136 



THE POPULAR EDUCATOR. 



shall confine ourselves to geology proper, and not trespass upon 

 mining engineering. 



It ia needless to cite any proofs that coal owes its origin to 

 vegetable growth, more than to say that the microscope can 

 occasionally reveal the woody structure, and fossil trees are 

 frequently found in situ; hence there is no room for doubt. 



Moreover, a careful study of the different geological forma- 

 tions has furnished us with the history of the vegetable accu- 

 mulaiions from the present to the most remote eras. The peat 

 mosses represent the accumulations now in course of formation. 

 Digging down into the bog, with a little care, the different 

 plants may be separated from the decaying mass sufficiently to 

 distinguish them. A considerable change has passed over 

 them ; they have lost their colour and their suppleness, and are 

 dark, sometimes quite black and friable. Older still is the 

 brown coal of Germany. The form and structure of the plants is 

 yet capable of being discerned. But the lignite is more stone- 

 like than the peat. Deeper down and longer buried has been 

 the jet found in the secondary strata of Yorkshire and the 

 north of Scotland. This substance is again a step nearer the 

 true coal which the lower formations contain. 



Coal properly so called has been tho- 

 roughly submitted to the process of bitu- 

 menisation, as the peculiar change has been 

 termed. All these vegetable matters yield 

 to chemical analysis the same substances. 



The whole aspect of the carboniferous 

 period points to a time in which circum- 

 stances combined to cause the most rapid 

 vegetable growth. The depositions which 

 now form our coal-fields were made, not in 

 the deep sea, but in shallow estuaries. The 

 occurrence of " mussel-beds," as the miners 

 term accumulations of Modiola fossils ; the 

 fossils of batrachian-like reptiles, which 

 mast have lived partly upon land ; the hun- 

 dreds of species of ferns and other delicate 

 flora, whose leaves and stems give no evi- 

 dence of rough treatment, as if they had 

 been carried down by large rivers and de- 

 posited upon the bed of the ocean, all indi- 

 cate that the period of the coal deposit was 

 marked by vast low-lying marshy estuaries, 

 something like the Sunderbunds of India, 

 the thickly wooded Delta of the Ganges, or 

 the cypress swamps of America, if only they 

 were in connection with the sea. 



The flora, however, of the carboniferous 

 period differed considerably from that of a 

 forest such as is now found on the earth. 

 All the trees were almost wholly of the class 

 called endogenous; that is, as we explained 

 in a previous lesson, those whose growth 

 was from the interior, like the cane and 

 bamboo, and which therefore exhibit no 



rings of growth as the exogenous plants, the chief of our present 

 flora, do. These endogenous plants are capable of rapid growth, 

 and to this fact may probably be ascribed the vast accumula- 

 tion of vegetable matter which is fossilised in our own coal- 

 beds. We cannot imagine such accumulations to have been 

 formed of trees which required a long number of years for their 

 growth. Some of the trees of the carboniferous period belong 

 to the class of Conifers, which is the connecting link between 

 the endogens and the exogens. 



Some of the members of the carboniferous jungles we shall 

 now describe ; and by reference to our sketch of a coal forest, 

 an admirable idea of the flora of the period will be obtained. 



Tlie Sigillaria and the Stigmaria. The coal itself seldom 

 yields fragments of plants which can be recognised ; but imme- 

 diately underlying the seam of coal is a bed of shale, once the 

 soil in which the trees of the carboniferous forest grew. This 

 deposit yields abundance of vegetable remains. Most prominent 

 amongst these fossils is the Stigmaria, so called from the 

 punctures (stigma) wi,th which its surface is covered. It is a 

 roundisii stem, with forked branches at its extremity. Tor long 

 it was supposed to have been a water-plant, which, sinking to the 

 bottom, became covered frith the mud, and so fossilised ; but 

 now it has been proved that the stigmaria is the root of the 



9k SPHENOPTERIS CBBNATA. 95. PECOPTERIS 

 LONCHITICA. 96. NEUROPTERIS GIGANTEA. 



