506 1. Bowman — A Buried Wall at Cuzco. 



quifia. The}' occur to depths of several feet, the deepest 

 burial being to a depth of about six feet. On the left-hand 

 side of the ravine the section is earth below and ash above, and 

 a bugb ash pile on which the refuse of the city is dumped still 

 persists, though its present use is far less extensive than 

 formerly. From the inclination of the alternating ash and 

 sand layers one is obliged to conclude that the ash pile existed 

 in the form of a mound from which slopes led toward the hill 

 as well as in the opposite direction on the farther side of the 

 mound. No other relation will explain the dip of ash beds 

 and sand beds toward the hill (west), at one place to the extent 

 of 28 degrees, and in many cases to 10 and 15 degrees. A 

 slight dip of several degrees could be explained by an aggrad- 

 ing stream working on all radii of an alluvial fan ; so great a 

 clip as 28 degrees seems explicable only on the assumption of 

 a mound from which ash slipjDed and was washed on gradients 

 up to the limits of repose. 



The alternating beds represent a long period of accumula- 

 tion. Only a careful study of the pottery and bone material 

 in them will establish their age, though they date back with- 

 out doubt several hundred years and the lowest may repre- 

 sent the accumulations of several thousands of years ago. 

 Wash from the adjacent hill slope is very slow indeed. Only 

 the smallest and most incipient ravines now break the smooth 

 outline of the thinly cloaked rock slope and the alluvial fringe 

 in front of it. The largest are but a foot or two deep. Under 

 present climatic conditions it would appear to require at least 

 several thousand years for the upper five or six feet of the 

 alluvial fringe to form, for it consists on the whole of fine, not 

 of coarse material, and in this respect is in contrast to the 

 coarser alluvium washed down in the glacial period by vigor- 

 ous streams, and probably in a relatively short time. 



To produce alternating ash layers on the south side of the 

 ravine would require its slopes to extend across the space now 

 occupied by the ravine. That is equivalent to saying that dur- 

 ing the accumulation of the ash and sand beds the ravine did 

 not exist. We therefore conclude that the ravine is new, 

 both from the testimony of the people and from an entirely 

 independent line of evidence, the position and relations of the 

 alternating ash and sand beds. There is a third independent 

 line of argument for the youth of the ravine ; its narrow, 

 steep-walled, fresh condition in spite of the fact that its walls 

 are merely loose sand and gravel, of all materials the most 

 likely to slump down quickly to moderate grades. If the wall 

 ever had served as part of a retaining dike on the border of a 

 ravine like the existing one, such use was abandoned long 

 before the ash beds began forming. Now if we assume a few 



