IRON MANUFACTURE. 275 careless to derive proper advantage from it; for instance, iron ore is very commonly found combined with clay, but sometimes, instead of clay, it is contained in calcareous earth. In order to manufacture the iron properly, there should, when put into the furnace, be a certain proportion between the limestone and the ore; but, for want of attending to this, I have heard that the iron-masters sometimes add limestone to ore which already abounds with calcareous ingredients, when, to effect their purpose, they ought to make use of clay to give the mass its just proportion."1 "Why then, when some clever person has made a grand discovery, it still requires a great deal of knowledge in others before it can be generally useful." "That is true to a great extent. Much good is done by such discoveries, but the ignorant and careless will be apt to blunder in applying them to practice. Recollect this, Harry, and always bring your understanding to bear upon whatever you take in hand. What you do, let it be done upon principle, and consider whether it is the best way of effecting your purpose. I believe this habit of applying the faculties to the common affairs of life is the foundation of that superiority we ob 1 Nicholson, ib. p. 328. serve in some persons who excel in almost every thing they undertake, because they set about it judiciously. Such persons are happier than others, from the constant activity of their minds, for it is certain that employments, in themselves irksome or laborious, may be converted into sources of pleasure, when the thoughts are occupied by the means of pursuing them to most advantage." "I will recollect this the next time I have any thing unpleasant to do." "Do so, Harry: as a boy or as a man you would find your account in it; and so would the ironmasters, whose inattention led us into this discussion. 66 I have told you what is meant by coal-fields, and seams of coal: the combined, alternating strata of sand-stone, shale and coal, have also the general name of coal-measures. Shale is frequently found lying immediately upon the seams of coal, so that when the coal is dug out, the shale becomes the roof of a low, dark cave or gallery, which I understand is the appearance presented by a coal-mine. You may suppose a deep shaft or pit, something like a well, which forms the entrance, and passes downwards through the series of strata. Those of coal being dug out, APPEARANCE OF COAL-MINES. 277 form low galleries one above another, communicating with the shaft, which in the first place was the means of access to the coal, and afterwards the channel through which it was raised to the surface." "I believe I understand all this very well. I can imagine a coal-mine. But I should like to ask papa about those little particulars which nobody can describe who has not actually seen the real thing. I am glad you mentioned the shale forming the roof of those coal-galleries; it seems such a likely situation for it to receive the impression of fern, or any other plant that happened to be uppermost, when the mass of vegetables was buried ; and yet there is one part of the business quite unintelligible." "What is that, Harry?" “I can imagine the mosses and ferns of the ancient Earth, buried in the way you once described, undergoing the bituminous fermentation, and, after a long lapse of ages, changed into coal; but how could they be brought into layers one above another thirty-two beds of coal! This is incomprehensible." "I think not, if you go back to the first bed of moss growing on the sandy rock, and overwhelmed by an irruption of water, which deposited a layer of clay or sand, or perhaps successive layers of each, upon the buried vegetables." "I can, and do imagine that. It is not the difficulty it is the doubling, the folding over, the placing bed upon bed, that puzzles me.” "You double, and fold, and fall into perplexity, because you are in a hurry-which Nature is not. She takes time for her operations. Suppose now that our inundation at length retires, and leaves a plain of clay or sand, will that plain be always barren?" "Certainly not," replied Harry. "And when it is covered with vegetation, may it not again be overflowed? And might not the same process be repeated ten, twenty, thirty-two times? It is only to suppose a deep valley overflowed and converted into a lake, drained, and again overflowed. We have no means of ascertaining the exact manner in which these revolutions were accomplished; but there is no difficulty in supposing a thing which is not in its nature improbable, and agrees with the actual appearance of the coal-fields, so far as to afford a satisfactory explanation of their origin." 1 Macculloch, ib. p. 312.-Ure, p. 185. FORMATION OF COAL. 279 "If this was the case, mamma, I see that the often-repeated inundation and deposition would gradually add to the weight, and press harder and harder. That would be a very important help in the change of a fermenting mass of vegetables into a close, hard, stony substance like coal: and if it is true, the formation of coal-fields would, after all, be a very simple operation." 66 "No doubt it was, Harry; whether the theory I have just attempted to explain in a familiar way be correct or not. What we call the laws of nature appear to be principles, or causes of action, very simple in themselves, but capable of extensive application. Do you not remember, That very law which moulds a tear, "Some philosophers suppose, that during the state of the earth in which coal was deposited, there was a gradual, though probably unequal, subsidence of the land; and that the coaly deposits took place in estuaries, or friths, as well as in lakes." 2 1 Gravitation. 2 Macculloch, ii. p. 313-Conybeare, p. 344-347. |