SIGILLARIA. 



•19 



given to these extinct trees, from the impressions appear- 

 ing as if made by a seal or die. These stems are generally 

 found broken to pieces, and when lying in a horizontal posi- 

 tion in the strata, are quite flat from the pressure of the 

 superincumbent deposits. 

 The stems vary from 

 a few inches to three feet 

 in circumference, and spe- 

 cimens have been disco- 

 vered that indicate a 

 length of sixty feet. They 

 often escape compression, 

 and stand perpendicularly, 

 intersecting the horizon- 

 tal strata, and having 

 roots proceeding from 

 the base. They are ge- 

 nerally surrounded by an 

 envelope, an inch in thick- 

 ness, of fine, crystalline, 

 bituminous coal. The lon- 

 gitudinal plaitings, which 

 are the characteristic 

 marks of the Sigillariae, 



Sandstone. 



Shale. 



MAIN COAL SEAM. 



are commonly indistinct Lign. i6i.— Stem of sigillama pacht- 



at the base. A Specimen DERMA J mthe JarrowCoal. Ten feet high, 



figured in the beautiful and highly interesting work of Dr. 

 Lindley and Mr. Hutton,* was ten feet high {Lign. 161), 

 and two feet in diameter at the base. Its roots were in shale, 

 immediately above the main bed of coal, and the trunk 

 extended through several strata of shale and sandstone. 



The upright stems almost always consist of sandstone 

 within the carbonized bark ; but one silicified specimen has 

 been discovered, by which M. Ad. Brongniart has been 

 * The Fossil Flora of Great Britain. 



