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Hydrothermal convection initiated by emplacement of the gabbro-syenite complex of Abu Khruq into the Egyptian basement 89 Ma ago systematically altered the trace element and isotopic compositions of the syenites. The scale of Sr transport in migrating solutions was far larger than the scale of Sr isotopic equilibration within rocks. As a result, Sr exchange was heterogeneous in the syenites, an effect which can be observed on three different scales. Within grains of a single mineral species, heterogeneities are related to grain boundaries and microfractures through which fluids migrated. Among minerals within rock samples, heterogeneities are related to differences in susceptibility to Sr alteration. Among samples within a single unit, heterogeneous alteration is apparently related to differences in permeability close to fracture zones. During the early stages of alteration radiogenic Sr derived from the country rocks was added to the syenites, causing small net changes in concentration (5 ppm ave.). Some Rb-Sr mineral isochrons from single rock samples yield the emplacement age because isotopic equilibration of this added Sr sometimes occurred within rock specimens. However, regressions of the whole-rock Rb-Sr data yield apparent ages that are about 10 Ma too old. Later stage alteration involved larger changes in whole-rock Sr concentration (45 ppm ave.) but had little further effect on the isotopic relationships because the Sr was derived from cogenetic gabbros rather than the country rocks. Alterations of Rb, Sr, and Sr isotopic compositions are not well correlated with changes in 18O/16O ratio because mineralogy played an important role in decoupling trace element and oxygen isotopic alteration. In general, the absence of such correlations for whole-rock data is not diagnostic of rocks with unaltered trace element and isotopic compositions. Mineral-scale Sr isotopic heterogeneities associated with grain boundaries and microfractures may be the most unambiguous evidence of trace element mobility.

Rb-Sr and K-Ar age detenninations on biotite and muscovite from crystalline rocks in the Vosges and in the Massif Central in France and in the Schwarzwald in Germany are concordant and fall between about 280 and 330 million years. Measurements on zircons give discordant and ambiguous results. Some of the zircons contain large amounts of common lead, much of it in leachable form. Stratigraphically the rocks fall into two time groups, the older late Visean and the younger late Westphalian or early Stephanien. Recent revisions in the stratigraphy of the Vosges and the Massif Central require a corresponding increase in the time-scale value assigned to the boundary between Early and Late Carboniferous (to about 330 million years).

Stratigraphic field studies and nuclear age determinations outline a vast belt of essentially contemporary crystalline rocks extending from southern England through France eastward into central Europe and Asia. The belt (here referred to as the Hercynian complex) lies south of the Scandinavian-Baltic-Ukrainian shield area and north of the Alpine-Himalayan chain. The stratigraphic ages of the crystalline rocks in this belt fall into late Visean to Stephanian (Carboniferous) time wherever they can be determined. Nuclear ages measured on rocks of this belt by several methods on mica, zircon and uraninite fall within the bracket of about 290 to 330 million years ago. It is concluded that a large expanse of rock in Europe and Asia intruded (or was heated and metamorphosed enough to remove radiogenic daughter isotopes) and then cooled within a geologically short period in Carboniferous time. Isolated intrusive and volcanic events took place in Permian time but most of the belt remained unaffected until the large-scale Alpine events of about 20 million years ago.

The intensity distribution of secondary gamma radiation resulting from neutron capture has been measured in simulated drill holes, of various types such as cased and uncased, empty and water‐filled. The intensity of neutron‐capture gamma rays depends on the hydrogen content of the rock. In a six‐inch well, it increases with hydrogen content at points within about 16 inches of the neutron source and decreases at more distant points. The absolute gamma intensity is greatly reduced when non‐hydrogenous gamma‐ray or neutron absorbers, e.g., lead or boron are introduced between logging probe and formation. The slope of logarithmic gamma ray intensity vs. distance remains virtually constant. It changes with the hydrogen content of the formation and offers a means of quantitatively estimating porosity behind casing despite extraneous absorption. The slope can be measured automatically in the well by two gamma detectors placed in a probe at fixed distances from a neutron source. Hydrogenous material between probe and rock increases the slope. Two or three inches of drilling mud seriously impair the sensitivity. Gamma radiation scattered by the walls of drill holes necessitates proper shielding for detectors used in (n, γ) logging with a radium‐beryllium source. A shielded detector is predominantly sensitive to the hard neutron‐capture gamma rays and tends to discriminate against the softer scattered radiation. The scattered intensity decreases with increasing bulk density of the formation. Under favorable conditions, continuous logs of formation density as a function of depth can be obtained.

Experiments were performed to determine the distribution of thermal neutrons and of indium resonance neutrons in continuous hydrogenous media and in pipes passing through hydrogenous media. Included in the study were water, brine, mixtures of sand and water, and mixtures of sand and brine. Experiments in a continuous typical barite drilling mud showed that the neutron distributions were essentially the same as in water. Also, from the point of view of these experiments, oil and fresh water are nearly identical. These experiments show that well fluid (and, by inference, cement) imposes serious limitations on the sensitivity and accuracy of the neutron‐neutron logging method. The indium resonance neutron response (or, in general, the intensity of epithermal neutrons) is a more reliable indicator of hydrogen content of the formation than is the thermal neutron response. The neutron‐neutron method of chlorine determination was found to be not sensitive enough to be useful with brines of the concentrations ordinarily found in reservoirs.

K/Ar and Rb/Sr age determinations on granitic rocks of the Karkonosze and Kudowa plutons in south-western Poland give values around 320 m.y. and thus indicate that these bodies are part of the Hercynian complex of central and western Europe. A core sample from the buried crystalline basement near Eelk (Lyck) in northern Poland also gives a Hercynian age of 320 m.y., but two other basement cores from north-eastern Poland give ages around 1400 m.y. The western boundary of the buried Ukrainian shield presumably lies in north-eastern Poland.

A series of K-Ar, Rb-Sr, and Pb/alpha age measurements in Maine, New Hampshire, and Vermont indicates a complex history of intrusion and metamorphism. Evidence of Grenville age (about 1000 million years ago) is preserved in southwestern Vermont, and subsequent major events in Devonian (400 to 350 million years ago), Permian (270 to 230 million years ago), and Jurassic time (180 to 130? million years ago) are observed. The Appalachian age pattern is similar to that reported from the Ural Mountains and may indicate a tectonic time relationship between the Appalachians and the Urals.

___________________________________ 213 Introduction.-----.--.-______________________________ 213 Acknowledgments _____________________________________________ 214 Hand-portable scintillation counter__________________________________ 215 Physical design____________________________________________ 215 Electronic design..._______________________________________ 216 Calibration.________________________________ 220 Spectrometry_ __________________________________ 221 Special applications.________________________________________ 221 Airborne-carborne scintillation counter ______ _ _ ____ _ ____ _ _________ 222 Physical design____ ____________________________ 222 Electronic design_______________________________________ 223 Response..______.__________________________ 227 Portable scintillation gamma-ray well-logging instrument--_ ___ ____ 232 Physical design________________________________________ 232 Electronic design..____...___________________________ 234 Calibration. _________._________________________ 237 Selected bibliography...____________________________._ 240

THE ‘hard rock’ below the pre-Cambrian unconformity has been searched for fossils the world over, but the results are still few and frequently indistinct. Fossils, ranging from real to very dubious, have been described from the pre-Cambrian of Canada, Finland, India and the United States. The present note announces a new find from Michigan. A more complete report is under preparation.