44 PETRIFACTIONS AND THEIR TEACHINGS. CHAP. I. 



constitute the deposits termed coal-measures, were accumu- 

 lated. Every coal-field (as a group of these strata is generally 

 termed) is composed of a succession of a triple series of 

 beds ; viz. firstly, the lowermost : a tough argillaceous 

 earthy stratum, termed under-clay, on which the bed of coal 

 invariably rests; and it is in this deposit that the roots 

 (Stigmaria3) of the trees are always found, and commonly 

 parallel with the pkne of the strata ; these are generally the 

 only vegetable remains contained in this bed, though the clay 

 is occasionally black from an intermixture of carbonaceous 

 matter. Secondly, the coal, which is composed of the stems 

 and foliage of trees transmuted into a bituminous carbon- 

 ized mass : large stems, branches, or leaves, are but seldom 

 found in it. Thirdly, the roof, or overlying stratum, con- 

 sisting of slaty clay, and water-worn detritus of other rocks 

 transported from a distance, and full of detached leaves, and 

 flattened and broken trunks and branches : it contains layers 

 and nodules of ironstone enclosing leaves, insects/ and crus- 

 taceans. In some localities beds of fresh-water shells as 

 mussels, in others marine shells, are intercalated : finely 

 laminated clays, micaceous sand, grit, pebbles of limestone and 

 sandstone, are sometimes imbedded in it. Thus it seems 

 probable that the under-clay is the natural soil in which the 

 coal-trees grew, the roots often remaining in their original 

 position and spreading out from the trunk : the coal is formed 

 of the carbonized stems and foliage ; and the roof, or upper 

 bed of shale and clay, is composed of the leaves and branches 

 of a forest that was overwhelmed and engulfed beneath an 

 accumulation of transported detritus. 1 



PSAROLITES or PsARONius. Cases C, D, E. Lower Shelves. 

 [3 to 5.] On these shelves is an extensive series of sili- 

 cified stems, many of them cut transversely and polished ; 

 the specimens labelled as above are chiefly from the Triassic 

 or New Red Sandstone deposits of Chemnitz, near Hillersdorf, 

 in Saxony. They are portions of petrified trunks of trees 

 allied to the arborescent ferns and club-mosses, and possess a 

 remarkable internal structure, that is exquisitely preserved in 

 many of the petrifactions before us. The transverse sections 



1 For a fall consideration of this subject see " Wonders of Geolo^v," 

 pp. 669, 718, 731 : "Pictorial Atlas of Organic Remains," p. 181. 



