Blasts at two quarries in northern New York and central Pennsylvania have been recorded to a distance of 309 km. The data indicate an essentially homogeneous, unlayered crust, with elastic wave velocities possibly increasing with depth. An average crustal thickness for the region is 34.4 km., with no indication of significant difference in thickness between the two areas. Observed compressional wave velocities for the crust are 6.39 and 6.31 km/sec. for New York, and 6.04 km/sec. for Pennsylvania. The corresponding shear wave velocities are 3.62 and 3.60 km/sec., and 3.61 km/sec. Average upper mantle velocities are 8.14 km/sec. for Pn and 4.69 km/sec. for Sn. The compressional wave velocity of anorthosite near Tahawus, N.Y., is 6.63 km/sec. No near-vertical reflections from the Mohorovičić discontinuity were observed.

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