The projecting ledges of bluestone that have horizontal seams form half
caves from the falling apart of the lower layers of the cliff caused by
rain and ice and often aided by the fine roots of the black birch, rock
oak, and other plants, until nature has worked long enough as a quarry-man
and produced half caves large enough to shelter a stooping man (Figs. 8,
9, and 10).
Although not always necessary, it is sometimes best to make a shelter for
the open face of such a cave, even if we only need it for a temporary camp
(Fig. 10); this may be done by resting poles slanting against the face of
the cliff and over these making a covering of balsam, pine, hemlock,
palmetto, palm branches, or any available material for thatch to shed the
rain and prevent it driving under the cliff to wet our bedding.