This species was founded on specimens from the Wealden beds of Sussex[443], but numerous examples of Chara ‘fruits’ and stems have long been known from the uppermost Jurassic rocks of the Dorset coast and the Isle of Wight, which may probably be included in this species. These fossil Charas are abundant[444] in the Chert beds of Purbeck age seen in the cliffs near Swanage. Pieces of corticated stems from this locality are represented in fig. 45 A and B.
The cortical cells surrounding a large internodal cell are very clearly seen in the section shown in fig. 45 B, and in the longitudinal view in fig. 45 A. The resemblance of these specimens to the stems of recent Stoneworts is very striking.
Fig. 47. Chara Knowltoni, Sew. × 30.
The single oogonium of fig. 47 was found in the Wealden beds near Hastings.
3. Chara Wrighti, Forbes. Fig. 46, d and e.
This species is characterised by globular or somewhat elliptical oogonia, with six or seven spiral bands.
It is very abundant in the Lower Headon beds of Hordwell Cliffs on the Hampshire coast[445]. Various species of Chara are commonly met with in the Oligocene beds of the Isle of Wight and Hampshire, as well as in the Paris basin beds, and elsewhere. Well preserved ‘fruits’ and stem fragments are met with in a siliceous rock of Upper Oligocene age imported from Montmorency in the Paris basin, and used as a stone for grinding phosphates at some chemical works near Upware, a few miles from Cambridge.
Many other species of fossil Charas are known from various horizons and localities, but the above examples suffice as illustrative types. In Post-Tertiary deposits masses of Chara and plant fragments occasionally occur forming blocks of Travertine. Examples of such Chara beds have been recorded by Sharpe from Northampton[446], by Lyell[447] from Forfarshire, and by other writers from several other districts. Beds of calcareous marl are occasionally seen as whitish streaks in the peat of the Fenland[448]; these often consist in great part of Charas. A season’s growth of Chara in a shallow lake or mere in the Fens may appear as a white line in a section of peaty and other material which has been formed on the site of old pools or lakes.
The recognition of specific characters in the isolated Chara ‘fruits’ usually met with in a fossil state is exceedingly unsatisfactory; the features usually relied on in the living species are not preserved, and great care should be taken in the separation of the various forms.