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80 THE CIVIL ENGINEER AND these are found the stone of which we avail ourselves for con structive purposes. I have great reliance on what our friend Pro fessor Ansted says, because a gentleman of his experience must be aware, more than an architect, what is the real truth of the case as far as he has been able to investigate it. Granite is a most remarkable basis of rocks, and I should have been glad if our friend had described more ef the elementary parts of granite. There are an immense num her of ranges of mountains which consist of quartz entirely, and this we find to be the case in some of the Scotch mountains. If you go into Wales you find it in less quantity, though blocks of quartz are used in ornamental parts of cottages, and put into the walls of the buildings of the poorer as well as the superior classes. Now, the granite of Devonshire is peculiar, because occasionally we find it is imperfectly formed, the felspar of which it is largely composed, being so subject to disintegration, that we cannot rely upon it without due care. And yet there are parts where Cornish granite can be relied on just as much as Scotch. Wo find that London Bridge is built half of Cornish granite and half of Scotch, and the one has proved just as en during as the other. This mass of granite assumed formerly to be the basis of all rocks, was supposed to be penetrated by veins or fissures traversing the whole body of the mass of the rocks, and that through these cross-joints, veins, and fissures, there were certain igneous rocks of the serpentine and others thrown up, and spread themselves on the surface, and formed those rocks which we now use for the ornamental parts of architecture. These were not substances of deposit, nor really of infusion by wet; but by the heat thrown up and filling up these fissures and crevices which occurred in the primitive rocks, and which caused these fissures by the heat when the expansion took place and the cooling of the rocks left these fissures (I do not now speak of the vol canic series). These porphyritic marbles are found cither perfect or imperfect, and there are instances of porphyry, being so bad that in a few years it disintegrates. I had in my own practice a house to recase, because after thirty years the porphyry facing, so imperfectly formed, had disintegrated. I should have attributed this to the heat in the boiling not having been sufficient: but probably our friend will say, the water did not crystallize it enough. But at all events it was so imperfect that we were obliged to take it down and replace it with stone. With respect to the oolite, I do not believe there is on the face of the earth any stone, except the travertine we find in Rome, really better than our own Portland. In support of this I may refer to St. Paul’s Cathedral. It has been built above one hundred and fifty years, and if you look at the sculpture there the arrises are as perfect as possible; but Sir Christopher Wren took great precautions in the selection. He had persons on the spot to make choice of the beds and to watch that every block that was sent up was of the best quality. As I have already mentioned, I had to refaco this house in Devonshire, and I took Mr. C. H. Smith with me to select the stone, and we found still lying on the surface the very stones which had been rejected by Sir Christopher Wren’s agents as not sufficiently good for St. Paul’s. The blocks retained the tool-marks that were upon them at the time, and though they had been exposed to the atmosphere for above one hun dred and fifty years, the arrises were as sharp and as perfect as when they came out of the quarry. I bought a thousand pounds worth of that stone, and the masons found great difficulty in working it after having been weathered and exposed for so many years. This shows that if Portland stone be well chosen, from the proper beds, we may thoroughly rely on it. With respect to preservative applications to stone, I can hardly conceive that such simple substances as alum and soap can last for more than a very few years. I think you had much better paint the stone. In using stone you do not want a material that will last for five or ten years only, but that will last almost for eternity. Of all the various preservative processes we have heard of, that known as Ransome’s appears to give a guarantee of certain dura bility from the nature of the materials of which it is composed, viz.— silica. I come now to those rocks which are known as the schists. In Wales it is extraordinary to see in the quarries a wall of quartz of several feet in thickness, cutting through a whole mountain and inter secting the mass of slate. I should very much like our friend to ex plain this phenomenon. It is a most remarkable circumstance, because how has the slate been formed on one side or other of that mass of quartz which we see ? This wall is vertical. There must have been upheaving of that mountain. But was it first slate deposit, then the quartz, and then the slate deposit again upon that ? The upheaving would make it vertical by the interior heat of the earth. Or was it one of those veins, occurring from the action of heat in the earth, dividing the rock of slate, and filling it up with this quartz in solution ? That is another curious subject, and I hope my friend will pardon me if I allude to those matters which suggest themselves on the perusal of his interesting paper. I feel we ought not merely to take the surface of geology. It is of so much importance that the architect should dive deep into it, and possess all its leading principles. We may therefore congratulate ourselves in having such a paper as this from our friend, because he has cleared geology from much of those extraneous subjects which professional geologists are apt to attach to it. In dealing with it for our practical purposes, he has not treated of the various forms of different epochs, the