Gravels are considered to be one of the most popular materials for teaching agency of water, that is, erosion, transportation, and deposition. Based on the composition, shape and size of gravels in the fluvial deposits, we can estimate the geology of the source area. The Fukuyama Formation, that is distributed in and around Fukuyama, Hiroshima Prefecture, is characterized by fluvial gravels. The composition and size of gravels from the Fukuyama Formation and recent river deposits are studied. The gravels from the Fukuyama Formaion is mostly composed of rhyolite, but those from recent river deposits contains both rhyolite and clastic rocks at the almost same rate. The difference in the gravel composition shows the change of distribution of rocks in the source area during the geologic time. It will be a good teaching material for getting the general ideas of the time and the space to consider the meaning of the difference.