312 



FORESTRY AND IRRIGATION 



July 



tions represented by these two streams 

 may then be roughly stated as fol- 

 lows : 



i. The slope of the Esopus basins 

 are twice as steep as those of the Wall- 

 kill. 



2. The fall of the Esopus is six 

 times as rapid as that of the Wallkill. 



3. The topography of the Esopus 

 basin is much more simple and direct 

 than that of the Wallkill. 



4. The Esopus has no natural reser- 

 voirs, whereas a relatively large per- 

 centage of the Wallkill basin consists 



o 



of swamps and ponds. 



With regard to the bearing of these 

 factors upon stream flow, it is evident 

 that in each of these four important 

 respects, the conditions upon the Wall- 

 kill basin are much more favorable to 

 underground seepage and equable 

 stream flow than on the Esopus basin. 

 As pointed out in the general dis- 

 cussion of this subject, steep slopes 

 such as those of the Esopus favor the 

 immediate discharge of precipitation 

 as surface run-off with but little 

 underground seepage, while moderate 

 slopes such as those of the Wallkill 

 favor the slow and gradual discharge 

 of precipitation with a maximum of 

 underground seepage. A steep chan- 

 nel and simple, direct topography like 

 that of the Esopus accelerate the dis- 

 charge of flood waters from all parts 

 of the drainage basin, causing sud- 

 den and rapid fluctuations in the flow 

 of the main stream, while a channel 

 of very moderate grade and winding, 

 indirect tributary streams, like those 

 of the Wallkill, have an exactly op- 

 posite effect. Of great importance 

 also is the natural storage of flood 

 water in swamps and ponds which we 

 find in such marked degree on the 

 Wallkill basin and which is lacking 

 entirely in the basin of the Esopus. 

 In all four respects, therefore, the 

 Wallkill has a marked advantage over 

 the Esopus in the natural conditions 

 favoring evenness of stream flow. As 

 far as the single factor of topography 

 is concerned we would expect the 

 Wallkill River to be much more reg- 



ular in its behavior than the Esopus 

 Creek. If this is not the case, it must 

 clearly be due to the counter influence 

 of some other factor governing stream 

 flow. 



4. The fourth factor with respect 

 to which the two catchment areas are 

 to be compared is that of geology. 

 Of the Wallkill basin, fully 80 per 

 cent, consists of Hudson River slates 

 and corniferous limestones. The slate 

 is moderately soft and resistant, ap- 

 proaching often a fine, flaky shale in 

 texture. It forms as a rule the hills 

 and low secondary divides of the 

 basin. The limestone which is as- 

 sociated everywhere with the slate, 

 forming usually the immediate basins 

 of the streams, is soft, porous, and 

 non-resistant to erosion. 



These rocks have formed by disin- 

 tegration deep layers of fine loamy 

 and marly soils, supplying the basin 

 with an excellent surface for absorb- 

 ing precipitation and converting it into 

 underground seepage. The large areas 

 of soft, porous limestone, moreover, 

 would tend to absorb directly large 

 quantities of water, either storing it 

 and yielding it up gradually to the 

 surface, or allowing it to percolate 

 through into underground water 

 courses and channels of spring sup- 

 ply. 



Of the Esopus basin, on the other 

 hand, 90 per cent, consists of thick 

 beds of sandstones, shales, and flags 

 of the Catskill and Hamilton forma- 

 tions. In general these rocks are 

 dense in texture, coarse grained, hard, 

 and resistant to erosion. Their hard, 

 resistant character is shown by the 

 vertical cuts, sheer ledges and gen- 

 erally rough topography of the Esopus 

 basin. The character of the mother 

 rock, combined with the steepness of 

 the mountain slopes, has resulted in 

 the formation of a very thin layer of 

 soil, the rock being at best scantly 

 covered and in many cases entirely 

 exposed. Not only is the absorbing 

 layer of soil which plays such an im- 

 portant part in the storage of precip- 

 itation verv thin over much of this 



