No. 13. — Recent Corals from Tilibiche, Peru, by Alexander 

 Agassiz and L. F. Pourtales. 



The corals described here by Mr. Pourtales were collected in a 

 ravine about two miles east of Tilibiche, in the valley of Berenguela. 

 Tilibiche is on the northern edge of the Nitrate Basin to the rear of 

 Pisagua, Peru. These corals are interesting, coming as they do from a 

 height of 2,900 to 3,000 feet above the level of the sea, at a distance 

 in n straight line from the Pacific Ocean of twenty miles. The ra- 

 vine where they were found is about 450 feet below the general level 

 of the great Nitrate Basin of Peru, on the eastern side of the ridge, 

 parallel to the coast which divides the so-called Pampa de Tamarugal 

 from the lower narrow pampas extending from the summit of the 

 coast terrace (at a height of about 1,100 feet) to its western base. 

 The height of the base of the second parallel chain ranging from 

 2,500 to 3,000 feet. The river flowing through the valley of Be- 

 renguela has cut a deep canon not only through the comparatively 

 soft deposits underlying the Nitrate Basin, but also through the 

 Jurassic beds which constitute the greater part of the chain form- 

 ing the eastern edge of the Nitrate Basin. The corals were found 

 attached to the surface of the rocks in the interstices between adjoin- 

 ing masses, growing much as they would at the present day in similar 

 circumstances. 



From the general features of the country along the Pacific coast 

 of Peru it requires but little imagination to reconstruct the former 

 internal sea formed by the Coast Range, which must have, within 

 comparatively recent geological times, covered the whole of the Ni- 

 trate Basin, and which has gradually been elevated to its present 

 position. At one time (the older period) this inland sea was con- 

 nected with the Pacific through the breaks of the Coast Range form- 

 ing the quebradas of Vitor, Camarones, Pisagua, Loa, etc., and 

 subsequently became an inland salt lake disconnected from the 

 Pacific, to be eventually drained by the breaking through of the 

 barriers at the old points of connection with the Pacific. This inland 

 salt lake was thus gradually changed to a lagoon, and finally entirely 

 drained as soon as the rivers flowing through it, forming the above- 



