90 Mr. Lyell on a recent Formation of 



ing covered by clay, would shrink considerably ; while the marl would not 

 contract, — or if at all, not in the same proportion. The author of this memoir 

 has himself had occasion to witness, in the moss of Kinnordy in Forfarshire, 

 the remarkable degree in which peat shrinks, when the quantity of its water is 

 diminished. In that Moss, the peat, since its drainage, has in many parts lost 

 by subsidence half its original thickness. 



The Test flows more rapidly than most of the rivers in the South of Eng- 

 land. Its water is very clear, and remains so during the highest floods. Prom 

 its sources to the north of Whitchurch and Andover, until it arrives near Brook, 

 about four miles and a half above Ashley Meads, where the marl occurs, it 

 flows through a district of chalk. After leaving the chalk, it enters the plastic 

 clay formation. In the muddy deposits formed in the slow-running parts of 

 the river, the exuviae of testacea are very abundant. The river is not known 

 to deposit calcareous matter any where at present, either in its channel, in the 

 ditches and drains, or in the meadows, during floods. Calcareous marly matter 

 has never yet been found in this neighbourhood unaccompanied by shells. 



Appendix I. 



On the Chara, and on its Seed-vessel, the Gyrogonite. 



For all that is valuable in the botanical remarks that occur in the present 

 Appendix on recent and fossil Charae, I am indebted to the assistance of Mr. 

 Brown and Mr. James De Carle Sowerby. 



M. Leman, in a notice published in the Nouv. Bulletin des Sciences, tom.iii. 

 No. 58. p. 108. for 1813, first identified the Gyrogonite with the seed-vessel 

 of some unknown species of Chara. He has remarked also, in the same me- 

 moir, "that the gyrogonites are sometimes accompanied by small irregular 

 tubes whose coats (parois) are also tubular, and whose central cavity is trans- 

 versely striated ; that the structure is identically the same with that of the 

 stems or branches of Charae, particularly of C. vulgaris and of C. tomentosa*." 

 M. Brongniart has figured one of these fossil stems ; but the transverse striae 

 in the central cavity (or rather septa, as they are there represented) which are 



* Ann. du Mus. d'Hist. Nat. torn. xv. PI. XXIII. fig. B. copied in Journ. des Mines, 

 torn, xxxii. PI. VIII. 



