406 THE POZO STONE. 



The fossiliferous nature of the Pozo Stone, revealed to the 

 naked eye by this gentle weathering, I have further confirmed by 

 an examination of two microscopical slides, kindly prepared by 

 Mr. Thomas Clark, from a chipping of the stone. In composition 

 it is a limestone, with fine bands of pure calcite running through it, 

 and is crowded with fossils, chiefly corals. 



The fifth face of the stone, in area equal to one fourth of the 

 whole surface, is intensely and roughly weathered, yet on it the 

 gradual action of the weathering can be traced from its incipiency 

 to deep hollows. A film-like deposit of oxide of iron, of varying 

 thickness, has had some influence on the intensity and direction of 

 the carving action of the weather, and has preserved portions which 

 run up to sharp edges and prominences. A glance is sufficient to 

 shew that these acute edges and prominences could not have been 

 formed if the stone had been subject to the action of water in the 

 bed of a small stream or river, or to the constant action of spray, 

 their sharpness would have been destroyed and there would have 

 been a rounding off, as on the other parts of the stone. Neither 

 could the hollows have been formed on the weathered surface so 

 deeply if sufficient time had not been allowed for water to chemically 

 eat into or dissolve the stone. 



My belief is that such weathering must have been done by 

 intermittent action, e.g. by the falling of rain at intervals, this 

 meteoric water, ladened with carbonic acid, would dissolve the stone 

 and would remain for some little time. Of course we cannot have 

 rain in a rainless region, but if the stone has registered former 

 Peruvian rainfalls and still carries that record, it is of high value to 

 the physical geologist. In composition it is a limestone, crowded 

 with corals, a deep-sea limestone, and the Andes, like all the highest 

 mountains of the earth, contain limestone formations, their presence 

 in such situations being due to volcanic action ; perhaps nowhere 

 better than in the Chilian and Peruvian regions can we get recent 

 evidence of the intense and enormous lifting of the land, by volcanic 

 disturbances. The Pozo Stone, built by marine organisms and then 

 forming part of an Andian escarpment, is evidence of an elevation 

 of the earth ; such a disturbance of the level of the earth must have 

 caused an alteration in the meteorological phenomena on its surface. 

 A few hundred miles further north occasional showers of rain are 



