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Bottom photographs and drilled rock cores, obtained from several mountain tops along the crest of the Mid-Atlantic Ridge near 45°N, show a patchy distribution of basic igneous rock outcrops and localized mixed deposits of basaltic boulders, cobbles and pebbles, ahermatypic-coral skeletal fragments, and calcareous mud. Coralline limestones repeatedly have been observed underlying unconsolidated pebble and mud deposits.
Between 900 and 1,200 m water depth on the south slope of Confederation Peak (45°23^primeN, 28°10^primeW), outcrops of fractured igneous rock are surrounded by deposits of angular cobbles and pebbles in a calcareous-mud matrix. Downslope, exposed, igneous rock outcrops are surrounded by pebble deposits with about a 60% calcareous-mud matrix. A basalt conglomerate core drilled near the top of this mountain (914 m) is composed of manganese-coated pebble and cobble-sized basaltic fragments cemented by a calcareous matrix that may have lithified, in part, during subsequent vertical uplift of this deposit to its present elevation. At 1,042 m water depth, porous coralline limestone was encountered by the drill after 143 cm of penetration through unconsolidated sediments. The surfa e of the north side of Bald Mountain (45°13^primeN, 28°56^primeW) between 1,555 and 2,380 m is composed of outcrops of basic igneous rock alternating with angular cobble and gravel deposits, probably of similar composition. An intermittent cover of calcareous mud is evident starting at about 1,900 m water depth. Slightly porous and friable, coralline limestone, covered by 81 and 155 cm of coral skeletal material, basaltic pebbles, and calcareous mud has been drilled at 1,426 and 1,682, respectively. Generally, limestones covered by a relatively thin layer of unconsolidated sediment and those situated at relatively shallow water depths show a greater degree of induration. Five whole-sample radiocarbon dates determined for the upper parts of several limestone cores range approxim tely between 31,000 and 39,000 years, suggesting that deposition and (or) lithification may have been associated with a moderately warm interval following the early Wisconsin glaciation (Emiliani's Stage 3).
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