306 Bowman — Geologic Relations of the Cuzco Remains. 



Art. XXVII. — (Part II) The Geologic Relations of the Cuzco 

 Remains /* by Isaiah Bowman. 



Historic Cuzco lies at the head of one of the most beautiful 

 in termon tane valley-basins in the Central Andes. The broad 

 flat basin floor is deeply cloaked with land waste which also 

 extends well up the bordering slopes and the tributary valleys. 

 High mountains rim about the basin like a gigantic wall and 

 their slopes in a few places lead up to summits snow-covered 

 during the southern winter. The upper grass-covered slopes 

 are the home of mountain shepherds who find in the other- 

 wise unoccupied lands of their bleak territory ample room 

 for their flocks and herds. Upon the lower slopes of the 

 mountains the agricultural Indian breaks a touoli sod here and 

 there and plants his chief vegetable, the potato. Farther 

 down, on the fringe of alluvium, are grain fields, potato 

 patches, and bright green alfalfa meadows — almost all irrigated 

 land, intensively cultivated, and supporting a dense popula- 

 tion. 



The Cuzco basin (fig. 1) is about fifteen miles long. Its 

 width varies from a few hundred yards at the narrow lower 

 outlet of the basin to several miles a little below Cuzco. The 

 floor of the basin is from 11,000 to 11,500 feet above sea level. 

 Dozens of small streams rising in the surrounding highlands 

 follow steep irregular courses and furnish water to the irriga- 

 tion ditches. Among these the Huatanay and the Tulumayu are 

 the most important. All of these streams bear down quantities 

 of land waste (now much less than formerly) and all have dis- 

 sected the marginal belt of alluvium and even the alluvial floor 

 of the basin, which they formerly built up. Therefore at some 

 time in the recent geologic past the streams of the basin have 

 changed from aggrading to degrading agents. 



It is in one of the ravines cut into the bordering alluvium that 

 the gravel deposits are exposed in which the Cuzco man was 

 found.* The present city extends up to the mouth of the 

 ravine as shown in fig. 4. The lower ravine appears to have 

 been occupied by man for a long time. Several feet from the 

 surface and interstratifiecl with the surface material are artificial 

 beds of wood ashes alternating with thin yellowish-brown lay- 

 ers of sand and gravel. It appears that when the present 

 slopes were being fashioned, and before erosion had gashed the 

 alluvium, man inhabited the region and that he has witnessed 



- I am indebted to Professors Schuchert, Gregory, Barrell, Lull, and 

 MacCurdy, for criticisms. 



f For an account of the discovery by Professor Bingham see the preceding 

 paper. 



