28 PETRIFACTIONS AND THEIR TEACHINGS. CHAP. I. 



but one genus, the common species of which (Eq. fluviatile) 

 abounds in marshy tracts, and on the banks of our ditches 

 and rivers. It has a jointed stalk, encircled by elegant 

 cylindrical dentated sheaths, and garnished with verticillate 

 linear leaves. In a fossil state several species of this genus 

 are known, of which there are specimens in Case A. Those 

 of the Equisetum Lyellii, from Pounceford in Sussex, were 

 collected by the Author in 1825. This species is peculiar to 

 the Wealden deposits; it has a cylindrical and articulated 

 stem, the articulations of which are embraced by regularly 

 dentated sheaths. It was a slender elegant plant, of the 

 proportions of the common existing Mare's- tail. 1 



EQUISETITES. Case E. These are the stems of gigantic 

 equisetaceous plants, which, though allied by their general cha- 

 racters to the diminutive existing Equisetum, differ in some 

 essential particulars. They are named by M. Brongniart, the 

 eminent botanist, Equisetites. These stems are from twenty 

 to thirty feet in height, and from ten to fourteen inches in 

 diameter. The surface is smooth, not striated, and is not im- 

 pressed by the denticulations of the sheath, as in the Mare's- 

 tail. The fructification is unknown. These plants, of which 

 there are many specimens in Case B. (of Eq. columnare, Eq. 

 later ale, &c.), are common in the inferior oolite of Yorkshire, 

 and are frequently discovered in an upright position. Exten- 

 sive areas covered by the roots and erect stems, apparently 

 occupying the spots where they originally grew, have been 

 laid bare in the Cleveland Hills. A few freshwater bivalves 

 are the only fossil-shells observed'in the laminated sandstone 

 in which the stems are imbedded. 



CALAMITES. Case , Upper Shelves. These large stems 

 belong to a tribe of plants which abounded in the carboni- 

 ferous epoch, and must have constituted an impdrtant fea- 

 ture in its flora, for their remains are abundant in the coal 

 deposits of every country. * Though bearing a general re- 

 semblance to the Equisetacese, they are entirely distinct; 

 their stems are articulated and regularly striated, and some- 

 times arborescent; the articulations are in general marked 

 with annular depressions, and studded with tubercles; in 



1 Pounceford, near Burwash, in Sussex, is an interesting locality of 

 the Wealden. See " Geology of the South-Eabt of England," p. 221. 



