A Fault Plane of Unusual Aspect. 293 



The ledges forming the Rodadero are traversed by incipient 

 joints and broken by numerous faults of small displacement 

 along which slickensides have been developed — features com- 

 mon to both igneous and sedimentary rock masses within the 

 province of Cuzco. 



The fluted surface. 



The unusual feature of the Rodadero and the one which 

 gives it its name (Spanish, rodada, a rut), is the remarkable 

 series of polished grooves which ornament the entire surface of 

 the irregular knob (figs. 4 and 5). An area exceeding- an acre 

 is occupied by grooves whose width varies from a few inches 

 to four or five feet, and whose depth varies between a fraction 

 of an inch and four feet. Smaller flutings and delicate striae 

 traverse the troughs and crests of the larger depressions in a 

 longitudinal direction. Microscopic abrasion lines have 

 smoothed and polished the channels and ridges to such a 

 degree that one may slide down the inclines without damage to 

 clothing — an amusement indulged in by natives and tourists 

 alike ; and, if tradition is to be accepted, by the Inca rulers 

 themselves. The larger and smaller grooves are continuous 

 and parallel for 100 to 300 feet, and at one locality thirty-two 

 parallel channels with a combined width of fifty feet were 

 traced for a distance of 180 feet. About 90 per cent of the 

 grooves and ridges extend S. 30° W., but other trends are repre- 

 sented as indicated below. 



The large area exposed, the freshness and perfection of carv- 

 ing, the continuity and parallelism of the striae which give 

 this exposure a unique character, have naturally attracted the 

 attention of students of nature. Squier* described the 

 Rodadero (" La Piedra Lisa") as a rock "squeezed up in 

 plastic state between irregular and unyielding walls, and then 

 hardened into shape with a smooth and glassy surface." The 

 statement of Rivero and Yon Tschudif illustrates the extreme 

 philologic method of scientific research, and the liability of 

 being led astray by a name : " A short distance from the 

 fortress is a large piece of amphibolic rock known by the name 

 of ' the smooth rolling stone ' which served and still serves for 

 diversion to the inhabitants by rolling like a garden roller hav- 

 ing a sort of hollow formed in the middle through friction." 



Duenas, whose " Aspecto Minero del Department del Ouzco";}; 

 is worthy of high commendation," describes the Rodadero 

 as a glaciated surface, a view also held by Posnansky.§ Sivi- 



* Peru, 1877, p. 476. 



f Peruvian Antiquities, 1853, p. 249. M. E. Kivero and J. J. von Tschudi. 

 Translated into English by F. L. Hawks. 



tCuerpo de Ing. de Min. del Peru, Bol., liii. pp. 25-26, 1907. 

 §Bol. Oficina Nac. Estadist, No. 64-66, La Paz, 1911. 



