I'KRiV (JlKNSKL 



li()uc\cr, \cr\- nuich altered to serpentine, chlorite and prehnite. Secondary albite 

 and some scapolite is also j)resent toj^ether with abnndant pyrite. Small cavities 

 are tilled with epidote ami calcite. in the slaj^i^y lavas in the immediate vicinity 

 lai\L;er ca\ ities are tilled with a j)iirel\- white cla>--like substance which was found 

 to be newtonite. In intimate association with this mineral is nearly always found 

 a vellowi^ii waw substance which shows ever\' resemblance to what mineralogi- 

 call\- ma\- be si^nitied as bole (I''i<;. 13). It is very brittle with a conchoidal 

 fraclme. in water it readil\' disintegrates into small angular fragments. Tliis bole 

 mineral is also t'ound tilling cracks, or occurs in smaller masses in the cavities 

 of the basalts around the baw 



in t!ie agglomeritic lavas of the vicinit)- large cavities are filled with hard 

 compact magnesite. As earl\- as 1886 Darapsky described this mineral by the 

 r.ame "( ilockenstein" and gave an analysis thereof, which shows it to be an 

 exceptionall)- pure magnesite (9, p. I 13). Without doubt the magnesite is primarily 

 derued tVom olivine, the decomposition being caused by the same processes as 

 ha\e changed the basaltic lavas nearby. 



The whole asj^ect of the rocks from l^ahia del Padre, with magnesite, calcite, 

 serpentine, chlorite, sca{)olite and pyrite as secondary minerals, seems without 

 doubt to indicate that the lava beds in question have been subjected to alterations 

 in connection with thermal processes during some intermediate phase of volcanic 

 activity on the island. There seems no reason to classify them as andesites of 

 an older formation, as is done by Schulze and Pohlmann. 



In a s[)ecimen collected by Skottsberg from the shore south of El Yunque, 

 Ilagerman also tound evidence of a far-reaching decomposition. Under the heading 

 "! Ixclrothermale I^ildungen" he gives the following description: "Das Handstiick 

 ist ein von weissen .Streifen durchzogenes scharfgriines Gestein, das u. d. M. 

 grosse Augitkristalle in einer vollig zeri^ossenen Serpentinmasse zeigt. Das Pra- 

 ))arat ist von Aragonitbandern durchzogen. Dieses Gestein muss als ein stark 

 umgebildetes ( )livinfels bezeichnct werdcn" (13, p. 27). The large olivine crystals of 

 the duniti'. tound as inclusions in the picrite basalt at Puerto Prances, show, on the 

 contrarx-, no signs of secondar\- alteration (see p. 47). There is therefore no doubt 

 that the higiily decomposed '( )hvinfels' described by Hagerman has succumbed 

 to a later decomposition of much the same nature as has been active around 

 I)ahia (K-1 I'adre. 



Masafuera. 



I. at. ^y 52' S.. Lon^. <So'' 54' W. : 



1 he la\as ot Masafuera piesent a more varying aspect than those of Masa- 

 tierra and contam .sc\cral t>pes of petrographic interest. They have, however, 

 hitherto only been sinumanl\- described in the j)a|)ers by myself (l 2, p. 274) and 

 b\' I lagerman 1 1 3. p. j8i. 



I he rocks which predominate at lower levels are mostly vesicular to slaggy 

 basalts. The\- are well represented around the Ouebrada de las Casas. At higher 

 levels the basalts consist of more compact lava beds. In contrast to the basalts 



