chap. xii. Tertiary Formation, 389 



Pampean deposit, and those strata in eastern Tierra del 

 Fuego of doubtful age, as well as the boulder formation, 

 we have a line of more than twenty-seven degrees of 

 latitude, equal to that from the Straits of Gibraltar to 

 the south of Iceland, continuously composed of tertiary 

 formations. Throughout this great space the land has 

 been upraised, without the strata having been in a 

 single instance, as far as my means of observation went, 

 unequally tilted or dislocated by a fault. 



Tertiary Formations on the West Coast. 



Chonos Archipelago. — The numerous islands of this 

 group, with the exception of Lemus, Ypun, consist 

 of metamorphic schists ; these two islands are formed of 

 softish grey and brown, fusible, often laminated sand- 

 stones, containing a few pebbles, fragments of black 

 lignite, and numerous mammillated concretions of hard 

 calcareous sandstone. Out of these concretions at Ypun 

 (lat. 40° 30' S.), I extracted the four following extinct 

 species of shells : — 



1. Turritella su1 uralis, G . B. Sowerby, PL III. f. 50 (also Navidad). 



2. Sigaretus subglobosTS, do. PL TIL f. 36, 37. (do.) 



3. Cytheraea (?) sulculosa (?), do. PL II. f. 14 (also Chiloe and 



Huafo ?). 



4. Voluta, fragments of. 



In the northern parts of this group there are some 

 cliffs of gravel and of the boulder formation. In the 

 southern part (at P. Andres in Tres Montes), there is 

 a volcanic formation, probably of tertiary origin. The 

 lavas attain a thickness ot from 200 to 300 feet ; they 

 are extremely variable in colour and nature, being 

 compact, or brecciated, or cellular, or amygdaloidal 

 with zeolite, agate and bole, or porphyritic with glassy 

 albitic feldspar. There is also much imperfect rubbly 



