Dr Tschudi on Guano 299^ 



the islands, and on most of the uninhabited promontories of 

 the West of South America, especially in those parts within 

 the tropics. I have often been assured that beds of Guano, 

 several feet high, covered with earth, are found inland at some 

 distance from the sea; but I never met with any, and I have 

 some doubts of the correctness of the statement. If, however, 

 these inland strata really exist, I am inclined to believe that 

 they can only be found on hilly ground ; and in that case they 

 afford strong evidence of a considerable elevation of the coast. 



Guano is formed of the excrements of different kinds of 

 marine birds, as mews, divers, sheerbeaks, &c. ; but the species 

 which I can name with more precision are the following : — 

 Larus modestus, Tsch. ; Rhinchops nigra, Lin.; Plotus An- 

 hinga, Lin. ; Pelecnnus thayus, Mol. ; Phalacrocorax Gai- 

 mardiiy and aWigula, Tsch. (Felecanus Gatmardii, Less; 

 Carbo albiguhi^ Brandt) ; and chiefly the Sula variegtita, 

 Tsch. 



The immense flocks of these birds, as they fly along the 

 coast, appear like clouds. When their vast numbers, their 

 extraordinary voracity, and the facility with which they pro- 

 cure their food, are considered, we cannot be surprised at the 

 magnitude of the beds of Guano, which have resulted from 

 uninterrupted accumulations during many thousand years. I 

 kept for some days a living Sula variegala, which I fed abun- 

 dantly with fish. The average weight of the excrement daily 

 was from three-and-a-half to five ounces. I have no doubt 

 that when the bird is in a state of freedom, the weight must 

 be much greater ; for these birds are constantly plunging into 

 the sea, in order to devour the fishes, which they find in ex- 

 traordinary masses around all the islands. When an island is 

 inhabited by millions of sea-birds, though two-thirds of the 

 Guano should be lost while flying, still a very considerable 

 stratum would be accumulated in the course of a year. 



The marine birds nestle on the uninhabited islands*, or on 

 rocks near the shore; but they never settle on the flat beach, 

 or any place distant from it inland. On this fact I ground 

 my conjecture, that those beds of Guano in the interior, which 

 may have been removed from the shore by important eleva* 

 tions of the coast, are to be found only on hills. 



