A borehole, Colston Bassett (South), in Nottinghamshire, England, penetrated Triassic sediments to 1,134 feet, Coal Measures to 2,035 feet, then massive tuffs to 2,714 feet, and finally Millstone Grit to 3,499 feet termination. Another borehole in the vicinity, Colston Bassett (North), shows no tuff, but an equivalent thickness of Coal Measures. Indirect correlation indicates that in Colston Bassett (South) the lower Coal Measures are absent, their place being taken by the tuff, which may represent a cone against which the Coal Measures sediments were deposited. The borehole specimens were chips less than one-eighth inch in size, each sample representing three feet of hole, and presented difficultiesin examination. The tuff consists generally of glass shards, considerably altered to a montmorillonite or closely related mineral, analcime, and a cement of chlorite, calcite, serpentine, ore grains, and fine-grained matter. Dolerite and other igneous fragments are also found with the t