2©4 SMITHSONIAN MISCELLANEOUS COLLECTIONS [vOL. 45 



Alianaitsunguak, however, lying to the west of Ata, olivine basalt 

 was collected in a fairly good state of preservation. At Atanekerd- 

 luk, on the southeastern coast, some specimens were collected, 

 among them olivine gabbros and monzonite, the former constituting 

 the main mass of the small peninsula. The only representation of 

 this large areal extent is a single hand specimen (Cat. No. 75,490), 

 somewhat decomposed, but still well enough preserved to admit of 

 satisfactory examination. In color it is old rose, spotted here and 

 there with what appears to be a secondary mineral, but which on 

 examination in thin section proves to be a surprisingly fresh 

 pyroxene. Sometimes this green, mineral forms a continuous net- 

 work in the red feldspar. It is this latter constituent which forms 

 the bulk of the rock and from which nearly all the secondary con- 

 stituents have been derived. Among these latter, calcite is readily 

 distinguished, occurring in tiny anhedrons throughout the red 

 plagioclase ground mass. 



Viewed in thin section the rock presents a hypautomorphic 

 granular appearance. Among the most abundant minerals is 

 pyroxene. It is light brownish in hue, approaching at times a violet. 

 Prismatic sections, both 100 and 010, were observed, the latter giving 

 extinctions as high as 52.9°. These sections are naturally most 

 numerous, but octagonal basal sections showing both prismatic 

 cleavages were surprisingly well developed. Twins of the usual 

 variety, the twinning plane being the orthopinacoid (100) were 

 noted. With the lowest powers of the instrument the augite appears 

 perfectly fresh. Even the highest powers prove that decomposition 

 has not advanced very far. Even those parts of this mineral which 

 project into thoroughly decomposed parts of the rock, consisting 

 mainly of viridite, are plainly discernible, their crystalline outlines 

 showing with much distinctness. Naturally in such areas the augite 

 is much decomposed, but the evidence is plain that the greenish 

 residual product is not chiefly derived from the augite. Along its 

 cleavage planes foreign matter has filtered in, while a portion of 

 such material has been produced in situ. Inclusions of hydrous 

 iron ore and magnetite are present. Thus, to summarize, we may 

 say that, although the augite has slightly altered, alteration has 

 taken place only at vulnerable points and it is yet the most perfectly 

 preserved of the constituents. In age it is older than the feldspar. 



Though augite presents the same appearance throughout its entire 

 extent, so far as progress in alteration is concerned, the same is not 

 true of the plagioclase. Though perfectly fresh in spots, it presents 

 all phases of alteration to the fully kaolinized material. It exhibits a 



