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82 THE CIVIL ENGINEER AND ARCHITECT’S JOURNAL. [March 1, 1SCS. that the stone of that county might be largely imported into the south, and if you had Yorkshire masons to work it, it would not be more expensive than Portland stone. Care must however be taken not to use it for ashlar facing, which is generally about three or four inches thick, as you are almost sure to get it the wrong way of the bed, when it rapidly disintegrates if exposed to the weather ; but, if used in solid blocks and laid properly on the natural horizontal bed, it will last for centuries. Professor Kerr, Fellow, said—We are much indebted to Professor Ansted, because the subject of geology, as applied to architecture, is one which can never be other than full of interest. The real question, of course, is this—given our building stones, and given the evils and difficulties of durability incident to the nature of these stones,— can geology, which is so far the science of discovering the formation of these stones, be brought to bear upon those evils and difficulties so as to help us to understand and overcome them. Now, of course, the use of stone in architecture, or rather building, is simply this :—that mankind from the earliest ages have been accustomed, we shall say, to use this material in the enclosure of edifices, as against the weather. It does not however follow that there is any a priori reason why stone should be the material; but, we have never as yet discovered a better, and therefore accept it. Taking then this material as we at present find it, we may refer —first to sand-stone generally. Looking at it, not geologically, but practically, and by rule of thumb, we may regard sand-stone, of what ever kind, as being composed simply of sand cemented together in various ways by nature. A bed of such substance not cemented together we call sand ; and when Nature happens to have saturated this bed of sand with some cementing medium, it is sand-stone. Now suppose I say that I do not know why it is, that sand-stone of some of the most superior kinds has not been much introduced into London building; this is a practical question for geology to answer. In other words, looking at the uncertainty which prevails about the whole subject of London building stone, is it worth while to ask whether sand-stone is not in the nature of things the most promising material for London use? [Professor Donaldson. It is matter of cost]. I am not as yet speaking of the cost; there are certain buildings in which no cost has been spared, and yet the stone selected has not proved successful. Looking next at the lime-stones generally, we regard them as masses to concrete (chemical rather than mechanical) deposited from water, we shall say ; and when we find that these are selected for London use, whilst they are notably subject to certain disastrous effects of the London atmosphere, we ask geology to tell us, with regard to the formation of these stones (the question being another form of the previous one, if you please to call it so), whether they are really, as I think most of us have been accustomed to suppose, in their nature a superior material to sand-stones ; and further, if geology determines that they arc really the best material for town atmospheres, then we ask geology to say whether the facts of formation, theoretically, can be made to help us in respect of their practical employment, and perhaps their preservation. Then, looking in particular at the oolites, Professor Ansted tells us how they are formed; we have been accustomed to think they were formed in another way, but no doubt Professor Ansted is right, and the information is useful. We have been accustomed, I mean, per haps all of us, to regard oolitic lime-stone as composed of the debris of some pre-existing concrete lime-stone reduced by attrition to the form of egg-shaped sand, and then cemented together by a chemical deposit. We are told that is not so, that the oolitic character is pro duced by a tendency in the carbonate of lime, when in motion, to form those small granules round certain nuclei. I do not doubt that this is a good theory ; but I will call attention to a circumstance which may be interesting and suggestive, as bearing upon the question. A gentlemen, whom I am not authorised to name, but one who has taken part in discussions on stone at this Institute, has been making some experiments with, I believe (although this is his secret) whiting; and he has shown me a piece of what one would pronounce to be oolitic lime-stone, which he had produced by some means, perhaps by heat or electricity, out of this whiting, and I should think certainly not in any such way as to involve motion amongst tho particles, or their deposit around any nuclei. I cannot offer you any idea as to how this material had been produced; but I examined it with great interest as an artificial stone of the most distinctly oolitic character. Then looking next, still in our own way, and not geologically, at the magnesian lime-stones in particular, we are interested in asking of geology to explain what we as architects have never yet been able, as I think, to be made to understand (I do not think Professor Ansted has alluded to it), viz.