GEOLOGY OF PEKU ADAMS. 409 



hill above the town of Cuzco, and expressed his opinion that the 

 whole valley in which Cuzco lies was occupied by a glacier. The 

 evidence given for so great a glacier is not quite so complete as 

 might be wished, at least its lowest limit should be determined. Ac- 

 cording to Dueilas the elevation of the Eodadero is 3,900 meters ; the 

 present limit of perpetual snow in that region is at 4,300 meters, and 

 Cuzco is at 3,450 meters. 



Undoubtedly the limit of perpetual snow was much lower during 

 the glacial period. Just how much lower, is a question deserving of 

 study. Raimondi has noted (1873) the occurrence of moraines much 

 below the present snow line in the Cordillera Blanca. 



At many places near the snow fields abandoned cirques may be 

 seen below the limits of the perpetual snow and the diminutive 

 glaciers of the present time. The writer has studied the glacier 

 beds and moraines in the vicinity of Poto to the north of Lake 

 Titicaca in the Cordillera Oriental and has estimated that in the 

 glacial period the ice fields extended about 2,500 feet lower than the 

 present glaciers." 



Recent elevation of the coast. 



Obebvations at San Lobenzo Island by Dabwin. 



In 1835 Darwin visited Peru and landed at Callao, but because of 

 the troubled political condition he saw but little of the country. He 

 reported finding on San Lorenzo Island, in front of the bay, three 

 obscure terraces, the lower one of which, at a height of 85 feet above 

 the sea, is covered by a bed a mile in length almost wholly composed 

 of shells of 18 species now living in the adjoining sea. He found a 

 bed of more weathered shells at an elevation of 170 feet. Among the 

 shells at 85 feet above the sea he found some thread, plaited rushes, 

 and the head of a stalk of Indian corn. From these facts he con- 

 cludes that within the Indo-human period there has been an elevation 

 of 85 feet. [These observations by Darwin have been often quoted, 

 and only last year an excursion composed of professors and students 

 from the School of Mines at Lima visited the island to study these 

 terraces, and failed to reach a definite opinion in regard to the value 

 of Darwin's conclusions.] 



Observations at San Lorenzo Island by Dana. 



Fortunatel}'^, the views of Darwin have been competently criticized 

 by Dana, who (1840) visited tlie locality as a member of the Wilkes 



"In northern Bolivia Artliur F. Wendt lias observed that the glaciers of 

 Illimani and Sorata have their low^er termination at an elevation of about 

 18,000 feet, and that the ancient glaciers reached down to 15,000 feet. (Proc. 

 Amer. Inst. Mining Eng., 1890, vol. 19, p. 85.) Agassiz (1868), It vpill be 

 remembered, regarded the clays and superficial deposits of the Amazon Valley 

 as glacial deposits, but later recognized his error, 



