746 



H. S. WASHINGTON 



abundant colorless glass. Nothing was found which could be con- 

 sidered to be feldspar. There are some small needles of apatite. 

 Nodules. — -The lava flow north of Scano is remarkable for the 

 abundance of nodules of olivine and augite, which have been already 

 partially described by Doelter.' Those of olivine seem to be most 

 numerous. They are rounded, varying in size from that of a hazel- 

 nut to that of one's fist. They are composed of grains, from i to 

 2 mm. in diameter, of a transparent olivine, of a light greenish- 

 yellow color, with a few small grains of magnetite. These grains 

 are not very coherent, the nodules crushing down readily beneath 

 the finger. An analysis of this olivine, extremely fresh, carefully 

 purified and dried at iio°, gave me the results in A (Table I), 



TABLE I 



those in B being an analysis by Doelter {op. cit., p. 78). The spe- 

 cific gravity was 3 . 307 at 20°. The amount of nickel is noteworthy, 

 as is also the entire absence of chromium, an element often occur- 

 ring in olivine. There was only an unweighable trace of manganese 

 and absolutely no lime. Leaving out of consideration the very 

 small amounts of alumina and ferric oxide, as impurities, the ratio 

 RO:(Si, Ti)02=i.99; i.oo, which is that of an orthosilicate. 

 That of FeO: MgO = i : 10. 5, so that the olivine is distinctly mag- 

 nesian. The optical properties of this olivine will be studied 

 later. 



Doelter's analysis is clearly defective. The sum is very low and 

 the relation ROiSiOz does not approach that of an orthosilicate. 



' C. Doelter, op. cit., p. 78. 



