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THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



[July. 



rate learn one of the most important branches of the science, viz., physica' 

 geology.] Granite is the basis upon which tlie whole system of rocks seems 

 to be founded, and where it retires from tlie human obserration, it is still 

 supposed to bed under the otiier rocks. Granite has been originally a fused 

 mass, and crystallised from a state of fusion: it is composed of mica, felspar, 

 and quartz, and is of a granular or grainy structure, from which it derives 

 its name, and these particles do not seem to be united by any intermediate 

 substance. The proportions in which its integral parts unite is of every 

 variety, as also its colour, which may be grey, red, yellow, green, or even 

 brownish-black, which colours proceed from the mixture of schorl and liorn- 

 blende. Granite is found in mountain chains, and genei'ally presents rugged 

 surfaces ; sometimes, however, it is columnar or pillar-like, and in the 

 PjTenees it abounds in masses of piles on piles. It is to be found all over 

 Europe. In England, in the North, in Cornwall, Devon, and Wales ; in 

 Scotland, in Caithness and in Aberdeen ; and in Ireland, in the mountains of 

 Armagh and Wicklow. In Gemiany it forms the Brocken and the Ilartz, 

 and it is the grand material in Switzerland and tlie Savoy. It is admirably 

 adapted for all purposes of architecture, even for paving and for statuary. 

 From ijts capability of receiving a tine polish, it was much used by the 

 ancients, and most of the monolithic monuments of Egypt, or those formed 

 of a single stone are made of this material, some of enormous dimensions, 

 particularly one 'at Thebes, and another at Rome, 100 feet high. In the 

 church of the Casan, at St. Petersburgh, are fifty of these columns, each 

 thirty feet high. 



In the same city (St. Petersburgh) also is an enormous mass of granite, 

 used for the pedestal of the celebrated statue of Peter the Great. Granite is 

 exceedingly liable to decomposition, from its being a compound substance ; 

 and, therefore, liable to injury, from its particles coming in contact with any- 

 thing dissimilar to their particular habits. So strongly is this tendency to 

 decay sometimes, that I recollect in the case of some granite statues brought 

 from Egyjjt to the British Museum, and laid in the court-yard for a short 

 time during the winter, that they became so affected by frost, as literally, in 

 some cases, to split to pieces, and almost fall into powder. 



Syenite derives its name from Syene, a city of Egyjit, in the manner that 

 many other rocks do ; thus chalcedony, from Chalcedon, tripoli, from Tripoli, 

 in Asia Minor, and chalk, or creta, from the island of Crete. It is composed 

 of felspar, hornblende, quartz, and mica, and resembles granite, but is of purer 

 grain, and contains hornblende. It is found in Scotland, in Aberdeen, and 

 in the isle of Arran, and is valuable, because it does not suffer from moisture 

 or from the atmosphere. It was much used by the ancients, but not so much 

 by the moderns. Some of the finest specimens are in the castle of Heidelberg, 

 on the Rhine, supposed to have been brought from the ancient palace of 

 Charlemagne. 



Gneiss is composed of mica, quartz, and felspar. It cleaves and works 

 more easily than granite, but is liable to injury from the weather. 



Basalt is of columnar form, generally of four or five sides, and is found 

 abundantly in natural structures. Although of volcanic formation, it is re- 

 markable that It is rare at A'esuvius, while it is in plenty at Etna. The 

 Giants' Causeway, in Ireland, is one of the finest specimens, containing thirtv 

 thousand pillars of this material. R is little used by the moderns, because 

 itis the hardest and least practicable of the rocks. ' Winckelman, however, 

 observes that the choicest of the ancient statues are of this material, as if the 

 sculptors loved to effect their triumph on that which was insuperable to 

 other hands. 



Porphyry is so named from a Greek word explaining its purple colour. It 

 IS of great variety, and is a general name for rocks containing a mineral mix- 

 ture. It was used abundantly by (he ancients, and at Rome are manv 

 buildings decorated with pillars supposed to have been brought from Con- 

 stantinople, buch are those in tbe Palace of the Conservatori on the Capitol, 

 in the Giustiniam i alace, in the Basilica of the Lateran, and in the church of 

 Santa Blana JMaggiore. 



Serpentine is also neglected by the moderns, but was used by the ancients 

 for tombs, vases, and small objects. 



Lava, peperino and pumice, are confined in their uses to volcanic districts, 

 atHerculaneum and Pompeii, which are principally built of such material. 

 Some of the early Etruscan tombs are composed of a coarse tr.achite, which is 

 supposed by some to point out the existence of an early state of society dur- 

 ing the geological periods. Pumice is occasionally preferred, on account of 

 the lightness of its texture. 



Having thus gone through the primary, we will now proceed to the secon- 

 dary rocks, in which we find .slate. The quality of a good slate is, that it 

 should cleave easily^ (],,,t (j,g lamina should be stra'ight, and unmixed 

 •with foreign substances, and the more finely laminated it is, tlie larger plates 

 will be obtainej. sjatg f^^ ^^^f^ should be dense and not porous, and itis 

 best judged, like other stones, by the sharpness of the sound. Porous slates 

 are bad, because they swallow water. Sulphur is a dangerous ingredient, and 

 sometimes exists in particles so minute, as to be imperceplible. 'J'his mineral 

 when mixed with water, produces vitriolic acid, and so promotes decomposi- 

 tion. 'Jo detect its presence, heat the slate with wood embers, and if it exists 

 it will give forth a sulphureous smell. Oxide of iron mixed with slate has a 

 sympathy for ^{^ and water, and so increases the quantity of oxide or rust. 

