11 II. E. Gregory — A Geologic Reconnaissance 



run-off originates in this manner. The prevalence of these 

 springs in the suburbs of Cuzco indicates an abundance of 

 ground water — an undeveloped source for much-needed supplies 

 for domestic use. 



The Tullumayo, fed by concealed channels in limestone, has 

 cut a trench across the igneous mass at Sacsahuamah and drops 

 precipitously into the city, whence it is led through artificial 

 conduits to its junction with the ITuatanay. From the ancient 

 fortress to the city streets the fall of the Tullumayo is 400 feet 

 in a horizontal distance of 1,000 feet, or about 2,000 feet to 

 the mile. That the water power thus available was recognized 



Fig. S. 



~ICA 7 TTICA ANGOSTURA RUMICQOLCA 



; CUZCO 



i- 12,000 

 k 11,000 



== L- in oon 



Fig. S. Longitudinal profile of Rio Huatanay from Ttica-Ttica Pass to 

 the Rumiccolca lava field. The portion of the stream channel from 

 Huacarpay to Sierra-Bella is not shown. 



by the Spanish conquerors is indicated by the presence of an 

 abandoned mill flume. 7 



The largest stream entering the Cuzco Basin from the north 

 is Rio Cachimayo, s which rises on the glaciated, grass-covered 

 slopes of the Huatanay-Urubamba divide at an elevation of 

 13,500 feet and, after flowing for a mile along the southern 

 base of sandstone slopes forming the valley rim, cuts a canyon 

 through limestone pampas and emerges at San Sebastian. Its 

 waters are derived from marshy land at the head of the stream, 

 from rills in the sandstone ridge, but chiefly from springs 

 issuing from cracks in the limestone. The Cachimayo, partic- 

 ularly in its lower course, is heavily charged with chloride of 

 sodium, which is recovered by evaporation at the Government 

 salt works. Several small streams on the porous limestone of 

 Kkallachaca and Era pampas are perennial. In their upper 

 courses swamps and bogs are common, and definite channels 

 are usually absent. On reaching the edge of the basin the water 

 forms continuous rills occupying rock ditches and broken by 



7 The ruins of the old mill at Sacsahuaman have been ascribed to the 

 Incas, but the presence of lead cement, to which my attention was called 

 by Professor Bingham, is inconsistent with such an interpretation. 



8 The upper portion of this creek is known as Rio Lkalla-Chaca. 



