92 Mr. Lyell on a recent Formation of 



nite, which was first used, when the true nature of these bodies was unknown, 

 to express the fossil or mineralized state of the pericarpium of Chara. The 

 gyrogonite, which occurs in the rock-marl of the Bakie, consists in general of 

 the empty integument completely replaced by carbonate of lime. (See PI. XII. 

 fig. 1. a,b, c, d, g, h.) Sometimes, however, the nut is found within, as a flex- 

 ible, brown membrane, not fossilized. (See PI. XII. fig. 1, e,f.) In the an- 

 cient gyrpgonites, as was before observed, the nut, as well as the integument, 

 is sometimes replaced by the substance of the matrix*. (See PI. XIII. fig. 2. b.) 

 In the Bakie gyrogonite, as in the ancient ones, the spiral valves are easily se- 

 parable. (See PI. XII. fig.l. g.) This gyrogonite, as well as the accompanying 

 stemSj was found upon a careful comparison to agree with C. hispida. The 

 fossil represented in PI. XII. fig. 1. a., will appear larger than its recent ana- 

 logue, PI. XII. fig. 2. a. : but this arises from the difficulty of procuring a ripe 

 specimen of the recent seed-vessel ; as in that state they fall off readily from 

 the plant. The stems fossilized in the rock-marl are sometimes empty (see 

 PI. XII. fig. I. m.), but more frequently they are filled with carbonate of lime. 

 C. hispida. — Chara hispida abounds at present in the Bakie Loch, and in 

 other lakes in Forfarshire. It contains so much carbonate of lime in its ve- 

 getable organization, and independently of calcareous incrustation, as to ef- 

 fervesce strongly with acids when dried. Each of the 5 spiral valves of the 

 seed-vessel turns rather more than twice round the circumference, the whole 

 together making between 10 and 11 rings. The number of these is very con- 

 stant. (See PI. XII. fig. 2. a, b.) The stems of C. hispida are longitudinally 

 striated, with a tendency to be spiral. These striae (as appears to be the case 

 with all CharaB) wind round in a contrary direction to the spiral valves of the 

 pericarpium (see PI. XII. fig. 2./, g.) : i. e. the striae of the stems turn al- 

 ways like the worm of a screw, from right to left, (as is the case with the Con- 

 volvulus and the Helicteres (see PI. XII. fig. 5.) ; the valves of the capsule turn 

 from left to right (as is the case with the honey-suckle), a fact which, from the 

 figures of Charae given by botanists, appears not to have been attended to. 



* I find that some specimens of gyrogonite (C. helicteres, Brongn.) which I collected in 1823, 

 when on a tour with M. C. Prevost, from a thin stratum of greenish argillaceous sand, of the up- 

 per freshwater formation in the Forest of Fontainbleau, allow the outer convex coat of the valves 

 to peel off, and leave what resembles the replacement of the nut within, very much as in C. Medi- 

 caginula of the Isle of Wight (PI. XII. fig. 2.), but not so firmly united. The integument in 

 these is very fragile, and the nut tender. Were the capsules imbedded in a more compact matrix, 

 the nuts would probably be easily extracted. The stratum in which the above gyrogonites 

 abounded, was exposed in a quarry at " Les Rochers du Fort des Moulins," near Les Basses 

 Loges: beneath it was the Gres de Fontainbleau in situ. 



