GUANO ISLANDS. 53 



the continent either by subsidence or by marine 

 erosion. Here, in the almost complete absence of 

 rain, were formed those secular accumulations de- 

 posited by sea-birds, which, when known in Europe 

 under the name oi guano, suddenly rivalled the mines 

 of the precious metals as sources of easily acquired 

 wealth. The two most considerable groups are 

 respectively named Lobos de tierra and Lobos de 

 afuera ; a smaller group near to Payta is also called 

 Lobos. At the western end of the largest of the' 

 latter group the waves have excavated a natural arch, 

 which, after a sufficient period of further excavation, 

 will fall and give rise to a new detached islet. A 

 brisk southerly breeze made the air feel cooler than it 

 had done since we entered the tropics, as we ran about 

 due south until sunset, when, after passing abreast of 

 the promontory of Ajulla, our course was altered to 

 nearly due south-east. I was assured by a native 

 passenger that the promontory of Ajulla, for a distance 

 of thirty or forty miles, is an absolute desert, without 

 a drop of water or the slightest trace of vegetation. 

 Experience has made me somewhat sceptical as to 

 statements of this nature made by non-scientific 

 observers. During the day we frequently observed a 

 fish which appears distinct from the flying-fish of the 

 Atlantic. The pectoral fins appear to be less developed, 

 and in consequence the flight is shorter, and the 

 animal seems to have less command over its move- 

 ments. 



Our course on April 14 lay rather far from land. 

 It was known that yellow fever had broken out at 

 Truxillo, and it was decided that we should run direct 



