the cement and sand and gravel used to make concrete, iron ore for steel, bauxite used in making aluminum, brick and tile, cutstone used for facing large buildings, and even asphalt for the roads which make these buildings accessible. in fact, almost everywhere you look you can find examples of the commercial and industrial uses of sedimentary rocks. though considerably less dramatic than such phenomena as volcanoes or earthquakes, sedimentary rocks are ultimately very important to our modern civilization. not only can they be economically valuable resources, but in the composition and structure of sedimentary rocks lies the best record of earth's long and complex history. to a geologist, this great stack of rocks in the walls of the grand canyon contains a fascinating story of earth history. it's a unique record of changing conditions at the earth's surface through time and a storehouse of information about the mountains and the source rocks that provided the sediments themselves. once we understand the significance of these rocks and of the clues they contain, we can read the record of