FOSSIL PLANTS.
Cambrian Plants.—
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The oldest Australian plant-remains belong to the genus Girvanella. This curious little tubular unicellular organism, once thought to be a foraminifer, shows most affinity with the blue-green algae (Cyanophyceae), an important type of plant even now forming calcareous deposits such as the calcareous grains on the shores of the Salt Lake, Utah, and the pea-grit of the Carlsbad hot springs. Girvanella problematica occurs in the Lower Cambrian limestones of South Australia, at Ardrossan and elsewhere.
Silurian Plants.—
Amongst Silurian plants may be mentioned the doubtful sea-weeds known as Bythotrephis. Their branch-like impressions are fairly common in the mudstones of Silurian age found in and around Melbourne. They generally occur in association with shallow-water marine shells and crustacea of that period.
The genus Girvanella before mentioned is also found in the Silurian (Yeringian) of Lilydale and the Tyers River limestone, Victoria ([Fig. 54]).
