420 ROCKS AND BUILDING STONES OF THE EARTH 



and modified by its new underground conditions. Not only 

 igneous rocks, but also sedimentary rocks are modified by con- 



FIG. 286. Quarrying for marble. (Courtesy of Philadelphia Commercial Museum.) 



ditions, and may lose their original composition. Igneous and 

 sedimentary rock which have been altered in character in any 

 way are known as metamorphic rock (Fig. 285). 



