Mineralogy and Geology. 425 
the pith-cylinders of many coal-formation trees became divided in the 
ed of growth. These fossils are most abundant in the Upper coal 
m ation, but occur also in the Middle coal formation. The following 
Varieties may be distinguished : 
_ (a) Var. approzimata, with fine uniform transverse wrinkles. This 
ls usually invested with a thin coating of structureless coal. 
(6) Var. angularis, with coarser and more angular transverse wrinkles, 
This is the character of the pith of Dadozylon. 
(°) Var, distans, usually of small size, and with distant and irregular 
Wrinkles, is is sometimes invested with wood having the structure of 
Calamodendron, and perhaps is not generically distinct from pprox- 
tmatum, 
(¢) Var. obscura, with distinct and distant transverse wrinkles, but not 
strongly marked on the surface. This is the character of the pith eylin- 
ders of Sigillaria and Lepidophloios. : 
Expocenrres, L. & H.—Many sandstone casts, answering to the char- 
acter of the plants described under this name by Lindley, oceur in 
the Upper coal formation. They are sometimes three inches in diameter 
and several feet in length, irregularly striate longitudinally, and invested 
Neoaly matter. Sometimes they show transverse stration in parts 
their length, I believe they are casts of pith cylinders of the nature of 
“tnverga, and probably of sigillaroid trees. 
ses, L. 3 —Phhnts of this kind are found in the sandstones 
the ree coal formation of the Joggin 
