292 E. E. Gregory — The Rodadero (Cuzco, Peru J, — 



texture ; but even in the freshest hand specimens black crystals 

 of augite and minute clusters of epidote may be differentiated 

 from the denser groundmass, thus giving the rock a porphy- 

 ritic appearance. Petrographic analysis of the Rodadero rock, 

 described by Sqnier* as "amphibolic rock" and again as 

 " trachytic rock," by Markhamf as " limestone," and by Duenas^: 

 as " altered diabase," revealed the following constituents : 

 Well-preserved crystals of augite, fresh or kaolinized plagio- 



Fig. 3. 



?-ZJ**&> 



"-y. 'V;-.V-~' ' 



Fig. 3. Incaic wall in Calle del Triunfo, Cuzco, built of rock identical 

 with that forming the Kocladero (A. H. Bumstead, photo.). 



clase feldspars near andesine in composition, chlorite probably 

 representing biotite and hornblende, apatite and iron grains in 

 very small amounts ; epidote occurs abundantly distributed as 

 grains and clusters. The rock forming the Rodadero may 

 therefore be classed as an augite diorite porphyry. 



Rock of this type taken from the quarries adjoining the 

 city was highly prized by the architects of the Inca dynasty, in 

 spite of the labor and skill involved in working the resistant 

 material. The best preserved walls of ancient Cuzco, for 

 example those bounding Calle del Triunfo (fig. 3), in which 

 the stones are fitted and polished with wonderful skill, are built 

 of this material. 



* Peru : Incidents of travel and exploration in the land of thelncas, 1877, 

 pp. 468 and 476. 



f Cuzco : A Journey to the Ancient Capital of Peru, 1856, p. 115. 

 JCuerpo de Ing. de Min. del Peru, Bol., liii, p. 179. 



