1895, it may be 

 well to give a brief summary of the phys- 

 ical geography of the area. 



The region under consideration may be 

 divided into four great divisions. The 

 coastal plain, extends from the coast to 

 what is known as the fall line, and consists 

 of very recent geologic formations, prin- 

 cipally sands and gravels of Cretaceous, 

 Tertiary and Post-Tertiary deposits. This 

 fall line is the eastern outcrop of the 

 old Archsen crystalline rocks of the second 

 or Piedmont division, which extends to the 

 summits of the Blue Eidge, and it also 

 marks the last considerable fall on the 

 rivers that cross it. It passes through 

 Columbus, Macon, Milledgeville and Au- 

 gusta, Ga., Columbia, S. C, Eocky Mount 

 and Weldon, JST. C, then through Eich- 

 mond and Fredericksburg, Va., crossing 

 the Potomac at Great Falls. It thence ex- 

 tends further northeastward and is finally 

 lost at the mouth of the Hudson river. In 

 the northern portion this fall line deter- 

 mines the limit of tide waters, but in the 

 Southern States as it recedes from the coast 

 it is often beyond the limit of navigation. 

 The third division of this region is the 

 greater Appalachian valley, extending from 

 the Blue Eidge to the crest of the Alle- 

 gheny front, and the fourth division is the 

 Allegheny plateau, gradually sloping down- 

 ward and westward from this latter boun- 

 dary line. The greater Appalachian val- 

 ley is a depressed zone traversed by a num- 

 ber of parallel ridges, and it is composed of 

 a variety of different kinds of rocks, as con- 



glomerates, sandstones and limestones, the 

 beds of which are tilted at various angles. 

 In the Allegheny front and to the west- 

 ward the strata are seen to be nearly par- 

 allel. 



The Piedmont section is the oldest of 

 the four divisions above noted, the rocks 

 dating from Archsean times. The Blue 

 Eidge, the western boundary of this sec- 

 tion, is the coast line of an old continent, 

 but of a continent facing westward and 

 towards an inland sea. The greater Ap- 

 palachian valley would, therefore, represent 

 the shore deposits of such a sea, and one 

 would naturally expect to find rocks diver- 

 sified in color and composition along such 

 a strip. Further to the westward or out 

 into the sea should be and are found 

 rocks of a more homogeneous character. 



In establishing the gauging stations dur- 

 ing 1894 and 1895 it has been the endeavor 

 to distribute them as much as possible in 

 these different types of areas. An impor- 

 tant consideration has been that of the 

 economic value of such stations. Wherever 

 there has been a water-power privilege de- 

 veloped, and especially when there is one 

 undeveloped on the larger rivers a gauging 

 station has been established as near such a 

 site as possible. In the accurate determi- 

 nation of the value of a water power at a 

 certain point two things should be known: 

 first, the fall at that place, which can be 

 measured once and for all; and second, the 

 variation in the discharge of the river to 

 determine which a long series of observa- 

 tions are necessary. 



It has been too often the practice to com- 

 pute the amount of water finding its way 

 into the rivers, by assuming a certain per- 

 centage of the rain falling on the area as 

 drained by the river at that point. Several 

 important factors enter into the problem of 

 run-off, beside the rate of precipitation, these 

 being the slope of the basin, the tempera- 

 ture, wind movement and the conditions 



