History of our Coalfields.

On Wednesday evening at a meeting of the Doncaster Microscopical and General Scientific Society, Mr. Ballinger read a paper on “The history of our Coal Fields.”

In the course of his introductory remarks Mr. Ballinger said it was not his intention to speak of the modern history of coal, but of its ancient history, and to tell them how and why it became coal and the reason why there was coal in one part of the country and not in another.

It was certain that coal was the result of a large deposition of vegetable matter. Of all things found, fossil ferns were the most beautiful and the most interesting. The ferns of the coal period were very numerous and included both herbaceous forms like the majority of existing species and arborescent forms similar to the large tree ferns of New Zealand. The tissues of those ferns were always found to be converted into true coal. Coal consisted almost entirely of carbon.

The only way in which they could conceive of large deposits of carbon taking place was by accumulation of vegetable matter. Coal was composed of successive thin layers, differing slightly in colour and in texture. By cutting thin and transparent slices of coal they were able by means of the microscope to ascertain not only that the carbon was derived mainly from vegetables, but in many cases to find out what kinds of plants and what parts of them entered into the formation of coal. Coal occurred in beds of varying thicknesses and following no regular order beyond the intermixing of beds of clay and sandstone.

The millstone grit, the great series of beds immediately below the coal measures, and which in Britain were from 1000 to 3000 feet in thickness were deposited in a shallow sea, not far from the shore. It was accepted beyond dispute that all rocks, with the exception of the igneous, which were the result of volcanic action. Had at some remote period been deposited at the bottom of the ocean in the form of fine sediment. In the River Don, after a heavy storm, they would see the water was of a dull, dirty colour. If they would take a bucket full of it and let it stand for a day they would find a thin layer of mud had settled at the bottom of the bucket, which clearly proved that something beside water was carried down the channel of the river – in fact, fine mud and sand, collected from the land over which the water had flowed, was carried down as well. What became of it; it must find its way somewhere.

It was borne along the river channels as long as the current which bore it lasted, but when the current ceased the sediment fell to the bottom, as it did in the case of the bucket of water. The current of the river lost itself in the sea and the sediment was consequently deposited in the sea. Some of it was deposited in the calmer parts of the river, and hence the sand banks which they often saw in river beds. That was how the millstone grit was laid down in the bed of a shallow sea. In course of time the sea in which the millstone grit was deposited became entirely filled up, or it might have been upheaved by volcanic agencies and began to appear as dry land. A fine layer of mud accumulated on the land which had taken the place of what had been sea.

It was still only a flat marshy place, lying close to the sea shore. By the bye, vegetation took root and flourished with a luxuriance which the special conditions of the time induced. The vegetation flourished and died, and its place was taken by other. The leaves, seeds, fruits, stems, and fallen trunks of vegetation gradually accumulated. The land then gave place to the sea again, and again the shallow sea became filled up with sediment, or was upheaved by volcanic agency, and land appeared as before. The vegetation started again and the old condition of things repeated. They had two beds of interstratified clay, or shale, two beds of coal, and one bed of sandstone. The process continued again and again many times until at length a complete change came. The conditions changed.

The volcanic influences, of which there were many traces in the coal measures, gained the ascendancy. The land, which had been a marshy plain, rose in some places, sank in others, and a new order of things came in. The old sandstone period had begun, the coal period was at an end. How could they know for certain that that under-clay was the soil in which the coal grew, and that the land sank beneath the sea and rose again? The fossil stigmaria, had been proved to be not a distinct fossil tree but the roots of a tree called Sigillaria very common at the coal period.

The Sigillaria grew in the under-clay; its roots were fossilised there, whilst the upper part of the tree went to aid in the formation of coal. That put it beyond a doubt that the under-clay was the soil in which the coal vegetation grew. The animal remains discovered were all of the kinds which existed on land. Reptiles had left traces of their existence. Scorpions, very similar to those living at the present day, beetles, and Dr. Dawson investigated in Canada a large trunk of Sigillaria which was found with sandstone.

It was suggested by Sir Charles Lyell that as the trunk was standing upright in the bed of coal it was extremely probable that in the old days it was the hollow stump of a tree, and if so, that in that day as at present the hollow trunks of trees formed a trap for small creatures to fall into and die. So Dr. Dawson investigated the fossil trunk of a tree, and found a small worm which was scarcely to be distinguishable from the living centipedes. That to his mind was strong evidence that the coal was formed on the land and not collected as “drift” in the ocean.

He next spoke of the different kinds of coal, commencing with the Bituminous, which he said consisted of a large number of little bodies more or less rounded, which lay inside larger bodies – the inner body being the minute spores or seeds and the outer the cases which enveloped them. Mr. Carruthers had come to the conclusion that the seeds were those of a plant very nearly allied to the modern club moss. The little moss which grew so freely on the higher mountains of England and throughout the world bore precisely the same kind of fruit as that of which the bituminous coal was made. Another agent from which the materials of the bituminous coal had been derived was like the modern club moss in New Zealand. The coal of the Yorkshire coal field was bituminous, and of the very soft, free-burning kind. The next section of coal was called Authracite.

It was found in the South Wales, Forest of Dean and Bristol coal fields. In those coal fields the coals, sometimes the very same bed, gradually changed from the bituminous to the authracite varieties. Authracite coal was a coal which had been changed or acted upon by the internal heat of the earth in a greater degree than ordinary coal. It was usually occurred in coal fields were the strata had been much disturbed and contorted, and the same internal heat which produced the contortion of the surrounding rocks must have had some influence upon the beds of coal which those rocks contained. The authracite coal was very hard, burned a long time, gave out a great heat, as might be expected from the fact that it contained about 90 per cent of carbon. There were other sub-divisions of coal, such as cannal coal, parot coal, steam coal, etc., but they were all included in the two great classes of coal which he had described. He then mentioned several of the fossils from the coal measures, and said of the plants that were commonly presented to them ferns seemed to take the lowest class, and conifers the highest, The ferns were most prolific, occurring in vast quantities in the shales which overlaid the coal seams. There appeared to have been an uniformity in the vegetation of the coal period to which there was now no parallel. Perhaps the most inexplicable phenomenon was the occurrence of coal in the artic regions.

In conclusion Mr. Ballinger stated that under the microscope were a series of slides of coal and fossil woods, and on the table a collection of coal, kindly lent by Mr. Bridge, the courteous manager of the Doncaster Corporation Gas Works.