EXPLANATION OF PLATE 56. 91 



coast of Northumberland. This fragment is about 

 five feet high, and two feet three inches in diameter 

 at its base.* Scale one-twenty-fourth. (Sopwith.) 



2. Fragment of the bark on the trunk of a Sigillaria, 

 from Earl Fitzwilliam's coal-mine at Elsikar, near 

 Rotherham. In this mine many large trunks are 

 seen inclined in all directions, and some nearly ver- 

 tical. (See V. I. p. 353, Note.) The bark is converted 

 into a thin lamina of coal, and remains attached to 

 the lower portion of this specimen. It exhibits on 

 its outer surface scars formed by the articulations 

 of the bases of leaves; these are penetrated near 

 their centre by three apertures for vessels that 

 passed from each leaf into the trunk. The decorti- 

 cated upper part of this specimen presents an im- 

 pression of its striated internal surface, and exhibits 

 beneath each scale two oblong parallel apertures, 

 through which the vessels from a leaf penetrated 

 the trunk. Scale one-half. (Original.) 



The substance of the trunk must have been in a 

 state of decay, before the mud, which is now har- 

 dened into shale, could have entered the interior of 

 the bark. When trunks of this kind are inclined 

 at an angle exceeding 45°, they are usually dis- 

 tended with sandstone, or sandy shale; when at a 

 less angle than 45°, they are most commonly com- 

 pressed, and have only a thin flat portion of shale, 

 formed of indurated mud within their bark. The 

 bark, wherever it has not perished, is converted to 

 coal. 



2'. Articulating leaf-scar on the exterior of the bark of 

 another large trunk of Sigillaria from Elsecar. Nat. 



* M. Ad. Brongniart found a stem of Sigillaria in a coal-mine at 

 Essen in Westphalia, which was dichotomous near its top. 