Sigillaria, a great tree which predominated in the forests of the 

 time. From the punctures these long flsshy roots gave off cellular 

 rootlets. This formation was precisely adapted to feed the great 

 succulent tree with large supplies of moisture. The tree was 

 very different from any we know. It rose up from fifty to eighty 

 feet with a branchless stem ; but near its top flourished a pro- 

 fusion of long slender leaves. The sigillaria was a true crypto- 

 gam, but only one specimen has been found in which the seed 

 was attached. The seed-lobes were roundish cases growing on 

 the enlarged stem of the leaves, and from the structure and 

 arrangement of the spores, the sigillaria has been proved to be 

 a near relation to the club-mosses. 



The Lepidodendron (lepis, a scale, and dendron, a tree) was 

 almost as numerous as the sigillaria. Although very different 

 in appearance, yet they are closely allied. The stem of the 

 sigillaria is fluted, but that of the lepidodendron is marked 

 regularly with lozenge-shaped whorls. It was almost as large 

 as its neighbour, but its seeds were something like the cones of 

 our fir-trees, and the top of the tree ramified into numerous 

 branches covered with short stumpy leaves. 



The Calamites were of a very different 

 appearance from any other plant of tha 

 forests, and as different from any tree of our 

 time. The stem was tall, smooth, and slen- 

 der, marked near the bottom with circles 

 of whorls or pits, from which had fallen the 

 leaves. The branches were given off in 

 rings round the stem, and they again bore 

 smaller twigs, arranged in a similar manner. 

 The fruit was developed at the end of the 

 branches, and agrees even to the most minute 

 particulars with that of the horse-tail. The 

 root of the calamite was pointed, not unlike 

 a carrot, but marked with regular whorls 

 where the rootlets had branched off. 



Of these three specimens of the faunti, 

 of the coal period were the forests of the 

 age chiefly composed. Their representatives 

 with us are very small and insignificant 

 plants; the club-mosses and horse-tails of 

 our marshes and ponds are the best known. 

 But in those days their relations were giants, 

 rivalling the highest of our forest trees. 

 The growth of this profuse vegetation must 

 have been very rapid, and the repeated 

 alterations of level of those low-lying marshy 

 forests frequently caused them to be sub- 

 merged and covered with a deposit of sedi- 

 mentary matter. No sooner, however, did 

 the waters drain off than up sprung another 

 jungle, to decay in its turn, and add its 

 quota to the forming coal-bsd. 



In examining the shales of the period, 

 the student will constantly find beautifully 

 preserved specimens of fern and other 

 leaves. The most common of these ferns are the Sphenopteris 

 (the wedge-fern, Fig. 94), the Pecopteris (comb-fern, Fig. 95), and 

 the Neuropteris (nerve-fern, Fig. 96). 



Of the animal remains yielded by the coal measures proper, 

 the first was discovered in 1844, in the coal of Minister- Appel, 

 in Rhenish Bavaria. It was a true reptile, nearly related to the 

 salamanders, and was named the Apateon pedestris. A few 

 years later the coal measures near Strasburg yielded three dis- 

 tinct species of air-breathing reptiles. The largest of these, the 

 Arcliegosaurus Decheni, was 3 feet 6 inches long. Its head 

 was triangular, like the crocodile, with large eyes ; its fins were 

 slender -more adapted for swimming than walking or crawling. 

 The American coal-fields, the very year of the discovery of the 

 Apateon, yielded slabs printed with the footsteps of some 

 lizard-like reptile ; but it was not until 1852 that any fossil of 

 these inhabitants of the coal-forests was discovered. 



The first osseous remains were obtained from the coal -fields 

 of America by Sir C. Lyell. The sigillarise are frequently 

 found standing erect. When they decayed, their inside gave 

 way, and they became hollow trunks. When the waters flooded 

 the forest, sand and mud filled the hollow tree, and consolidated 

 into a stone pillar dyed black with carbonaceous matter. These 

 pillars are much dreaded by the miners, as they frequently drop 



