(Browne, 1973) that seawater contributions are sig-nificant. The lack of marine sediments in either coreshows that all rocks were deposited above sea level.More than 40% contamination of sample 1 by seawaterwould be required to give an isotopic composition ofsample 7.

Water subject to vapor-loss by evaporation becomesenriched in the heavy isotopes. This effect, however, pro-duces waters with a slope of 4 to 5 on a 6D-6180diagram, owing to kinetic isotope effects (Craig, 1963).Also, Browne (1973) has suggested that there is evi-dence for the deep circulation of hot water (up to250 0C.), from secondary mineral studies. Hot waterwould exchange with the rocks, which probably have81808M0W values of +5 to + 8 per thousand, thereby en-riching the 180 in the water (Craig, 1963). These sam-ples, however, do not show any evidence of evaporation,or of hot water exchange with the rocks, as either ofthese effects would enrich 180 more than D, away fromthe line of slope 8.

Analysis of further samples is required to determinewhether there are isotopically discrete bodies of ice inthe cores, and if these can be used to determine paleo-climate variation during the period of deposition.

I thank Mrs. M. A. Cox and Drs. C. B. Taylor, J . R.Huiston, and B. W. Robinson for assistance with anal-yses and many useful comments.

References

Browne, P. R. L. 1973. Preliminary report: secondary mineralsin cores from DVDP drillholes 1 and 2. Northern IllinoisUniversity. Dry Valley Drilling Project. Bulletin, 2.

Craig, H. 1961a. Isotopic variations in meteoric waters. Science,133: 1702-1703.

Craig, H. 1961b. Standard for reporting concentrations ofdeuterium and oxygen-18 in natural waters. Science, 133:1833-1834.

Craig, H. 1963. The isotopic geochemistry of water and carbonin geothermal areas. In: Nuclear Geology on GeothermalAreas (E. Tongiorgi, ed.).

Dansgaard, W. 1964. Stable isotopes in precipitation. Tellus,16: 436-468.

Johnsen, S. J . , W. Dansgaard, H. B. Clausen, and C. C. Lang-way. 1972. Oxygen isotope profiles through the Antarctic andGreenland ice sheets. Nature, 235: 429-434.

Kyle, P. R., and S. B. Treves. 1973. Geological history of HutPoint Peninsula. Northern Illinois University. Dry ValleyDrilling Project. Bulletin, 2.

Lorius, C., L. Merlivat, and R. Hagemann. 1969. Variation inthe mean deuterium content of precipitations in Antarctica.Journal of Geophysical Research, 74: 7027-7031.

Taylor, C. B. 1973. Measurement of oxygen-18 in environmentalwaters using Epstein-Mayeda technique. Part I. DSIR (NewZealand) Institute of Nuclear Sciences Report INS-LN-37.

Taylor, C. B., and J . R. Hulston. 1972. Measurement of oxygen-18 in environmental waters using Epstein-Mayeda technique.Part II DSIR (New Zealand). Institute of Nuclear Sciences.Report, INS-LN-36.

Treves, S. B., and P. R. Kyle. 1973. Geology of DVDP haltno. 1 and 2. Northern Illinois University. Dry Valley Drill.ing Project. Bulletin, 2: 11-83.

Geochemistry of McMurdo volcanicsJOHN S. STUCKLESS

Department of GeologyNorthern Illinois University

During the austral summer field season (1972-1973)samples of the McMurdo volcanics were collected tosupplement the core samples recovered during first drill-ing in the Dry Valley Drilling Project. Collecting wasdone in cooperation with S. B. Treves of the Universityof Nebraska. Localities visited included Cape Crozier,Inclusion Hill, Cape Bird, Cape Royds, Cape Evans,Half Moon Crater, Twin Craters, Bomb Crater, andMount Erebus on Ross Island and Brandau Vent in theRoyal Society Range. At each locality an attempt wasmade to collect representative fresh samples of the vol-canic rock as well as the inclusions and megacrysts thatmight be related to the volcanics. The latter types of ma-terial were collected from surface outcrops because of thelow probability of recovering them in the drill core.

The most striking feature of the inclusions and mega-crysts is the wide variety of rock types, even in one lo-cality. Common inclusion types are dunite, peridotite,pyroxenite, gabbro, and sandstone, all occurring in sizesup to 10 centimeters in diameter. The megacrysts in-clude olivine, spinel, clinopyroxene, hornblende, andanorthoclase, the last three occurring in lengths up to6 centimeters.

A trip to the summit of Mount Erebus showed thatthe volcano is still active, with lava occupying the cen-tral crater. During our 5-hour period of observation,one large explosion threw material approximately 400feet above the crater floor.

This work was supported by National Science Founda-tion grant GV-36951.

Aeromagnetic data from theMcMurdo Sound region

H. K. WONG

Department of GeologyNorthern Illinois University

An aeromagnetic survey of the area covered by theU.S. Geological Survey maps Ross Island and TaylorGlacier was begun in the 1971-1972 field season, whenabout half the flight tracks were flown. The rest wasdone in January 1973. This survey was supported by

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