so NOTES OF A NATURALIST. 



mountains varying from four to six hundred miles 

 in width, and can carry no moisture available to pro- 

 duce rain on the western seaboard. In Ecuador the 

 two principal ranges— the Cordillera and the Andes — 

 are much nearer together than they usually are in 

 Peru, and no parallel ranges flank them on the east 

 The numerous tributaries of the Maranon flow in a 

 tolerably direct course east or south-east, many of 

 them rising within a hundred and fifty miles of the 

 Pacific coast. It follows that the atmospheric currents 

 meeting less preliminary obstruction reach the eastern 

 slopes of the main range still very heavily charged 

 with vapour. In crossing the barrier a large portion 

 of the burthen must be deposited ; but it is probable 

 that a large amount is nevertheless carried to the 

 western side of the range. 



It may be said that this explanation, whatever it 

 may be worth, cannot apply to the territory of 

 Colombia, where the Andes are broken up into at 

 least three lofty ranges, and the mountains cover as 

 wide a space as they do in Peru. My impression is 

 that the abundant supply of moisture on the west 

 coast of Colombia arises from a different source. The 

 effects of the Isthmus of Panama as a barrier against 

 atmospheric currents must be absolutely insignificant, 

 and I have no doubt that those which flow eastward 

 along the coast of the Caribbean Sea are in part 

 diverted south-east and south along the west coast of 

 Colombia. 



There can, however, be little doubt that in deter- 

 mining the climate of the west coast the influence 

 of the Humboldt current, and of the cool southerly 



