A 145-km-long seismic refraction line recorded parallel to the eastern coastline of Maine within the Avalon terrane provides information about the crustal velocity structure within the Avalon block and its relation to other Appalachian terranes. A crustal velocity model for the upper 8 km, determined by using two-dimensional ray tracing, accounts for all first arrivals on the traveltime curves for each of the shots recorded and shows that, except for a thin surficial layer of velocity 5.0-5.3 km/s, upper crustal granites and country rocks have velocities in the range 6.0-6.3 km/s and gabbros have a 6.5 km/s velocity. To determine the lower crustal structure, deep reflections were analyzed by applying normal moveout corrections routinely used in reflection data processing. Major reflective boundaries at approximately 3-4, 7, and 10-11 s two-way traveltime are easily distinguished, and are similar to those observed in a near-vertical seismic reflection survey crossing the refraction profile at its southwestern end. The deepest reflections correspond to the crust-mantle boundary at a depth of 34-35 km.