46 THE CLIMATIC FACTOE AS ILLUSTRATED IN ARID AMERICA. 



ruins of an ancient canal. Originally it appears to have been a simple ditch, but now it is 

 a mass of calcareous tufa about 3 feet wide, 4 feet thick, and hundreds of feet long. Its 

 top is grooved to a depth of about a foot, and the sides of the groove have a thickness of 

 about 6 inches. Its upper end is lost in the plain, either having been buried or eroded 

 away. The lower end disappears under a road which runs nearly parallel to the ditch. 

 Beyond the road it can not be detected and has probably been entii-ely removed by erosion. 

 The peculiar feature of the ditch is that it was not built to water the plain. If that had been 

 its purpose it would have been carried along the foot of the terrace. Instead of this it was 

 carried along the face of the terrace with as little slope as possible, so that it gradually 

 leaves the plain and approaches the top of the terrace, which, of course, has a steady slope 

 downstream. The ditch must have been designed to irrigate the top of the terrace, wliich 

 it would reach about half a mile downstream. There, as pointed out by Mr. Blazer, 

 a tract of 400 to 500 acres could be irrigated. This land is now unused, partly because it 

 is surrounded and somewhat dissected by gullies, and still more because after the bottom 

 lands have been irrigated there is not enough water left to make it worth while to build 

 a ditch to irrigate the terraces. The ditch was clearly in use for a long time, long enough 

 at least to allow the water of the spring to deposit from 2 to 4 feet of calcareous tufa. 

 Moreover, it was carefully engineered, with a slope as gentle as possible, and apparently 

 with many windings. To-day the -ndndings would almost preclude the construction of 

 such a ditch unless masonry were employed, but in the days when it was built the tributary 

 gullies had probably not been cut to such depth as now. 



The phenomena of the old canal imply conditions different from those of to-day. Two 

 possibiUties present themselves. In the first place, the bottom lands may have been 

 essentially the same as now, but the population was so dense that all this land was used 

 and more was needed. Therefore an attempt was made to utilize poorer land lying on 

 the terrace. The attempt was successful, as is evident from the thickness of the tufa, 

 which implies long use of the canal. The amount of land in question would have made 

 such an attempt well worth while. According to Mr. Blazer, the total amount would be 

 about half as much as is now under cultivation in the entire valley, including all at this 

 village and at the lower ruin, 12 miles away. The size of the canal indicates that it carried 

 approximately the same amount of water as the present stream furnishes except in times of 

 flood. The other hypothesis was suggested by Mr. Blazer as his only solution of a problem 

 on which he had pondered for years. When the canal was built, so he surmises, the valley 

 bottom, now half a mile wide, was gullied out so deeply that it could not be cultivated. 

 Possibly an alluvial plain which had formerly been cultivated had been rapidly gulhed by 

 the same process which is now beginning to destroy the present plains. At any rate the 

 ancient inhabitants were obUged to have recourse to the land at the top of the main terrace. 

 Having more skill than we generally suppose, they were able to achieve the work of making 

 the canal without tools of iron, although the difficulties due to the washing away of sections 

 of it by the sudden floods of httle tributary guUies must have been great. WTiich of these 

 two hypotheses is correct can not now be determined, nor is it essential. In either case it 

 seems probable that since man occupied the country the hydrographic conditions have 

 changed, a conclusion which agrees with the other e\ddence in showing that at least the last 

 cycle of the terrace-making process has occurred since man began to build villages and 

 practise agriculture. 



