KINDS OF ROCKS. 431 



New York, of the Trenton period in geology, g. Conglomerate lime- 

 stones. 



The black marble of the United States comes mostly from Shore- 

 ham, Vermont, and other places in that State, near Lake Champlain, 

 and from near Plattsburg and Glenn's Falls, N. Y.; also from Isle 

 La Motte. A pudding-stone marble, of various dull shades of color, 

 occurs on the banks of the Potomac, in Maryland, 50 or 60 miles above 

 Washington ; it is used for columns in the interior of the Capitol at 

 Washington. 



The Portor is a Genoese marble very highly esteemed ; it is deep 

 black, with veinings of yellow ; the most beautiful comes from Porto- 

 Venese. The Nero-antico marble of the Italians is an ancient deep 

 black marble ; the paragone is a modern one, of a fine black color, 

 from Bergamo ; and panno di rnorte is another black marble with a 

 few white fossil shells. 



A beautiful marble from Sienna, brocatello di Siena, has a yellow 

 color, with large irregular spots and veins of bluish-red or purplish. 

 The maadelato of the Italians is a light red marble, with yellowish- 

 white spots. The Madreporic marble is the Pietra stellaria of the 

 Italians. 



Fire-marble, or lumachelle, is a dark brown shell marble, having 

 brilliant fire-like or chatoyant reflections from within. 



Ruin marble is a yellowish marble, with brownish shadings or lines 

 arranged so as to represent castles, towers, or cities in ruins. These 

 markings proceed from infiltrated iron. It is an indurated calcareous 

 marl, and does not occur in large slabs. 



Hydraulic limestone is a compact kind containing some clay, and 

 affording a quicklime the cement from which will set under water. 

 An analysis of a kind from Rondout, N. Y , afforded Carbonic acid 

 34*20, lime 25*50, magnesia 13*35, silica 15*37, alumina 9*13, iron 

 sesquioxide 2*25. In making ordinary mortar, quartz sand is mixed 

 with pure quicklime and water, and the chemical combination is 

 mainly that between the water and lime, together with subsequently 

 an absorption of carbonic acid. With " hydraulic cement," silica and 

 alumina (that of the clay) are disseminated through the lime, and 

 hence these ingredients enter into chemical union with the lime and 

 water, and make a much firmer cement, and one which " sets " under 

 water. 



Oil-bearing limestones occasionally occur. A kind used for build- 

 ing in Chicago, of the Niagara period, becomes spotted or streaked 

 with blackish mineral oil, after a few years' exposure to the weather. 



Some of the pyramids of Egypt, including the largest, the pyra- 

 mid of Cheops, is made of nummulitic limestone ; and this is the 

 building material of Aleppo, the range of mountains between Aleppo 

 and Antioch being composed largely of this cream -colored rock. 



A soft Tertiary limestone occurring in the vicinity of Paris has 

 afforded a vast amount of rock, of an agreeable pale yellowish color, 

 for fine buildings in Paris ; and a similar rock has long been usrd in 

 Marseilles, Montpellier, Bordeaux, Brussels, and other places in West- 

 ern Europe. 



Most limestones have been made out of comminuted shells, corals, 

 and other like material ; and when of dark colors or black, it is usu- 

 ally owing to some carbonaceous matters present derived from the de- 



