494 A NATURALIST IN THE PACIFIC chap. 



ture much cooler than the lower coast regions ; and the air-currents 

 do not precipitate any moisture on the land until an elevation of 

 4,000 to 6,000 feet is attained where the cloud-belt is formed. 



In order to establish this theory it is, however, necessary to 

 show that when the Humboldt current leaves the coast normal 

 conditions of humidity occur, to which the vegetation responds, 

 and that when the current strikes the coast again the con- 

 ditions of aridity reappear. In its course northward the current 

 divides ofT Cape Blanco, the principal mass of its waters making 

 towards the Galapagos Group, whilst the remainder, after crossing 

 the Gulf of Guayaquil, flow along the coast of Ecuador between 

 Santa Elena and the equator. Now, it is along this stretch of the 

 Ecuador coast that the conditions of aridity reappear and that the 

 climate of the Peruvian sea-border is in a modified form repro- 

 duced. In the interior of the Gulf of Guayaquil, on the other 

 hand, where the sea-border is no longer subjected to the influence 

 of the cold waters of the Humboldt current, the genius of the tropics, 

 repressed through so many degrees of latitude, bursts its bonds, and 

 presents us with a spectacle of littoral vegetation that, so far as 

 mangrove-growth is concerned, is probably unrivalled on our 

 globe. 



This contrast is well shown in the mean annual temperatures 

 on the opposite sides of the Gulf of Guayaquil. Baron von Eggers, 

 quoting Dr. Wolff, states that whilst the mean for the year at Puna 

 is about 75° F., and at Santa Elena about 73", on the south side of 

 the gulf at Balao it is several degrees warmer and is evidently not 

 under 80°. The mean temperature for the second week of March 

 during my sojourn at Puerto Bolivar, which is near the beginning 

 of the mangrove region on the south side of the gulf, was 79°, the 

 mean daily range being 74° to 83-5°. This stretch of dry coast 

 reaching north from Puna to the equatoi is evidently regarded by 

 Baron von Eggers and others who have studied the climatology of 

 Ecuador as the critical area required to confirm the theory con- 

 necting the aridity of the west coast of South America with the 

 Humboldt current. Here the sea for the greater part of the year 

 has a temperature (according to the British Admiralty chart of 

 surface-temperatures) of 70° to 75° ; the mean temperature of the air 

 is 73° to 75° ; the rainy season, instead of covering a period of six 

 months and over, as in the humid regions north and south of this 

 coast, has a duration of only two or three months ; the prevail- 

 ing wind is south-west; whilst the direct influence of the cool 

 waters of the current is shown in the general cloudiness that 



