42 



COAL FORMATION. 



are often found, like alJ the rest of those of which we speak, con- 

 verted into argillaceous matter, which has hecome hard, or into car- 

 bonates of iron, but rarely into silicious matter. The external 

 vegetable tissue is frequently found to have passed into a carbonous 

 state. 



Fig. 42. Calami'tes suckomi. 



Fig. 43. Calami'tes cannafo'rmis. 



12. The Lycopodia'cesc embrace various species of Lepidode' n- 

 drons (Jigs. 44, 45), of which entire trees have been sometimes 

 found, upwards of sixty feet in height. Their trunks present 

 rhomboidal projections, spirally arranged, which clearly exhibit 

 near the top cica'trices of leaves. 



.Fig. 44. Lepidode' ndr on crena'lum. Fig. 45. Lepidode.' ndron e'legans. 



13. The Sigilla'rise (fig. 46) seem to range themselves next to 

 the Cyca'derc ; their stems, flattened by pressure, are channelled 

 lenpthwise but not articulated, and the cica'trices are arranged in a 

 longitudinal series. The stems, called stigma'ria (Jig. 47), are, 



11. What genera belonging to the family of equisita'ceae are found in 

 coal-beds ? 



12. What fossil plants of the family of lycopodia'ceffi are found in coal- 



measures ? 



