ADDITIONAL COMMKN 1 S (iN IHK (IKOI.OGN OK i HK JUAN KF.KNANDKZ ISLANDS 53 



as representing recent tuffacious material. The one he describes as "ein poroses, 

 dichtes Gestein von FA Puente, dem Istmus zuischen der Padrebiicht und Carbajal 

 iind ist ein Palagonittiiff niit einigen sporadischcn Augit- und Magnetitkcirnern. 

 1 )cr amlcre Tuff staniint noii tleni nordliclicn L'fcr der Padrcbucht, von wo einige 

 unigewandcltc ()li\inbasalte herriihren" 1 13, p. 26). As these specimens have 

 been collected without any observations regarding their petrological position, one 

 cannt^t chaw any conclusive evidence as to their age, but tlie sj)ccimens from both 

 the locahties have e\ery appearance of being recent pyroclastic sediments. 



I have previously described rocks from I^ahia Cumberland, filling out the 

 greater j)art of the ba\', which 1 assumed to be of recent tufifaceous origin. The 

 description was gi\cn as follows: "In den zentralen Teilen von Cumberland l^ay 

 liegen noch ziemlich miichtige, meist lebhaft rot gefarbte Tufflager, die sehr stark 

 umgewandelt sind. Bruchstiicke von Olixinkristallen, la[)illiartige Lavabruchstucke, 

 ICrzkdrner uiul (das liegen in einer (irundmasse, die aus einer weichen, mit Messer 

 schneidbaren, roten lateritahnlichen Lehmsubstanz besteht, die durch Verwitterung 

 aus dem urspninglichen Tuffmaterial hervorgegangen sein diirfte. Uberall in den 

 Tuffsedimenten ist eine deutliche Lagerung sichtbar" (12, p. 266). It is over 40 

 vears since I visited the locality and naturall\- I cannr)t ncnv rely on any personal 

 recollection. The inundation in connection with the volcanic disturbance of ICS35, 

 referred to above (p. 41), may have wrought such havoc, that superficial deposits 

 could ha\e been re-formed. Hut the composition of the formation, as well as my 

 notes from the field, offer indications that the tuffaceous material of Bahia Cumber- 

 land also represents pyroclastic sediments of recent volcanic origin. 



Even if onl\- trivial remains of tuffaceous formations, indicative of late volcanic 

 activit}' on the island, are left, the submarine explosion of 1 835 confirms without 

 doubt that the area in the immediate \icinity has at that time been subjected 

 to disturbances of volcanic nature. 



Some rocks from around Bahia del Padre deserve special notice. Schulze 

 and Pohlmann have observed the deviating nature of the rock assemblage and 

 the latter has commented thereon as follows: "De suma importancia para esplicar 

 la formacion jeolojica de Masatierra es la entrada a Bahia del Padre, situada en 

 la parte suroeste de la isla. Aqui se observa debajo de las capas basalticas ya 

 descritas un grand macizo de roca compacta \erdosa, que es andesitica. Segun 

 la opinion de Schulze' que, a me parecer, es correcta, esta roca verdosa es la 

 mas antigua de la isla. V.n ningun otro punto, ni en ^Masatierra, ni en Masafuera 

 se ha observado una configuracion jeolojica analoga a la mencionada" (ii, p. 4). 



The rocks referred to by Pohlmann certainly show a divergent aspect. But 

 I do not think they can be taken as representing rocks belonging to a more 

 ancient formation than the lavas around, nor that they should be classified as 

 andesites, as Pohlmann has assumed. I have as the result of microscopical 

 examination of the rocks come to the conclusion that the deviating character is 

 the result of post-volcanic alterations through thermal processes. In my earlier 

 paper I have given in some detail the reasons for this conclusion (12, p. 266), and 



' Dr. Schulze died before publishing his observations. 



4 — 516795 The Xat. Hist, of Juan Fernandez and Easter Isl. Vol. I. 