organic remains of which are found in the rocks, ARCHITECT’S JOURNAL. ^ 1, 1868. but he has taken the obvious features which appear on the face of the rocks themselves. There are however other matters, such as how the rocks are superposed, which are ably treated in this paper. With re spect to the question of oolite-stone, that is a material of great interest to us. Alabaster is here and there treated of in rather opposite quali ties, a sulphate of lime being the component parts in some cases, and in other parts treated somewhat differently. It is a material used by us for ornamental purposes, and we have seen it much used by the Italians and French for similar decorative pm poses. But we know that alabaster was very largely used by the ancient Egyptians; and I have seen in the Tombs of Ghizeh a gallery completely lined with large slabs of this material. In the great mosque in the citadel of Cairo, built by Mohamet Ali, the whole of the interior is lined with alabaster, but it has been used with such want of taste that the general effect of this material, rich in itself, is poor and insipid. It wants some relief of dark marble or stone to give it emphasis and expression. It will be in the recollection of many that the late Pasha of Egypt sent to the Pope some shafts of alabaster, each composed of a single block, 30 feet in height and about 4 feet in diameter, to be used in the erec tion of the Basilica of St. Paul’s at Rome. I now come to the lime stone rocks, the origin of which is very interesting. The limestone rocks form a very large portion of the whole of the surface of the earth, and there is so much analogy in their composition with that of the bones of animals, that it has been stated by some, that these limestone rocks merely consisted of lime, the product of the bones of the animals which lived upon the earth at a certain time. This seems a startling proposition, but whether there is any other mode of accounting for the lime is a matter for curious enquiry. Whence the origin of the lime ? It cannot, I think, have been previously existing to what we used to call the igneous rocks, that is the granite, for we do not find any of this lime in the granite. How is it the lime comes to be alone, so as we find it upon the crust of the earth in the primary (or Pateogon) strata. I have no doubt our friend will be able to solve the difficulty suggested. Some are close-grained and compact limestones and they may be polished in the same manner as marble. In one of the churches at Paris (Notre Dame de Lorcte) the church is like an old basilica, and has columns along the central nave, a double row on each side. These columns were not intended to be polished, but the effect was so dull that they were obliged to bo so treated, and it proved a very costly remedy, almost as costly as if marble had been originally employed. With respect to porphyry it is difficult to polish that, because it is a very rotten material. Looking at the surface we find it is full of seams, and a great deal of clay apparently fills up the crevices and cracks. You cannot polish the clay, and therefore it is difficult to get an uni form mass of porphyry or of green marble. It is almost impossible to find a large block of homogenous green marble or porphyry, on account of the great quantity of clay that enters into the composition of it. With respect to slate we are all aware of the different qualities, and it is within about the last one hundred years only that it has been in troduced into general use in London for roofs. In ancient time it was the Westmoreland green slate which was used, which combined well with the decorative parts of a building in point of colour, and was very harmonious, But after a number of years the green slate becomes rotten like a piece of blotting paper, and therefore cannot be so well relied on as the blue slate of the Welch quarries. The former rotted where the lower end of the outer slate laps upon the one beneath. I am also anxious that our friend, if he will pardon me giving him so much trouble, will be good enough to explain more at large than he has done in his paper, the composition of marble. It has been con sidered that marble generally is a magnesian limestone. Whether it is pure lime crystallized I am not able to say, and I am also at a loss to account for some of the peculiar properties which belong to it. We know how beautiful it comes out in the working. The principal temples of Rome were built of marble, and that material being used for constructive as well as decorative purposes, great expense was of course involved. Mr. Nash mentioned how necessary it is for the young members of our profession to study the quarries. For my own part, I may say I never used a stone but I went to the quarry to see it there, and I invariably took a section of the quarry. It is of the greatest benefit to professional men to make themselves acquainted not merely with one or two, but as many quarries as they can take sections of, so as to understand the qualities of the beds. They almost always follow in the same series—the softer stones at the top and the harder stones at the bottom, down to the blue clay—there being no beds of any stone of greater depth than two feet; there may be two consecu tive strata of two feet each, but never one that is four feet deep without an intervening bed. Mr. William White.—The question has been raised with reference to the durability of slate, and I think that is one of the points in which we are more concerned than any other. There is a slate which has just now been brought into notice, and I was anxious to hear whether anything was known amongst those present as to its qualities in re spect of durability. The slate to which I refer, was introduced by Messrs. Randell and Saunders. It is a Cornish slate, but of green colour. It does not cleave into very fine laminin. From that, I con clude it would be liable to decay in due time, because I believe the