CIIAP, IX, 



Elevation of Coquimbo. 



249 



since been gradually dissolved by water percolating 

 through the mass. 1 



The shells embedded in the calcareous beds forming 

 the surface of this fringe-like plain, at the .height of 

 from 200 to 250 feet above the sea, consist of, 



1. Venus opaca. 



2. Mulinia Byronensis. 



3. Pecten purpuratus. 



4. Mesodesma donaciforme. 



5. Turritella cingulata. 



6. Monoceros costatum. 



7. Concholepas Peruviana. 



8. Trochus (common Valpa- 



raiso species), 



9. Calyptrasa Byronensis. 



Although these species are all recent, and are all 

 found in the neighbouriug sea, yet I was particularly 

 struck with the difference in the proportional numbers 

 of the several species, and of those now cast up on the 

 present beach. I found only one specimen of the Con- 

 cholepas, and the Pecten was very rare, though both 

 these shells are now the commonest kinds, with the 

 exception, perhaps, of the Calyptrcea radians, of which 

 I did not find one in the calcareous beds. I will not 

 pretend to determine how far this difference in the 

 proportional numbers depends on the age of the deposit, 

 and how far on the difference in nature between the 

 present sandy beaches and the calcareous bottom, on 

 which the embedded shells must have lived. 



On the bare surface of the calcareous plain, or in a 

 thin covering of sand, there were lying at a height from 

 200 to 252 feet, many recent shells, which had a much 

 fresher appearance than the embedded ones : fragments 

 of the Concholepas, and of the common Mytilus, still 

 retaining a tinge of its colour, were numerous, and 

 altogether there was manifestly a closer approach in 

 proportional numbers to those now lying on the beach. 

 In a mass of stratified, slightly agglutinated sand, which 

 in some places covers up the lower half of the seaward 



1 I have already had occasion to describe this rock in Chapter VII 



