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 highlv 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 morte 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 mandelatv of the Italians is a light red marble, with yellowish- 
white spots. The Madreporic marble is the Pietru stclluiiw of the 
Italians. 
Fire-marble, or lumachelle, is a dark brown shell marble, having 
brilliant fire-like or chatovant 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 12°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 c mbination 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 tl.e 
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 uscd 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- 
clly owing to some carbonaceous matters present derived from the de- 
