some water, and that occasionally little clouds of fine sand or silt were carried into that water, and likewise sank to the bottom in fine layers. I have no doubt of the process of accumulation being a very slow and gradual one, for I have long been accustomed to look upon the time required for the formation of any wide spread bed of stratified rock whatever, even a single foot in thickness, as one to be measured only by the lapse of scores of years, perhaps by that of centuries. Each bed of coal is certainly made up of thin laminæ, which are obviously laminæ of deposition, every tenth or every hundredth of an inch requiring a distinct period for its production, as in the case of all other laminated rocks. The variations that take place in the quality and character of coals, sometimes inch by inch in their different laminæ, one being less and another more earthy, &c., the separation of the laminæ by little films of shale, or by thicker "partings" of substances that are distinctly argillaceous earth, more or less mingled with carbonaceous matter, those partings occasionally thickening out into substantial beds, and the occasional occurrence of nearly pure quartzose or micaceous sand, sometimes quite free from carbonaceous admixture, either in the thinnest films or in thicker beds, will all then be naturally accounted for by one process, namely, the gradual deposition of laminæ and strata of different kinds of substances, with different degrees of mingling at the bottom of some water.
3rd. The phenomenon of the Flying reed.—If the reader will turn to page 39. Fig. 4, he will see that to account for the structure there described, on the principle of all coal-beds being of terrestrial growth, the following suppositions are necessary:— Firstly, the water was filled up to its surface, and on that level plain the Heathen coal was formed, then a depression took place, and a subsequent refilling of the water with earthy deposits, and then the Thick coal was formed. When, however, the accumoulation of the vast quantity of vegetable matter necessary for the production of the Thick coal was nearly completed, a very partial and local subsidence took place in one or two localities, bending down the previously formed beds into a hollow or pool of water, sufficiently deep for 128 feet of shale and sandstone to be accumulated, and thus another level floor formed for the growth of the upper bed of coal, which grew partly on the shale and sandstone, and partly on the undepressed coal. Then another depression took place, which was itself very unequal, and had this peculiarity, that over the part previously depressed it only amounted to 38 feet, while over the part not so depressed, and over the district generally, it was from 120 to 180 feet.[1]
4th. The expansion of the Thick and other coals towards the north.—When, however, we extend our observation beyond the
- ↑ It seems necessary to suppose that the depressions were unequal, and the irregularities levelled up to the surface of the water, by the accumulation of materials, because, if the depressions were equal over large spaces, and ¢he accumulations of unequal thickness, we should be obliged to call in the aid of unequal elevations or depressions again, to form a level surface "à fleur d'eau," for the growth of the next bed of coal.
