COAL MEASURES. 



127 



casionally, also, a narrow coal seam can be observed, and vegetable 

 remains, such as Calamites, are not uncommon. In an outcrop 

 east of the Jackson Pottery the sand rock is locally bent into serpen- 

 tine curves, as if the ledges had been corrugated by some force 

 pushing sideways on them before they were fully indurated. The 

 outcrop is capped by heavy masses of boulder drift and clay, and at 

 the foot of the sand rock the clay pits of the pottery are opened. 



The shale beds below the sand rock are usually of a dark, blackish, 

 silky, shining color, partly hard and slate-like, partly soft and very 

 fissile. They contain a species of Lingula, and often also com- 

 pressed shells of Lamellibranches, besides trunks of Stigmaria, Sig- 

 illaria, and Lepidodendron transformed into iron pyrites. Nodules 

 of kidney ore are abundantly intermingled with the shales. 

 Interstratified with the latter there is frequently found a fine- 

 grained, argillaceous sand rock, called fire-clay by the miners, in 

 which trunks and leaves of Stigmaria are almost always plenti- 

 fully inclosed. Some of the stems are found covered with leaves 

 radiating in all directions, as if the apex of a branch had been im- 

 mersed in the liquid clay paste without any disturbance or com- 

 pression of the expanded leaves. The leaves are long and band- 

 like, flat at the outer part, subcylindrical, clavate, and connected at 

 the basal ends with the stems. 



The coal of the Jackson mines is bituminous, of a strong, resinous 

 lustre, with delicate laminar striation parallel with the bedding. 

 Split open in this direction, it presents a mottled structure ; a part of 

 the mass is a shining, amorphous bitumen ; another part is porous, 

 with the vegetable structure of charcoal. It breaks vertically with a 

 smooth, shining cleavage, with nearly square angles. Compressed 

 stems of Lepidodendron and Sigillaria can often be recognized in 

 the mass, either transformed into bitumen or preserved by a mould 

 of iron pyrites. A seam of iron pyrites is found almost invariably 

 interstratified with the coal, but can be readily separated ; the re- 

 mainder of the coal is not contaminated with an unusual propor- 

 tion of the pyrites, still the quantity is large enough to render it 

 unfit for blacksmith's purposes. The iron pyrites of the mines 

 can be sold to advantage for a price equal to that of the coal, to the 

 sulphuric-acid manufactory at Jackson. The heat-producing quali- 

 ties of the coal, for boiler use, etc., are excellent ; it burns with a 

 bright flame, leaving a small residuum of ashes. Its tendency 



