566 



IMBEDDING OF AQUATIC SPECIES 



[Ch. XLVIII. 



the shells are of a size whicli indicates tlieir having attained 

 a state of maturity. The shells are sometimes entirely de- 

 composed, forming a pulverulent marl ; sometimes in a state 

 of good preservation. They are frequently intermixed with 

 stems of Charse and other aquatic vegetables, the whole being 

 matted together and compressed, forming laminge often as 

 thin as paper. 



Fossilised seed-vessels and stems of Ghara.— 



of different eras, 



■As the Chara is 

 sil in formations 



much im 



geologist in characterising entire groups of strata, I shall 

 describe the manner in which I have found the recent species 

 in a petrified state. They occur in a marl-lake in Forfarshire, 

 enclosed in nodules, and sometimes in a continuous stratum 

 of a kind of travertin. 



Pig. 140. 



« 



i 



e 



3 



J 



Seed-vessel of Chara hispida. 



a. Part of the stem with the seed-vessel attached, Magnified. 



b. Natural size of the seed-vessel. 



c. Integument of the Gyrogonite, or petrified seed-vessel of Chara Mspida, found in the Scotch 



marl lakes. Magnified. 



d. Section showing the nut within the integument. 



e. Lower end of the integument to which the stem was attached, 



/. Upper end of the integument to which the stigmata were attached. 

 g. One of the spiral valves of c. 



The seed-vessel of these plants is remarkably tough and 

 hard, and consists of a membranons nut covered by an integu- 

 ment [dy fig. 140), both of which are spirally striated or 

 ribbed. The integmnent is composed of five spiral valves, of 



f 



