[100] The Arab Chain is almost entirely calcareous. Near the sites of all the ancient cities it shows numerous excavations bearing witness to the activity of the ancient builders. The most celebrated of these quarries is that at Mokattam, near Cairo. The stone of which the body of the pyramids is composed was drawn from it. [101] The alabaster quarries of to-day are all in the Arab Chain, between the southern slopes of the mountain Mahsarah, near Cairo, and the springs of the Wady-Siout, opposite the town of that name. Sandstone and limestone, especially the latter, are used nearly everywhere; granite is of less frequent occurrence and suggests an important observation. Granite is not a sedimentary, stratified rock like limestone; it is a material compacted in great masses, to a depth or, to speak more accurately, in a volume which is practically unlimited; the dimensions of the stones which may be cut from these masses are therefore infinite to all intents and purposes.[102] [102] The obelisk of Queen Hatasu, at Karnak, is 105 ft. 8 in. high; the statue of Rameses II. at Thebes, on the left bank of the river, is a monolith 55 ft. 5 in. high, and weighing about 1,200 tons. [The obelisk which still remains at Syene, never having been completely detached from the rock in which it was quarried, is nearly 96 ft. high and 11 ft. 1-1/2 in. diameter at its base.--ED.] The Egyptians also made use of both burnt and unburnt brick. The employment of these different materials gave birth to what we may call "dressed construction," that is, construction the elements of which are squared upon each face and put into close juxtaposition one with another. Concrete or pisé, compressed, as in the pylons, between moulds or caissons of woodwork, was also made use of by the Egyptians. This material gave rise to what we may call compact construction. Again, although trees, except the palm, were rare enough in the valley of the Nile, the Egyptians built also in wood, by which a third kind of construction, called construction by assemblage, in which the elementary units were held together by being introduced one into another, was obtained. In a few buildings of the latter class metal seems to have been employed, sometimes in the construction, sometimes for lining, and sometimes for outward decoration. §4.--_Dressed Construction._ The constructive elements which enter into the composition of this first class of buildings are stone and brick. In the first place, these elements are horizontal or vertical. The horizontal elements constitute the planes, as they cover the voids by horizontal superposition. They consist of courses and architraves.