chap. xii. Port S. Jtdian and Santa Cruz. i>77 



stone : here and there, however, at various heights, thin 

 earthy layers, containing the great oyster, Pecten Para- 

 nensis and Turritella ambulacrum, are interstratified ; 

 thus showing that the whole mass belongs to the same 

 epoch. I nowhere found even a fragment of a shell 

 actually in the white deposit, and only a single cast of 

 a Turritella. Out of the eighteen microscopic organisms 

 discovered by Ehrenberg in the specimens from this 

 place, ten are common to the same deposit at Port 

 Desire. I may add that specimens of this white mud- 

 stone, with the same identical characters, were brought 

 me from two points, — one twenty miles north of S. 

 Julian, where a wide gravel-capped plain, 350 feet in 

 height, is thus composed ; and the other forty miles 

 south of S. Julian, where, on the old charts, the cliffs 

 are marked as ' Chalk Hills? 



Santa Cruz. — The gravel-capped cliffs at the mouth 

 of the river are 355 feet in height : the lower part, to 

 a thickness of fifty or sixty feet, consists of a more or 

 less hardened, darkish, muddy, or argillaceous sandstone 

 (like the lowest bed of Port Desire), containing very 

 many shells, some silicified and some converted into 

 yellow calcareous spar. The great oyster is here 

 numerous in layers ; the Trigonocelia and Turritella 

 are also very numerous : it is remarkable that the 

 Pecten Paranensis, so common in all other parts of 

 the coast, is here absent: the shells consist of: — 



1. Ostrea Patagonica, d'Orbig. * Voyage Pal.' (also at St. Fe and 



whole coast of Patagonia). 



2. Pecten centralis, G. B. Sowerby, PI. III. f . 31 (also P. Desire 



and S. Julian). 



3. Venus meridionalis of G-. B. Sowerby, PL II. f. 13. 



4. Crassatella Lyellii, do. PI. II. f. 10. * 



5. Cardium pulchellum, do. PL II. f. 15. 



6. Cardita Patagonica. do. PL II. f. 17. 



7. Mactra rugata, do. PL II. f. 8. 



8. Mactra Darwmii, do. PL II. f. 9. 



9. Cucullaea alta, do. PL II. f. 22, 23 (also P. Desire). 



