Conglomerate forms in a very energetic environment, where rocks are eroded and carried downhill so swiftly that they aren't fully broken down into sand. Another name for conglomerate is puddingstone, especially if the large clasts are well rounded and the matrix around them is very fine sand or clay. A conglomerate with jagged, broken clasts is usually called a breccia.
Conglomerate is often much harder and resistant than the sandstones and shales that surround it. Conglomerate is scientifically valuable because the individual stones are samples of the older rocks that were exposed as it was forming—important clues about the ancient environment.
See more conglomerate examples, and other sedimentary rocks, in the Sedimentary Rocks Gallery.
Other galleries:
Fossils
Geologic Features and Processes
Glaciers and Ice
Landforms
Minerals
Rocks
Geology and Society