GEOLOGY OF PERU ADAMS. 415 



TERTIARY OF THE SOUTH CENTRAL COASTAL PLAIN. 



The Pisco formation. 



In the low hills to the north of Pisco, which is called " Cerro de 

 Tiza " (meaning chalk), there are exposed white and yellowish rocks 

 which have a calcareous aspect much like chalk (see pi. 4). At 

 the end of the bridge over the Pisco River they may also be seen, 

 and at this place they have steep dips and strike to the northwest. 

 This structure is continued into Cerro de Tiza, and crosses the Pisco 

 River to the south until the rocks disappear beneath the sands of 

 the plains toward lea. Many outcrops of this formation may be 

 seen, especially in the landscape to the south of the railroad station 

 at mile 18, but there the beds are practically horizontal. In the lea 

 River valley the same formation is found resting on igneous and older 

 stratified and metamorphic rocks. In a hill to the west of the 

 Hacienda Ocucaje, in a hill called " Cerro Blanco," the writer saw 

 the remains of a whale embedded in the Pisco formation. There 





Fig. 7. — Section at Paita, by Grzybowski. 



was also some strata in which a few marine shells are found and 

 others in which phosphate nodules occur, but to an extent so limited 

 that they have no commercial value. Farther south in the valley 

 of the Rio Grande the Pisco formation is cut by the canyon of that 

 river. The tributaries of the Rio Grande which flow past Palpa 

 and Nazca have cut deep valleys, in the walls of which the fonna- 

 tion is seen to contain a mixture of rounded stones in a matrix of 

 sand and clay materials, but with a sufficient amount of the white 

 chalky matter which characterizes the formation to demonstrate 

 that it is only a littoral phase of the Pisco formation. 



The Pisco formation is also found in the plains to the east of the 

 port of Lomas, where the remains of a whale were seen by the writer, 

 and in one of the valleys which cut the plain a conglomerate of ma- 

 rine shells was found. To the southward the plains narrow and the 

 mountains come to the seacoast, but at Chala there is a small area 

 of Pisco formation in which the beds consist largely of variegated 

 clays. 



In the northern part of the plains, to the east of the Caiiete, the 

 Pisco formation was found presenting a littoral phase, but containing 



