The casts of branches, rhizomes, tubers, buds and cones enable us to form a fairly exact estimate of the size and general appearance of this largest fossil Horse-tail. The Strassburg Museum contains many good examples of this species, and a few specimens may be seen in the British Museum. In the École des Mines, Paris, there are some exceptionally clear impressions of cones of this species from a lignite mine in the Vosges. It is estimated that the plant reached a height of 8 to 10 meters, about equal to that of the tallest recent species of _Equisetum_, but in the diameter of the stems the Triassic plant far exceeded any existing species. It is interesting to determine as far as possible, in the absence of petrified specimens, if this Keuper species increased in girth by means of a cambium. There are occasionally found sandstone casts of the pith-cavity which present an appearance very similar to that of Calamitean medullary casts[510]. The nodes are marked by comparatively deep constrictions, which probably represent the projecting nodal wood. The surface of the casts is traversed by regular ridges and grooves as in an ordinary Calamite, and it is probable that in _Equisetites arenaceus_, as in _Calamites_, these surface-features are the impression of the inner face of a cylinder of secondary wood (_cf._ p. 310). Excellent figures of this species of _Equisetites_ are given by Schimper in his Atlas of fossil plants[511], also by Schimper and Koechlin-Schlumberger[512], and by Schoenlein and Schenk[513]. 5. _Equisetites columnaris_ Brongn. Figs. 11 and 58, _B_. This species, which is by far the best known British _Equisetites_, was founded by Brongniart[514] on some specimens from the Lower Oolite beds of the Yorkshire coast. Casts of stems are familiar to those who have collected fossils on the coast between Whitby and Scarborough; they are often found in an erect position in the sandstone, and are usually described as occurring in the actual place of growth. As previously pointed out (p. 72), such stems have generally been deposited by water, and have assumed a vertical position (fig. 11). Young and Bird[515] figured a specimen of this species in 1822, and in view of its striking resemblance to the sugar-cane, they regarded the fossil as being of the same family as _Saccharum officinarum_, if not specifically identical. A specimen was described by König[516] in 1829, from the Lower Oolite rocks of Brora in the north of Scotland under the name of _Oncylogonatum carbonarium_, but Brongniart[517] pointed out its identity with the English species _Equisetites columnaris_.