rn-like type
seem to have been comparatively common during the times of the Oolite.
On the other hand, the Cycadaceae manifest close relations to the
conifers. Both have their seeds originally naked; both are cone-bearing;
both possess discs on the sides of their cellules; and in both, in the
transverse section, these cellules are subhexagonal, and radiate from a
centre. Such were the very curious relations that united into one great
sept the prevailing members of the Oolitic flora; and similar bonds of
connection seem to have existed in the floras of the still earlier ages.

[Illustration: Fig. 149.

IMBRICATED STEM.

(_Helmsdale._)]

[Illustration: Fig. 150.

(_Helmsdale._)]

[Illustration: Fig. 151.]

In the Oolite of Scotland I have, however, at length found trace of a
vegetable organism that _seems_ to have lain, if I may so express
myself, outside the pentagon, and was not a member of any of the great
families which it comprised. (See Fig. 151.) I succeeded about four
years ago in disinterring from the limestone of Helmsdale what
_appears_ to be a true dicotyledonous leaf, with the fragment of another
leaf, which I at first supposed might have belonged to a plant of the
same great class, but which I now find might have been a portion of a
fern. When _Phlebopteris Phillipsii_ was first detected in the Oolite of
Yorkshire, Lindley and Hatton, regarding it as dicotyledonous,
originated their term Dictyophillum as a general one for all such
leaves. But it has since been assigned to a greatly lower order,--the
ferns; and Sir Charles Lyell has kindly shown me that an exotic fern of
the present day exhibits exactly such a reticulated style of venation as
my Helmsdale fragment. (See Fig. 152, p. 497.) The other leaf, however,
though also fragmentary, and but indifferently preserved, seems to be
decidedly marked by the dicotyledonous character; and so I continue to
regard it, provisionally at least, as one of the first precursors in
Scotland of our great forest trees, and of so many of our flowering and
fruit-bearing plants, and as apparently occupying the same relative
place in advance of its contemporaries as that occupied by the conifer
of the Old Red Sandstone in advance of the ferns and Lycopodaceae with
which I found it associated. In the arrangement of its larger veins the
better preserved Oolitic leaf somewhat resembles that of the buckthorn;
but its state of keeping is such that it has failed to leave its