Large pipes of brecciated Torridonian (Precambrian) sediments in a calcite matrix are described from three localities on Raasay off the northwest coast of Scotland. They are morphologically similar to explosion vents but contain no igneous material, and no limestone occurs at depth from which the source material of the calcite matrix could have been leached by hydrothermal solutions. Origin of the vents is attributed to explosive fumarolic activity during Tertiary volcanism, and the carbonate of the matrix is considered to have been purely volcanic in origin.

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