of the South Wales Coal-field. 493 



beds, are not so likely to become exposed in them ; whereas the operations of exten- 

 sive collieries naturally afford the opportunity of making vast collections from the un- 

 derclays ; for when a coal-seam is either throughout or partially too thin to permit 

 the excavation of the coal without the removal of some portion of the ground in 

 juxtaposition to it, the superior softness of the floor induces the miner to make the 

 required cuttings in it rather than in the ceihng ; or when it becomes necessary to 

 obviate the effects of a " creep" in any of the roads, it is again the floor that is 

 pared down, and in these and other ways a large amount of specimens in the 

 underclays is exposed. Sometimes however the ceiling of one coal-seam is the 

 floor of another, and in such instances, if the collector were on the lower bed, he 

 might discover above him specimens that would appear to contradict what is above 

 stated as a general rule, while it is obvious, an attentive examination of the case 

 would only confirm the truth of it. That bare stems or branches of Stigmaria 

 have been found in other beds there can be no reasonable doubt, indeed it would 

 be very surprising if many such instances did not occur ; for even if the underclay 

 were the natural and original site of the plant, specimens must have been occa- 

 sionally washed out of their first position and deposited in some superior bed at 

 the time of forming. 



The Stigmaria Ficoides is described by all those who have written on the 

 subject as the most abundant plant of our carboniferous series ; but no one has 

 given a fuller account of the localities in which it is found, of the external bota- 

 nical character it bears, and of the attitude it generally presents in situ, than Mr. 

 Steinhauer in the American Philosophical Transactions ; and his description is so 

 applicable to the condition of the plant in coal strata, which for the last seven 

 years have been the constant object of my own investigation, that I shall quote a 

 part of his description*. (New Series, vol, i. p. 265 et seq. 1818.) 



He says, " It is most abundant in the fine-grained siliceous stone provincially called Calliard and Gan- 

 nister, and in some of the coal-binds or crowstones. It is rather less frequent in the beds of scaly clay, 

 or clay mixed with siliceous sand and mica ; very common but completely compressed in the coal-shales 

 or bituminous slate-clay ; of occasional occurrence in the argillaceous ironstone ; not rare in the com- 

 mon grit and upper thick beds of argillaceo-micaceous sandstone or rag ; and sometimes, though rarely, 

 discoverable in the coal itself." — " The most perfect form in which this fossil occurs is that of a cylin- 

 der more or less compressed, and generally flatter on one side than the other. Not unfrequently the 

 flattened side turns in so as to form a groove. The surface is marked in quincuncial order with pus- 

 tules, or rather depressed areolae, with a rising in the middle, in the centre of which rising a minute 

 speck is often observable. From different modes and degrees of compression, and probably from dif- 

 ferent states of the original vegetable, these areolae assume very different appearances ; sometimes run- 



* Notwithstanding the closeness with which Mr. Steinhauer must have examined the Stigmaria beds, 

 the unvarying relation of the coal-seams to them does not appear to have struck him. — March 184'2. 

 VOL. VI. SECOND SERIES. 3 S 



