Muir Seamount Group.--In 1945 workers on the U.S.S. MUIR discovered a large seamount 140 miles northeast of the Bermuda Islands. Subsequent reconnaissance surveys by the Lamont Geological Observatory (Tolstoy, 1951; Tolstoy and Ewing, 1949) revealed that the peak was asymmetrical in east-west profile (considerably steeper on the east) and that the seamount was elongate northeast-southwest parallel to the axis of the Bermuda Rise. Cores taken near its summit contained Eocene to Pleistocene sediment. Additional seamounts have been discovered in the area by Worzel and Shurbet (1955) and Northrop and Frosch (1954). The asymmetrical profile and the elongate shape parallel to the axis of the Bermuda Rise suggest that Muir Seamount is a tectonic uplift rather than a volcanic pile, but admittedly undersea vulcanism need not always produce symmetrical cones. As known, Muir Seamount is 35 miles wide (northwest-southeast), 60 miles long (northeast-southwest), and rises 1700 fathoms above the Bermuda Rise. The minimum sounding recorded is 846 fathoms. The Muir Seamount and near-by associated peaks apparently are not directly related to the Kelvin Seamount Group farther north. The north and northwest margin of the Bermuda Rise, like that on the west, is in some places a scarp and in other places a gentle transition. Near the northwest corner of the Bermuda Rise a range of hills each about 20 fathoms high and 3 miles wide follows the margin of the rise for many miles. The northeastern margin of the Bermuda Rise is abrupt in most places, and in some places a single scarp 500 fathoms high is all that separates the Bermuda Rise from the adjacent abyssal plain. Sediments of the Bermuda Rise.--Most of the Bermuda Rise lies below the depth of 2500 fathoms, and thus the sediment ranges from foraminiferal clay through red clay with a predominance of red clay. In the vicinity of the Bermuda Pedestal calcareous detrital sediments have built a depositional apron around the base of the pedestal in depths of 2300 to 2450 fathoms (Pl. 28). The seamounts of the Bermuda Rise are rocky, as shown by photographs and bottom samples. Several cores from the Muir Seamount revealed a variety of Tertiary foraminiferal lutites. With the exception of the detrital sediments of the Bermuda Apron, the scoured crests and flanks of the larger seamounts, and the steeper scarps, the Bermuda Rise is covered preponderantly by pelagic sediments. This is in sharp contrast to the surrounding abyssal plain and near-by continental rise, where cores reveal frequent alterations of detrital and pelagic sediments (Pl. 28).