37 S Tertiary Formations. paet n. 



10. Trisronocelia insolita, do. PL II. f. 20, 21. 



11. Nucula (?) glabra, do. PI. II. f. 18. 



12. Crepidula greo-aria, do. PI III. f . 34. 



13. Toluta alta. do. PL IT. f. 75. 



14. Trochus collaris, do. PL III. f. 14. 45. 



15. Natica solida (?), do. PL III. f. 40, 41. 



16. Struthiolaria ornata, do. PL IT. f. 62 (also P. Desire). 



17. Turrit ella ambulacrum, do. PL III. f. 49 (also P. S. Julian). 

 Imperfect fragments of the genera Byssoarca, Artemis, and Fusus. 



The upper part of the cliff is generally divided into 

 three great strata, differing slightly in composition, but 

 essentially resembling the pumiceous mudstone of the 

 places farther north ; the deposit, however, here is more 

 arenaceous, of greater specific gravity, and not so white : 

 it is interlaced with numerous thin veins, partially or 

 quite filled with transverse fibres of gypsum ; these fibres 

 were too short to reach across the vein, have their extre- 

 mities curved or bent : in the same veins with the gyp- 

 sum, and likewise in separate veins as well as in little 

 nests, there is much powdery sulphate of magnesia (as 

 ascertained by Mr. Reeks) in an uncompressed form : I 

 believe that this salt has not heretofore been found in 

 veins. Of the three beds, the central one is the most com- 

 pact, and more like ordinary sandstone : it includes nu- 

 merous flattened spherical concretions, often united like 

 a necklace, composed of hard calcareous sandstone, con- 

 taining a few shells : some of these concretions were 

 four feet in diameter, and in a horizontal line nine feet 

 apart, showing that the calcareous matter must have 

 been drawn to the centres of attraction from a distance 

 of four feet and a half on both sides. In the upper and 

 lower finer-grained strata, there were other concretions 

 of a o-rev colour, containing calcareous matter, and so 

 fine-grained and compact as almost to resemble por- 

 celain-rock : I have seen exactly similar concretions in 

 a volcanic tufaceous bed in Chiloe. Although in this 

 upper fine-grained strata, organic remains were very 

 rare, yet I noticed a few of the great oyster; and in 



