404 Tertiary Formations. part ii. 



reous matter, and I did not donbt that it belonged to 

 the same recent formation with the gravel on the sur- 

 rounding plains, also cemented by calcareous matter, 

 until to my surprise, I found in the midst of it, a single 

 thin layer almost entirely composed of the above gigantic 

 oyster. 



At a little distance inland, I obtained several sections 

 of the bed (E), which, though different in appearance 

 from the lower bed (F), belongs to the same formation : 

 it consists of a highly ferruginous sandy mass, almost 

 composed, like the lowest bed at Port S. Julian, of 

 fragments of Balanidas ; it includes some pebbles, and 

 layers of yellowish-brown mudstone. The embedded 

 shells consist of: — 



1. Monoceros Blainvillii, d'Orbis:. 'Yovage Pal.' 



2. ambiguus, G. B. Sowerby,~Pl. IV. f. 66, 67. 



3. Anoniia alternates, do., PL II. f. 25. 



4. Pecten rudis, do., PI. III. f . 32. 



0. Perna Gaudichaudi, d'Orbig. ' Voyage Pal.' 



6. Ostrea Patagonica (.') do. 



7. Ostrea, small species, in imperfect state ; it appeared to me 



like a small kind now living in, but very rare in the bay. 



8. Mytilns Chiloensis ; Mr. Sowerby can find no distinguishing 



character between this fossil, as far as its not very perfect 

 condition allows of comparison, and the recent species. 



9. Balanus Coquimbensis, G. B. Sowerhy, PI. II. f. 7. 



10. Balanus psittacus? King. This appears to Mr. Sowerby and 

 myself identical with a very large and common species now 

 living on the coast. 



The uppermost layers of this ferrugino- sandy mass 

 are conformably covered by, and impregnated to the 

 depth of several inches with, the calcareous matter of 

 the bed (D) called losa : hence I at one time imagined 

 that there was a gradual passage between them ; but as 

 all the species are recent in the bed (D), whilst the 

 most characteristic shells of the uppermost layers of (E) 

 are the extinct Perna, Pecten, and Monoceros, I agree 

 with M. d'Orbigny, that this view is erroneous, and that 

 there is onlv a mmeralosncal passage between them, 



