38 PERCY QUENSEL 



Cochcrane brought from the summit (1.500 feet) a piece of black porous lava; 

 and under it he found some dark hardened clay full of cells, the inside of which 

 appear slightly vitrified. The island seems chiefly composed of this porous lava; 

 the strata of which, being crossed at right angles by a very compact black lava, 

 dip on the eastern side of the island about 22° and on the west side 16°, pointing 

 to the centre of the island as an apex" (i, p. 198). 



In 1830 C. Bertero published some observations under the title 'Notice 

 sur I'Histoire naturelle de I'ile Juan Fernandez'. With regard to geological ques- 

 tions he says: "Je pense qu'un geologue n'y trouverait que du basalte dans les 

 etats, meme dans celui de la plus parfaite decomposition; plusieurs blocs sont 

 parsemes d'une cristallisation particuliere, a laquelle on donne, je croix, le nom 

 d'olivine ... II n'y a pas de trace de volcan; les pierres qu'on prend pour 

 de la lave, et dont quelques-unes ressemblent assez aux scories ou de la pierre 

 ponce, ne sont, a mon avis, que du basalte decompose; on trouve aussi cette 

 roche sous forme spherique, et composee de couches concentriques ..." (2, 

 p. 345; compare in the latter respect Fig. 10 on page 52 of this paper). 



A. Caldclelgii, w^ho accompanied Captain P. Parker Kixc; on the sur- 

 veying voyages of H. M. S. Adventure and Beagle on their first expedition 

 1826 — 1830, read before the Geological Society of London on Jan. 5th, 1831, a 

 statement on 'The geology of the island of Juan Fernandez'. In the Proceedings 

 of that year the following account of Caldcleugh's discourse is given: ''The 

 author could discover no trace of a volcano, said to exist here by former visitors; 

 all the rocks, according to him, consist of basaltic greenstone and trap of various 

 mineralogical structure, both amorphous and vesicular, together witli trappean 

 concretions, no other contained minerals being observable except oli\ine and 

 chaux carbonatee metastatique. It is further mentioned that the basalt in parts 

 is almost columnar, and in others has a peaked and serrated outline, the mass 

 being, here and there, traversed by dykes. Owing to the peculiar character of 

 this basalt, and especially from the great quantity of olivine, the author compares 

 its age with that of the basalt of Bohemia, the Rhine, the Vivarrais and Beaulieu 

 in Provence" (3, p. 256, also published in the Phil. Mag. and Annals of Philosophy, 

 Vol. IX, 1 83 1, p. 220). 



Captain King recapitulates Caldcleugh's narrative, as given above, with the 

 addition: "In captain Hale's interesting journal, there is a list of geological and 

 mineralogical specimens, of which one from Alasafuera is named vesicular lava" 

 (4, p. 304). The ultimate destiny of these specimens is unknown. 



Members of the Dumont d'Urville expedition, when visiting Masatierra in 

 1838, collected and specified several different samples of the lavas from the island 

 (5, p. 114). The material for the new analyses of basalts from Masatierra, which 

 Lacroix recently caused to be made and which will be referred to later on, are 

 evidently from this collection, as Lacroix says they were made from s{)ccimens 

 collected by the Dumont d'Urville expedition. G. GRANGE records some observa- 

 tions as follows: "Toutes les roches appartiennent a diverses varietes de trajip 

 et de diorite basaltique amorphes et vesiculaires, on ne trouve dans ces rociies 

 volcaniques aucun autres mineraux que de I'olivine et de la chaux metastatique. 