—why it is, as matter of science, that the combination of the carbonates of magnesia and lime (the best being in nearly equal proportions) should produce that superior texture and character of stone which we know is produced. Let us look again at the dolomite formation; that is, crystalline magnesian lime-stone, the best of all stones, according to present opinion. I think we are told by geologists that it is produced by the passage through a formation of ordinary magnesian lime-stone of what may perhaps be called a current of volcanic heat, this being the reason of the crystalline character. It was on this theory that the stone of the Houses of Parliament was selected; but the result, nevertheless was in a measure unsatisfactory owing to the circumstance that, whilst the stone of a quarry may be more or less generally a dolomite, by reason of tho action of this incidental heat, there may be in the same quarry portions of the formation through which such heat has not passed, and which may prove to be, not merely a less perfect dolomite, but an inferior kind of stone, altogether non-crystalline, and yet at the same time undistinguishablo from the other by the eye. With regard to slate stones, I have nothing more to say than has been already said; but it occurred to me that there was in one respect a certain analogy between the formation of slate and the formation of CoigneVs betons agglomeres, and also of Austin and Seely’s artificial stone. I refer to the principle of using, for the mixing of the concrete which composes both these materials, the smallest possible quantity of water, and not employing a very heavy pressure, but rather a sort of constant punning. The result is a very hard and durable artificial stone of its kind. Whether slate is not produced upon some such similar principle, from a material which otherwise would be but dried clay, is a question. With regard to the durability of slate, I have heard to-night w hat was knew to me. It is a most important thing if we are to understand that slate will not last for even a reasonable numberof years. People who are inclined to that opinion ought certainly to enquire into the matter, and say definitely how long they believe it will last. If slate is solubla in water (this being the way to formulate the idea), the sooner we know that fact the better. There is one stone which has not been mentioned at all to night, and which, in my opinion, is one of the very best in England. I ought to have mentioned it with the dolomite ; it is the Mansfield sandstone. It is composed, like all sand-stones, first, of granules of indestructible quartz; but the cementing medium is no argillaceous, or simply calca reous, or nominally siliceous medium, but the magnesian limestone, crystalline, I suppose, of the neighbouring dolomite itself; so that it combines all the advantages of the mere sand-stone with the perfection at the same time, as I suppose, of the dolomite lime-stone. The question of durability with us architects (and I have been always speaking of durability alone, as the chief question for geological science) is, after all, reduced to two points, at any rate in London and other large towns,—namely, one which Professor Ansted will recognize as a practical point; and another which he may not be able to recognize so readily without some explanation. The first point is as to the simple durability or actual resistance to the weather, and the second as to what we call the “ colour” of these stones. The simple duration of stone has recently become reduced to the question of its duration in an unusually noxious atmosphere, such as, for instance, that which was selected for the seat of the legislature, a kind of air generated by the vapours of pottery works and bone manure mills in Lambeth, charged with the intermediate exhalations of the Thames. Certainly it must be good stone indeed which can withstand the action of such ungenial gases as these; and really it is a question of great importance for us to understand whether or not some of the sandstones—especially taking for example the magnesio-calciferous sandstone of Mansfield which I have spoken of—would not have been on the whole a bet ter material for London than any limestone whatever, or even mag nesian limestone. Then as regards colour there is this question—all the world knows it was on this score of colour that we went so far afield in the selection of stone for the Houses of Parliament. In respect of Portland stone we have portions of a building (say St. Paul’s) bleached to a cadaverous white, and other portions taking on the hue of a deep dirty black. Now, does any one know whether sandstone would or would not keep better colour in London than these ? In any case, if geology comes to our aid, if it could explain what the precise surface conditions are, which favour the putting on of this motley wear, the information would be very useful. With regard to the artificial preservation of stone, that is not a question raised in the paper, but I cannot help alluding to the extremely ingenious artificial stone of our friend Mr. Frederick Ransome. Any thing more ingenious in the way of an imitation of Nature has never, I think, been devised; and I am happy to hear Professor Ansted say, that in addition to other merits, he considers this ingenious material to be a good fire-stone. But, to keep to the point, 1 understand Professor Ansted to say, that Bath stone, if prepared on Mr. Ransome’s preservative principle (that is using silicate of soda with chloride of calcium), before being placed in the wall rather than after, would, in his opinion, be rendered highly durable. Might I ask whether he thinks the same process would answer in the case of the slates which we have been told are so liable to decay ? There is, lastly, one question of my own which I should like to be permitted to submit to the learned author of the paper before us. There was an idea, which appeared a very ingenious one, started some time ago by a Mr. Westmacott, namely, that lime mortar placed against natural limestone hardens rapidly by the abstraction of carbonic acid from the limestone. Chemists all declare that this is a delusion ; that the stone cannot part with any such carbonic acid. Nevertheless, Mr. Westmacott patented the principle, and he considers that if lime mortar be prepared with a certain proportion of bruised limestone or