39° Tertiary Formations. pake n. 



pitchstone, with, the interstices charged with powdery 

 carbonate of lime apparently of contemporaneous origin. 

 These lavas are conformably associated with strata of 

 breccia and of brown tuff containing lignite. The 

 whole mass has been broken up and tilted at an angle 

 of 4:5 : . by a series of great volcanic dikes, one of which 

 was thirty yards in breadth. This volcanic formation 

 resembles one. presently to be described, in Chiloe. 



Huafo. — This island lies between the Chonos and 

 Chiloe groups : it is about 800 feet high, and perhaps 

 has a nucleus of metamorphic rocks. The strata which 

 I examined consisted of fine-grained muddy sandstones, 

 with fragments of lignite and concretions of calcareous 

 sandstone. I collected the following 1 extinct shells, of 

 which the Turrit ell a was in great numbers : — 



1. Bulla cosmophila. G-. B. Sowerby, PL III. f. 35. 



2. Pleurotorna subaequalis. do. PI. IV. f. 52. 



3. Fusus cleryanus, d'Orbig. « Voy. Pal.' PL XII. f. 6, 7 (also at 



Coquimbo). 



4. Triton leucostomoides, G. B. Sowerby, PL IV. f . 61. 



5. Turriteila Chilensis, do. PL IV. f. 51 (also Mocha). 



6. Venus, probablv a distinct species, but very imperfect. 



7. Cytheraea (?) sulculosa (?), do. PL II. f. 14." 



8. Dentalium majus, G-. B. Sowerby, PL II. f. 3. 



Chiloe. — This fine island is about 100 miles in 

 length. The entire southern part, and the whole 

 western coast, consists of mica-schist, which likewise is 

 seen in the ravines of the interior. The central moun- 

 tains rise to a height of 3,000 feet, and are said to be 

 partly formed of granite and greenstone : there are 

 two small volcanic districts. The eastern coast, and 

 large parts of the northern extremity of the island are 

 composed of gravel, the boulder formation, and under- 

 lying horizontal strata. The latter are well displayed 

 for twenty miles north and south of Castro ; they vary 

 in character from common sandstone to fine-grained, 

 laminated mudstones : all the specimens which I ex- 



