52 NOTES OF A NATURALIST. 



light may be thrown upon the matter by a scientific 

 traveller able to spare the necessary time. So far as 

 I know, no such abrupt and complete a change is 

 known elsewhere in the world. I was unable to 

 obtain any information as to a range of hills or moun- 

 tains, marked in Arrowsmith's map " Sa. Amatapi," 

 which appears to extend east or east-north-east from 

 Cape Parinas. Its height can scarcely be considerable, 

 as it does not appear to have attracted the attention 

 of the seamen who are familiar with this coast ; but, 

 on the other hand, there is some reason to think that 

 the southerly breezes prevailing on the coast do not 

 extend to any great height above the sea-level. It 

 would be interesting if we should find on the opposite 

 sides of a range of unimportant hills the same con- 

 trasts of climate and vegetation that are known to 

 prevail between the eastern and western slopes of the 

 Peruvian Andes.* 



Along the coast of Northern Peru are numerous 

 small islets, evidently at some period detached from 



* The abrupt change in the vegetation on this part of the American 

 coast has been noticed by Humboldt, Weddell, and other scientific 

 travellers. In a note to the French edition of Grisebach (" Vegetation 

 du Globe," traduit par P. de Tchihatcheff, ii. p. 615), M. Andre expresses 

 the opinion that this, as well as some other cases of abrupt change 

 in the vegetation observed by him in Colombia, are to be explained by 

 the nature of the soil, which in the arid tracts is sandy or stony, and 

 fails to retain moisture. Admitting that in certain cases this may 

 afford a partial explanation of the facts, it is scarcely conceivable that 

 the limit of the zone wherein little or no rain falls should exactly 

 coincide with a change in the constitution of the soil, and I should be 

 more disposed to admit a reversed order of causation, the porous and 

 mobile superficial crust remaining in those tracts wliere, owing to 

 deficient rainfall, there is no formation of vegetable mould, and no 

 accumulation of the finer sediment forming a retentive clay. 



