496 A NATURALIST IN THE PACIFIC chap. 



Evidence of a more direct nature could doubtless be supplied 

 by those who have long resided on the coast of Ecuador, and in 

 illustration I will give an extract from one of Mr. Walker's letters 

 dated May, 1904, from Santa Elena. — "The rainfall here might for 

 the last ten years be put down at two showers per year. It is said 

 that the last good rainy season was in 1891. The inhabitants say 

 that formerly it always rained enough to make the grass grow 

 every year, but during the eleven years I have been here there 

 appears to be a marked falling off of the rainfall." 



It has been only possible to touch the fringe of this inte- 

 resting question here ; but from the standpoint of the study of the 

 littoral flora of the west coast of South America it is of some 

 importance. Immediately behind the epoch of the present marine 

 molluscan fauna of this coast there lies an age when, as we learn 

 from Philippi, the shells of Chile were more akin to those of the 

 Atlantic and Mediterranean faunas than to those now found on the 

 Chilian coasts. The transition is a sudden one; and amongst 

 other explanations of this strange transformation Suess suggests 

 the sealing up of a communication through the Panama isthmus 

 by volcanic eruptions and the appearance of the Humboldt 

 current (^Das Antlitz der Erde, French edit, by Margerie, ii. 825). 

 May it not be, my readers may ask, that the west coast of South 

 America is still in the age of progressive sterility ; and that before 

 this age began Peru possessed a normal tropical strand-flora ? It 

 has been remarked in Chapter VIII. that the same species of 

 mangroves occur on both the Atlantic and Pacific coasts of 

 America, and that at all events their present distribution belongs 

 to an age when the Gulf of Mexico was in communication with the 

 Pacific Ocean. May we not, again, suppose that in that age the 

 mangroves extended far south on the coast of Peru, just as they do 

 now on the coast of Brazil ? 



Coral reefs are stated not to exist in tropical latitudes on the 

 west coast of South America in our own day ; but we might 

 almost expect that at the close of the Tertiary period, and perhaps 

 before the appearance of the Humboldt current, they existed with 

 the mangroves on the coast of Peru. As bearing on the subject of 

 a change of climate on that coast in times geologically not remote, 

 I may allude to the circumstance, which is discussed more in detail 

 in Note 75, that I found, sometimes in fair quantity, blocks of 

 massive coral, long since dead, much pierced by boring shells, and 

 in places undergoing a chemical change, at Arica (lat. 18° 25' S.), 

 at Callao (12" 3' S.), and at Ancon (11° 45' S.) on the coast of Peru. 



