Shear and longitudinal velocities were measured by the ultrasonic phase comparison method as a function of pressure to 8 kbar on synthetic glasses of basalt, andesite, rhyolite, and quartz composition and on natural obsidian. Velocities of most of the glasses decrease anomalously with pressure, but increasingly more‐normal behavior occurs with decrease in SiO2 content. The pressure derivatives of rigidity and bulk modulus increase linearly, from −3.39 to −0.26 and from −5.91 to +2.09, respectively, with decrease in SiO2 content from 100 to 49%. The change from negative to positive in the pressure derivatives of both moduli and observed at Poisson's ratio of about 0.25 is consistent with the Smyth model for the anomalous elastic behavior of glass. If the temperature in the upper mantle is about 1500°C, tholeiitic basalt would be molten in accordance with the partial melt explanation for the low‐velocity zone; at 1300°C and below, basalt would be in the glassy state, especially if more felsic than tholeiite. At a temperature of 1370°C and at 30 kbar, reasonable values for the upper mantle at 100 km depth, the basalt glass of this study would have a viscosity of about 1013 P. On the basis of the theory of viscoelasticity the glass would support shear wave propagation at frequencies above 0.1 Hz. Under such conditions of PT, 10 to 30% basalt glass in a matrix either of eclogite or olivine would reduce the seismic velocities by 3 to 9% and could also account for the values observed in the low‐velocity zone.

Temperatures were measured to a depth of 312 m in a hole cored in granite at 36ø52.15'N, 77ø54.15'W (elevation 116 m), near Alberta, Virginia. The temperature gradient in the lower half of the hole is uniformly 18øC/km. The cause of a variable gradient in the upper half of the hole is thought to be movement of groundwater within the hole. The average thermal conductivity determined from measurements on 0.64-cm-thick disks is 7.8 mcal/cm sec øC, but the average conductivity computed by summing the thermal resistivities of the constituent minerals is 6.2. The corresponding values of heat flow are 1.4 and 1.1 vcal/cm" sec, respectively. The average heat flow in eastern North America is 1.0, and the previously published high in this region is 1.3 tzcal/cm 2 sec. Introduction. Determinations of terrestrial heat flow on the continents number about 100 [Lee, 1963]. 0nly five measurements have been published for the metamorphic zone of the Appalachian Mountains of eastern North America [references in Dimen• and Werre, 1964]. In view of this paucity of data, any borehole that is free from strong thermal perturbations, and from which rock samples have been retrieved, represents an opportunity to supplement knowledge of an important but poorly known geophysical parameter. Site and drilling details. During 1909 and 1910 a hole was cored to a depth of 480 m in granite at 36ø52.15•N, 77ø54.15'W (elevation 116 m above mean sea level), about 1.8 km west of Alberta, Virginia, on the right-of-way of the Norfolk and Western Railway Company, 60 m east of mile post 99 and 5 m north of the track.

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Thermistors are small rugged beads, disks, or rods of sintered oxides, which can be used to measure temperature with a precision of ±0.01°C with a simple four-dial Wheatstone bridge. Thermistors of number 1 material have a spinel crystal structure, the approximate formula being Ni0.6Mn^4Mn+2O4. Thermistors of this material generally are used in temperature sensing, and those with a nominal resistance of 1,000 ohms at 20°C have a negative temperature coefficient of resistance of about 5 percent per deg C at that temperature. Most thermistors differ in resistance and in change of resistance with temperature and so are not interchangeable.An empirical adaptation of the equation for electrical resistivity of semiconductors fits the resistance-temperature data for thermistors very well:R=A exp where R is resistance, in ohms; Tis temperature, in degrees Celsius; and A, B, and C are constants. For this equation, interpolations between 15°C intervals are good to ±0.01°C. The effect of pressure on thermistor resistance is negative and very small, about 10~7 bar"1 ; at the bottom of a 3,000-meter hole, in a logging cable, a thermistor (nominally 50,000 ohms at 20°C) would have a change of resistance of 0.1 ohm, equivalent to + 0.0002°C, due to the pressure of the water column in the hole.In a separate study of precision of measurement, a platinum thermometer was used to determine the absolute temperature of 23 carefully made ice baths (nominally at 0°C), and the mean was + 0.0004° C, the standard deviation being 0.0014°C. These values constitute, respectively, the systematic and the random errors of both the thermometer measurements and the bath temperatures. Five thermistors in the same baths showed a standard deviation of temperature measurement of 0.003°C; however, the coherent variation of the resistances of all five thermistors from bath to bath shows that relative-temperature measurements with thermistors can inherently be as precise as ± 0.0001° C.In the calibrations of 41 thermistor cables at the ice point (0°C) in a large box, the mean temperature as measured by the platinum thermometer was 0.0018° C, and the standard deviation was 0.0031°C. Thermistors in cables can be accurately calibrated in such baths.