318 



PALEOZOIC TIME. 



Even the solid anthracite has been found to contain vegetable tis- 

 sues. On examining a piece partly burnt, Professor Bailey found 

 that it was made up of carbonized vegetable fibres. The preceding 

 figures, 615 a, b, c, are from his paper on this subject. He selected 

 specimens which were imperfectly burnt (like Fig. 615 a), and ex- 

 amined the surface just on the borders of the black portion. Fig. 

 615 b represents a number of ducts, thus brought to light, as they ap- 

 peared when moderately magnified, and Fig. 615 c, two of the ducts, 

 more enlarged ; the black lines being the coal that remained after the 

 partial burning, and the light spaces silica. The ducts were one tenth 

 of a millimeter (about four thousandths of an inch) broad. Dawson re- 

 ports like results with bituminous coal. 



The spores (fruit-cellules) and the spore-cases (sporangia) of the 

 Lycopods (Lepidodendrids) abound in the coal, to such an extent, in 

 some places, that it has been suggested that mineral coal was made 

 mainly out of them. While, as Dawson has shown, this inference is 

 not sustained by facts, such spore-cases are still very common in most 

 coal. (The Lycopodium powder of the shops, used in fire works, on 

 account of its inflammability, consists of the spores of the common 

 species of the woods of Europe.) Fig. 616 represents, very much mag- 

 nified, the surface of a piece of Ohio bituminous coal, showing a frag- 

 ment of a spore-case and many of the spores. The spore-cases vary 

 in size, from a tenth to a hundredth of an inch ; and in the coal they 

 often have an amber-yellow color. Dr. Dawson states that he has a 

 specimen of Pennsylvania anthracite full of spore-cases, but that the 

 Pictou coal is remarkably free from them. 



5. Iron-ore Beds. — The iron ore of the Coal-measures is usually 

 in the form of concretionary masses, sometimes closely aggregated 

 into a bed from a few inches to three or four feet thick, and some- 

 times distributed through a shaly or calcareous layer, and often too 

 sparsely to be of economical value. The ore is generally the car- 

 bonate of iron, called siderite (or often spathic iron). It contains as 

 impurity ten to thirty per cent, or more of silica and other earthy 

 matters, and hence is called clay-ironstone. 



The concreting took place amid the sediments, and sometimes through silica; and 

 hence a portion of the sediments is included. Such ores are of a bluish-gray or drab 

 color, and are easily distinguished from other stones by the weight. In the Coal- 

 measures of Pennsylvania, according to Lesley, the most valuable layer for its iron 

 ore is the buhrstone bed, in the Lower Coal-measures, between the Coal-beds B and C 

 in the section on page 311 ; but at Johnstown, on the Conemaugh, the ore used at the 

 iron works is from a layer sixty feet above the Coal-bed E. No valuable deposits are 

 known in the anthracite region. 



Some of the clay -ironstone has the composition of limonite, or the hydrous oxyd of 

 iron; but, in general, the limonite beds have been made through the alteration of the 

 siderite (p. 58). Occasionally, the ore of the Coal-measures is hematite, or the red 

 oxyd of iron. 



