452 



SCIENCE 



[N. S. Vol. XLVII. No. 1219 



Cattle make trails along the line of easiest 

 passage, usually the center of a canon. They 

 differ from the wild animals in that they are 

 not hmited by man and must not shim narrow 

 confined places, but actually converge toward 

 them. Their trails grow rapidly and the 

 writer can recall many which are five feet 

 ■wide and a foot and a half deep. These 

 trails effect erosion in two ways. First they 

 form channels for the passage of water; 

 second because of the absence of vegetation 

 they form channels of easy erosion. Their 

 compact surfaces are also hard places for 

 the water to sink into the soil. During a 

 heavy shower it is noticeable that water starts 

 to form pools in these trails long before the 

 surrounding surface shows the slightest sign 

 of having reached its saturation point. When 

 the storm becomes heavy each one becomes a 

 miniature torrent and rapid erosion takes 

 place in much the same manner as it does 

 on a steep country road and finally small 

 gullies are worn. Where rounded gullies are 

 already present the walls are broken down 

 and the vertical-walled arroyo finally results. 



The influence of cattle on the vegetation of 

 canon bottoms as a whole is rather difficult 

 to estimate, yet it must be considerable. The 

 writer has seen in canon pockets inaccessible 

 to cattle deep grass so matted and tangled as 

 to preclude any thought of erosion and cause 

 maximum absorption, while in the same canon 

 where the cattle have ranged, the bottom is 

 nothing but a tramped field of dust which 

 offers maximum opportunity for erosion and 

 minimum opportunities for absorption. This 

 is particularly true in the mid summer and 

 autumn months when cloud-bursts are fre- 

 quent. We may, therefore, summarize the 

 effect of cattle by saying that they increase 

 the rapidity of the run-off and the rate of 

 erosion by destroying vegetation, by com- 

 pacting the soil and forming channels for the 

 passage of water. 



The introduction of this new element 

 produced a disturbance in the nicely balanced 

 forces of erosion so that the alluvial flats of 

 the caiion bottoms were no longer planes of 

 equilibrium. The increased volimies of water 



that swept down the canons demanded larger 

 channels. These the trails and the small 

 gullies which grew from the trails, sup- 

 plied, until finally the process formed the 

 arroyos we meet to-day. The present cycle 

 is one of readjustment. In wide caiions the 

 alluvium will be cut away until the width of 

 the stream course becomes so great that water 

 wil lack the force to erode and the final channel 

 will be a rounded one of somewhat lower 

 grade and much closer to bed rock than the 

 present one. In narrow canons the alluvitim 

 will be entirely removed (along Chaquaqua 

 Creek this has already taken place) and the 

 stream erosion grade will be formed. Of 

 course this process is small by the side of 

 the great base leveling which is taking place 

 in these regions, but it is interesting in that 

 it shows the extreme nicety with which the 

 forces that erode are balanced. It also shows 

 rather forcibly one of the effects of the in- 

 fluences of human industry on the topography. 

 Its economic effect is not as great as that of 

 deforestation, but it will result in the ulti- 

 mate abandonment of many small farms along 

 some of the streams. For these reasons it is 

 deserving of further investigation. 



James Terry Duce 

 Universitt or Colorado 



AN EMERGENCY SUPPLY OF RUBBER 



The department of botany of the University 

 of California has undertaken a study of certain 

 West American shrubs belonging to Chryso- 

 thamnus and other genera of the Compositas to 

 determine whether or not an emergency or 

 supplementary supply of rubber exists in such 

 native plants. This investigation is one of the 

 projects of the botanical subcommittee of the 

 Pacific Coast Research Conference acting under 

 the Council of Defense of the State of Cali- 

 fornia. Results thus far obtained indicate that 

 the total amount of rubber present in these 

 native species is considerable, but that the per- 

 centage yield of individual plants is too small 

 to render its extraction profitable at present 

 prices. If, however, the imjwrtation of raw 

 rubber should be curtailed through enemy 

 action, this emergency supply existing within 



