704 



GEOLOGY. 



abundantly in the coal series, their stems are but rarely encountered. It is uncertain 

 to what tribe of plants the annexed specimens belong, denominated from the wedge and 

 ring-shape of their leaves, very abundant in many localities. 



Sigillarise. This is a class of trees, of which many species are enumerated, formerly 



supposed to be monocotyledonous plants, allied to the arborescent ferns, but now 

 considered to belong to the dicotyledonous tribe, differing from any now existing upon 

 the face of the globe. The name is derived from sigillum, a seal, and refers to the im- 

 prints upon the surface of the stem or trunk, as in the figure, 

 which are scars left by the separation of the stalks from it. 

 Longitudinal ribs or flutings marked the stem, a structure 

 exhibited by some living dicotyledonous trees in New 

 Zealand. Sigillarioe are often found crushed into slabs, by 

 the weight of the superincumbent strata, but vertical or 

 highly inclined trunks of these fossil trees have been 

 repeatedly discovered, standing apparently in the place 

 where they grew, the bark being converted into coal, with 

 the interior now filled up witli sand or clay ; and it is no 

 uncommon occurrence at present, in tropical countries, for 

 the interior of hard-wood trees to be entirely ate away by 

 insects, the bark being left intact, and the tree to all ap- 

 pearance sound. Brongniart long ago described a remarkable 



example in the Treuil coal-mine near Etienne, in the department of the Loire, of which 

 the figure is a view. The coal formation in this place offers a circumstance favourable for 



observation, being situated in such 

 a manner that it can be worked in 

 open day as a quarry, of which we 

 have no instance in England. The 

 mine presents a series of alternating 

 beds of schistose clay, ironstone, coal, 

 and micaceous sandstone, in which 

 numerous stems occur, placed ver- 

 tically, traversing all the strata, of 

 which the view annexed shows only 

 a very small proportion. It is a true 

 fossil forest, as it were petrified in 

 place. The stems, for the most part, 

 were observed to be cylindrical, 

 articulated, and striated, the interior 

 showing no organic texture, but 

 filled with a rock of the same nature 

 as that composing the beds traversed. 

 The occurrence of similar fossil 



trunks in the coal measures has been often noticed, some of which must have been of 

 gigantic size, the diameter of the remains varying from half a foot to three feet, and the 

 length extending to sixty feet and more. Our recent railway operations have brought 

 to light a considerable number of instances. In the construction of the Clay cross tunnel, 

 which runs through strata lying in the middle of the Derbyshire coal measures, a group 

 of between thirty and forty trees was discovered, standing close together, at right angles 

 to the plane of the strata ; and in forming the Manchester and Bolton railway, five 

 trunks were found, of which an excellent memoir has been given by Mr. Hawkshaw, from 



Section of a Coal-mine near Etienne. 



