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The Blachke Island complex described in detail and two other complexes treated briefly are 3 of at least 8 well-defined ultrabasio intrusive masses in southeastern Alaska, each of which contains all or parts of a genetically related sequence of basic to ultrabasic rocks including dunite, pyroxenite, hornblendite, and gabbro with gradational facies and minor variants. These complexes are emplaced in a variety of terrains, including both Paleozoic and Mesozoic rocks, all of 7/hich have undergone deformation and igneous intrusion during a late Jurassic or early Cretaceous orogeny culminating in the emplacement of the Coast Range batholith., The ultrabasio intrusion arc correlated "with the earliest phases of intrusive activity and antedate-cl-.. ...ore :.iclo and alkalic intrusions. The Blashke Island comple:; .;. :ts " a ..j.^'l.' circular core of dunite 6,000 feet to 9,000 feet in diameter encircled ,;,-a ring .-' olivine aug-itite from a few hundred to 1,500 feet vrido, outside ..-wliJLcli is a nearly complete ring of gabbro, locally absent and ranging up to I 5'.^0 fc^-j '.vide. Host of the dunite core contains only chromits and olivine as primary phases. Near the margin augita is present ac a late primary phase and tho rock passes into augite dunite or wehrlite. The olivine augitite ring contains essentially only augite and olivine, but near its outer margin a little anorthite and hornblende are present sporadically as late primary phases. Tho gabbro is irregular in composition and texture, but toads to pc^ss from an olivine-augite gabbro near its inner contact with olivine augitite into £. hornblende gabbro near the outer margins where it is wideo Well-defined dikes up to a foot wide of augite dunite and wehrlite cut both the dunite and the olivine augitite and thin dikes of augitite out narginal parts of the dunite core. * j.

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