236 BULLETIN OF THE 
Of the numbers given below, the first is that of the specimens as 
now entered upon the Museum Catalogue, and the second, enclosed in 
parentheses, is that by which the specimen is known in the records of 
the Fish Commission. 
67526 (8110). Basalt. Wreck Bay, Chatham Island: near haci- 
enda of Mr. Cobos. This is an ordinary basalt, consisting of a dark 
gray vesicular mass, which in thin sections is seen to be made up of faint 
wine-colored augites in very irregular forms, lath-shaped plagioclases, 
small opaque particles of iron ore, and numerous large, clear, faintly 
greenish blebs of olivine. No. 67527 (8111), from the same locality, 
offers no difference worthy of note. 
67528 (8113). Basalt. Landing on northwest face of Malpelo Island. 
This rock much resembles the las* in mineral composition and structure, 
with the exception that extensi e alteration has badly obscured the 
groundmass, and given rise to abundant chlorite, epidote, calcite, and 
sundry ferruginous decomposition products. The presence or absence 
of a glassy base cannot with certainty be determined. In the hand 
specimen this is a finer grained, more dense rock than 67526 or 67527, 
and shows small amygdaloidal cavities filled with a white zeolite. The 
general aspect is that of an older rock than the others (perhaps a mela- 
phyr) though obviously it will not do to speak too positively from an 
examination of the section alone. 
67531 (8116). Andesite (!). Near Chatham Bay, on Cocos Island. 
In the hand specimen this is a light brownish gray, fine-grained, in 
some cases vesicular rock, studded with small (1-2 mm.) white specks 
indicative of feldspar, but in which none of the constituents are of such 
size as to be accurately determined by the eye alone, or even when 
aided by the pocket lens. The thin section under the microscope 
shows a dense aggregate of stout feldspars which are in part sanidins 
and in part a soda-lime variety, obscurely striated, and occurring in 
stout lath-shaped forms. The structure is indistinctly granular, and 
occasionally slightly porphyritic through the development of the larger 
feldspar above noted. So far as observed there is no interstitial glass. 
Abundant red ferruginous and opaque hornblendes, granules of iron ore, 
minute colorless apatites, and ferruginous decomposition products com- 
plete the list of determinable constituents. 
