Five dredge hauls from the landward flanks(9300--3600 m) of the Philippine Trench at 10¿30'N, northeast of Mindanao, recovered densely plagioclase-clinopyroxene phyric basalt, basaltic andesite, and andesite, with small amounts of diabase. These rocks are all transitional from an arc-tholeiitic to arc-calcalkaline volcanic series and have low Ni and Cr (10--30 and 30--70 ppm, respectively), low TiO2 (0.7--1.2%), and high incompatible element concentrations (Sr, 260--530 ppm; Ba 170--410 ppm). A single dredge on the offshore slope of the trench included aphyric tholeiitic basalt similar to N-type ocean ridge basalts sampled from other locations in the West Philippine Basin (TiO2, 1.0--1.2%; Ni, 70--80 ppm; Cr, 130 ppm; Ba, 2--10 ppm; Sr, 70--85 ppm). The landward samples are distinct from the offshore samples and are identical in texture and composition to arc volcanic rocks from southeast and northeast Mindanao. The Mindanao rocks are interpreted to be part of the Samar-East Mindanao arc, which collided with the Central Mindanao-Sangihe island arc, which collided with the Central Mindanao-Sangihe island arc in the late Oligocene/early Miocene. The volcanic rocks exposed on the landward slope of the Philippine Trench are, apparently, part of the eastern margin of the Samar-East Mindanao arc. After the collision the Philippine Trench was initiated immediately adjacent to the arc massif; there is no evidence of any accretion of material from the subducted Philippine Sea crust. The polarity of the Samar-East Mindanao arc is unknown, but there is no evidence of either a deformed volcanoclastic apron or an older forearc terrane along the trench. Such materials must have been limited in extent prior to collision, have foundered and been subducted as the trench was initiated, or have been faulted or rotated so that they are not locally exposed. ¿ American Geophysical Union 1988