Columnar structures in limestones are rare, and the type described in the present paper appears to be new to geologic literature. Buttress structures in volcanic plugs have escaped the notice of geologists, and the name is applied under the supposition that they have not been described. The two structures are unrelated save in having been formed by differential vertical movements.

The field observations were made by Branson and were too limited to satisfy some of the questions raised in preparing the article. Branson was in northwestern New Mexico for about six months and studied many of the igneous plugs of that region, some of them several times. The columnar limestone was observed in situ in only one place, and Branson visited that place only four times. The laboratory study of the limestone columns was made by Tarr and the explanation of their origin grew, largely, out of his previous . . .

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