244 Elevation of Valparaiso pabt n. 



during a gradual elevation of the land. The presence, 

 however, of so many whole and perfectly preserved 

 shells appears at first a difficulty on this view, consider- 

 ing that the coast is exposed to the full force of an 

 open ocean : but we may suppose, either that these 

 shells were thrown during gales on flat ledges of rock 

 just above the level of high-water mark, and that 

 during the elevation of the land they were never again 

 touched by the waves, or, that during earthquakes, such 

 as those of 1822, 1835, and 1837, rocky reefs covered 

 with marine-animals were at one blow uplifted above 

 the future reach of the sea. This latter explanation is, 

 perhaps, the most probable one with respect to the beds 

 at Concepcion entirely composed of the Mytilus Chi- 

 loensis. a species which lives below the lowest tides; 

 and likewise with respect to the great beds, occurring 

 both north and south of Valparaiso, of the Alesodesma, 

 donacif'jnne, — a shell which, as I am informed by Mr. 

 Cuming, inhabits sand-banks at the level of the lowest 

 tides. But even in the case of shells having 1 the habits 

 of this Mytilus and Mesodesma, beds of them, wherever 

 the sea gently throws up sand or mud, and thus protects 

 its own accumulations, might be upraised by the slowest 

 movement, and vet remain undisturbed bv the waves of 

 each new beach-line. 



It is worthy of remark, that nowhere near Valparaiso 

 above the height of twenty feet, or rarely of fifty feet, 

 I saw any lines of erosion on the solid rocks, or any 

 beds of pebbles ; this, I believe, may be accounted for 

 by the disintegrating tendency of most of the rocks in 

 this neighbourhood. Nor is the land here modelled 

 into terraces : Mr. Alison, however, informs me, that 

 on both sides of one narrow ravine, at the height of 

 300 feet above the sea, he found a succession of rather 

 indistinct step-formed beaches, composed of broken 