 Calcareous matter is equally injurious, and'may be tested by observing whether 

 it puffs up when exposed to muriatic acid. Carbonaceous, or coaly matter may 

 be detected by burning. With regard to its colour, yellow or black spots in- 

 dicate the presence of oxide, and black that of carbonaceous matter. The 

 best work on the qualities of slates is that of Pr. Watson, Bishop of Llan- 



daff, called " Chemical Essays," which has a whole chapter devoted to the 

 subject. 



Limestones are of various qualities ; those are be.st which are highly crys- 

 talised, but they are little used in modern times, on account of the cost of 

 making. These marbles, however, afford tbe best materials for building. 

 Those less crystalised are most commonly used by architects. 



While upon this subject it may be well to mention the manner in which 

 stones are arranged by the continental architects. They divide them into two 

 classes bard and soft, pierre dure and jtierre tenjre. Pierre dure is applied to 

 those which can only be worked by water and the plane-edged saw ; and 

 pierre teiidre to those which can be worked by the peg-toothed saw. 

 Tbe qualities which are required in a stone by the French and German 

 architects are, that it should be of a fine grain, and compact. Few stones, 

 however, possess all the qualities required, and then it is that the architect 

 must use his judgment in selecting the best. Thinly laminated (or leafed) 

 limestone, like lears of leaves in a book, possesses different degrees of 

 strength, according to its position. If placed so | on edge, it has, of course, 



less resistance and strength than when placed thus . Dark stones are 



generally the strongest; those which suck up water are bad; but those with 

 brilliant points and hard are good. A very good criterion is the sound of the 

 stone when struck with a metal instrument, when a full sound is a proof of a 

 good stone. Those mixed with sulphur are generally hard and good, but 

 require care in tbe selection. Heavy stones asdenoting compactness of struc- 

 ture. Another serious question is the evil arising from an imperfect character 

 of stone, from inattention to which many of our finest buildings in London are 

 injured. The Marquis of Northampton was observing to me, that to such 

 an extent does this devastation prevail at Oxford, that the number of col- 

 leges obliged to be refaced is extraordinary. 



\\'e are not, however, the only sufferers, our younger brethren in America mak- 

 ing the same complaint. A friend of mine, writing to me, says, " Our Capitol, 

 one of the finest senate-bouses in the world, scarce twenty years old, is so com- 

 pletely spoiled, tliat we are obliged to keep it always fresh painted, to pre- 

 serve it even from the wet. This mischief doubtless arises from mistaken 

 motives of economy , so that the builder is tied down by his contract to purchase 

 an inferior stone. We should not however look to cheapness but to quality, 

 for that is always the cheapest which is the best." 



Resuming our examination, we find next to slate old red sandstone, so 

 oalled from its being coloured with iron and nearly approaching grauwacke. 

 There are few of these stones good for building. 



The Carbonate of Limestone is very hard, and from its weight is difficult of 

 transport. Its hardness arises from the manv grains of quartz in it, and 

 practical men say that it cuts the saw, instead of the saw cutting the stone. 

 Craigleith stone is of this class, and it conies from a quarry of that name, two 

 miles from Edinburgh, where a great part of the New Town is built of 

 it. Bramlev fall stone also belongs to this division, and it is used in the 

 Temiinus of the Birmingham Railway at Euston Square. 



Passing over the coal formations, we come to Magnesian Limestone, which 

 unites rare qualities, being crystalline and hard, like the Carboniferous Lime- 

 stone, and easy to be worked, like Oolite. From the magnesia in it, itis a 

 very unproductive soil, and is so injurious to vegetation, that the lichens and 

 other small plants which disfigure stone will not grow on it. There is some 

 of excellent quality in Robin Hood quarry, near Gloucester, and there is 

 reason to believe that this class of stone will come into more general use. 



The New Red Sandstone extends over tlie island from Exeter to York, 

 and has many quarries, but it is not very appropriate for building purposes, 

 although formerly much used. The old builders, however, itmust be remem- 

 bered, took the stone nearest to hand, the bad roads being a great impediment 

 to the removal of such a bulky material. Worcester and Chester Cathedrals 

 are built of this stone, and have worn so badly that even in the interior the 

 faces of the statues are undistinguishable. These defects arise from beinc 

 much impregnated with oxide of iron, and also with saline particles, which 

 it derives from its neiglibourhood to the Cheshire salt-beds. The church of 

 St. Andrew, at Livei7)Ool, is quite black, the moisture imbibed by the salt 

 catching tbe soot and dirt floating in the air. 



The oolite formations are the great source of building materials, and derive 

 their name from the Greek, 00$, an egg, their structure being that of small 

 eggs. The Germans call it bluntly roestone. Roach Portland-stone, it should 

 be observed, is liable to cracks and fissures; Bath-stone is soft, but not du- 

 rable : Whitby sandstone is a good specimen of oolite. 



The Wealden formation affords Purbeck stone, formerly much used, some 

 of the pavements in the old streets of London being made of it. The Purbeck 

 marble was much used for ornamenting cathedrals. The Wealden sandstone 

 is very crumbling, but was used in Knowle Castle, and the other castles in 

 Kent. 



Chalk firestone is composed of marl and green sand, and is much used fox 

 ovens. The cloisters of Westminster Abbey are built of it. Chalk limestone 

 is rarely used, and is not much to be seen, except in St. Alban's Abbey. The 

 tertiary formations are not productive in England, while in France they 

 supply abundant materials, and are extensively employed at Paris. 



The Lias formations I have passed over, but it is not durable on account of 

 its containing pyrites. It is, however, well adapted for cements, and blue 

 lias lime isnow much used. 



The French Government has decided on proposing to the Chamber of De- 

 puties, to undertake tlie railroad from the capital to the Belgian frontier. 



