Of the land-surfaces of the Cambrian period we know nothing; and there is, therefore, nothing surprising in the fact that our acquaintance with the Cambrian vegetation is confined to some marine plants or sea-weeds, often of a very obscure and problematical nature.  The “Fucoidal Sandstone” of Sweden, and the “Potsdam Sandstone” of North America, have both yielded numerous remains which have been regarded as markings left by sea-weeds or “Fucoids;” but these are highly enigmatical in their characters, and would, in many instances, seem to be rather referable to the tracks and burrows of marine worms.  The first-mentioned of these formations has also yielded the curious, furrowed and striated stems which have been described as a kind of land-plant under the name of Eopkyton (fig. 28).  It cannot be said, however, that the vegetable origin of these singular bodies has been satisfactorily proved.  Lastly, there are found in certain green and purple beds of Lower Cambrian age at Bray Head, Wicklow, Ireland, some very remarkable fossils, which are well known under the name of Oldhamia, but the true nature of which is very doubtful.  The commonest form of Oldhamia (fig. 29) consists of a thread-like stem or axis, from which spring at regular intervals bundles of short filamentous branches in a fan-like manner.  In the locality where it occurs, the fronds of Oldhamia are very abundant, and are spread over the surfaces of the strata in tangled layers.  That it is organic is certain, and that it is a calcareous sea-weed is probable; but it may possibly belong to the sea-mosses (Polyzoa), or to the sea-firs (Sertularians).

Amongst the lower forms of animal life (Protozoa), we find the Sponges represented by the curious bodies, composed of netted fibres, to which the name of Protospongia has been given (fig. 32, a); and the comparatively gigantic, conical, or cylindrical fossils termed Archoeocyathus by Mr Billings are certainly referable either to the Foraminifera or to the Sponges.  The almost total absence of limestones in the formation may be regarded as a sufficient explanation of the fact that the Foraminifera are not more largely and unequivocally represented; though the existence of greensands in the Cambrian beds of Wisconsin and Tennessee may be taken as an indication that this class of animals was by no means wholly wanting.  The same fact may explain the total absence of corals, so far as at present known.

[Illustration:  Fig. 29.—­A portion of Oldhamia antiqua, Lower Cambrian, Wicklow, Ireland, of the natural size. (After Salter.)]

The group of the Echinodermata (Sea-lilies, Sea-urchins, and their allies) is represented by a few forms, which are principally of interest as being the earliest-known examples of the class.  It is also worthy of note that these precursors of a group which subsequently attains such geological importance, are referable to no less than three distinct orders—­the Crinoids or Sea-lilies, represented by a species of Dendrocrinus; the Cystideans by Protocystites; and the Star-fishes by Palasterina and some other forms.  Only the last of these groups, however, appears to occur in the Lower Cambrian.