372 REPORT ON NATIONAL MUSEUM, 1886. 



calities. The flue-grained white varieties which appear like loaf sugar 

 are called saccharoidal. Common statuary marble is a good example of 

 this variety. 



Compact common limestone. — A fine-grained crystalline aggregate 

 which to the eye often appears quite homogeneous and amorphous. 

 It is rarely pure, but contains admixtures of other minerals, giving 

 rise to many varieties, to which particular names are given. Litho- 

 graphic limestone is an extremely fine-grained crystalline rock, with but 

 a small amount of impurities, and of a drab or yellowish hue. Bitu- 

 minous limestone contains a considerable proportion of bitumen, caused 

 by decomposing animal or vegetable matter. Its presence is easily 

 recognized by the odor of petroleun* given off when the rock is freshly 

 broken. Hydraulic limestone contains 10 per cent, and upwards of silica 

 and usually some alumina. When burnt into lime and made into mortar 

 or cement it has the property of setting under water. Oolitic limestones 

 are made up of small rounded concretionary grains that have become 

 cemented together to form a solid rock. These little rounded grains 

 resemble the roe of a fish ; hence the name, from the Greek word ooon, 

 an egg. Where the grains are nearly the size of a pea the rock is 

 called pisolite. Such a rock is now in process of formation along the 

 shore of Pyramid Lake, Nevada. Oolitic limestones suitable for build' 

 ing purposes are quite abundant in Iowa, Indiana, and Kentucky. 



Travertine, or Cole Sinter, is limestone deposited by running streams 

 and springs. It occurs in all gradations of texture from light flaky to 

 a compact rock fit for building. A light, porous calc sinter has been 

 deposited by the Mammoth Hot Springs of Yellowstone National Park, 

 some of which is nearly pure carbonate of lime and snowy white in 

 color. Travertine occurs in great abundance at Tivoli, in Italy, from 

 whence it was quarried in building ancient Eome. The exterior 

 of the Ampliitheatrum Flavium, or Colosseum, the largest theater the 

 world has ever known, was of this stone, as was also the more modern 

 structure of St. Peter's, in the same city.* The Latin name of the stone 

 was lapis Tiburtinus, of which the word "travertine" is supposed to be 

 a corruption. 



So far as is known the beds of this country are of limited extent and, 

 with one or two exceptions, unfit for any kind of structural purpose. 

 The pearly white and red " onyx" marble from San Luis Obispo and 

 Suisun City, Cal., are properly travertine; so are also the celebrated 

 "Mexican onyx" and so-called "Oriental alabaster" from Egypt. 



Stalactite and stalagmite are the names given to the deposits of lime- 

 stone on the roofs and floors of caves. Such are often beautifully crys- 

 talline and colored by metallic oxides, giving rise to beautiful marbles, 

 which are incorrectly called onyx, as are also the travertines, from which 

 they differ only in method of deposition. 



* Hull, Building and Ornamental Stones, pp. 279, 281. 



