Bowman — Geologic Relations of the Cuzoo Remains. 315 



they lie. They could not have been formed under present 

 conditions, for they are being eroded by the existing streams. 

 They were formed during a time when waste was being shed 

 from all of the higher valley heads and mountain slopes and 

 collected principally on the lower slopes. Wherever the 

 gravel deposits are traced into the higher valleys they may be 

 seen to interlock or interfinger with glacial deposits — actual 

 moraines or irregular masses of unstratitied material. The 

 interlocking relation is observable at a number of points in the 

 Cuzco basin and is, besides, one of the most common relations 

 throughout the Central Andes. I have studied similar cases 

 all the way from southern Bolivia to central Peru. Further- 

 more, the condition is widely encountered in other continents : 

 it has been noted in both North America and Europe under 

 such a variety of topographic relations that its meaning is one 

 of the clearest in physiographic geology. It would require no 

 further emphasis were it not for the great importance attach- 

 ing to it in the present instance. 



It is characteristic of glacial gravels and sands that they 

 occur in many valleys whose heads were not occupied by the 

 ice. Among this class are the deposits in the ravine in which 

 the human remains were found. It is inferred, however, that 

 they have the same age as those which exhibit an interlocking 

 relation in adjacent valleys. This appears at first sight to 

 border so closely on mere analogy, that particular attention 

 should be directed to the following argument for their age. 



Starting at the glaciated head of any of the higher valleys 

 of the Cuzco basin, one passes down over the morainic deposits 

 to the more regularly distributed and stratified alluvium of the 

 middle and lower sections of the valley. At the valley mouths 

 one looks out upon a great belt of alluvium fringing the lower 

 slopes and appearing to extend tongue-like up all the tributary 

 valleys. The plane of the surface on which one stands is coin- 

 cident with that of the surface of the adjacent deposits. There 

 is lack of continuity only where some more massive or some 

 longer spur extends far out into the basin, though such breaks 

 are rare. One can find no marked differences between the 

 deposits of the unglaciated and the glaciated valleys. In all 

 cases the material is coarse, in all cases it leads to upper rocky 

 slopes stripped bare of waste : the upper surfaces of the deposits 

 of both the glaciated and the unglaciated valleys fall into a 

 common plane : both have the same geographic position : along 

 their common border, the deposits interlock in as clear a 

 manner as do the glacial and alluvial material at the glaciated 

 valley heads : both classes are benched, showing that there has 

 been at least one important halt in the cutting down of the 

 deposits since their formation. These are not accidental con- 



