Ann Ward, age 15, of Monroe, La., for her question:

WHERE DO WE GET TRAVERTINE?

Travertine is a buff colored or whitish limestone that is formed by the.deposits of calcium carbonate around springs and in streams. Deposits have been quarried in California, Colorado and other parts of the United States but the most famous bed of travertine forms the falls of the Anio River at Tivoli, near Rome in Italy.

The deposits near Rome are 500 feet thick in places. The travertine quarried there furnished much of the building stones for both ancient and modern Rome. The Colosseum and Saint Peter's Church were both built of it.

Travertine is porous and usually fairly soft when it is quarried, but it hardens later. Builders use it a great deal in mild climates.

In the United States, travertine is generally used only for finishing interior walls. Travertine is not used on outside walls where the temperature drops below freezing because it is pourous and retains much water. This water expands when it freezes and crumbles the rock.