Note 44 — Chapter III · ASCENSION.

In this case, and in that of the fissile pumice-stone, the structure is very different from that in the foregoing cases, where the laminæ consist of alternate layers of different composition or texture. In some sedimentary formations, however, which apparently are homogeneous and fissile, as in glossy clay-slate, there is reason to believe, according to D’Aubuisson, that the laminæ are really due to excessively thin, alternating, layers of mica.