Geologists recognize rocks of three distinctly different modes of origin—sedimentary, igneous, and metamorphic, and there are many variations of each type. The sedimentary rocks of the Monument are composed of clay, silt, sand, and gravel carried and deposited by moving water; silt and fine sand transported by wind; and some limestone, composed mainly of the mineral calcium carbonate, which was precipitated from water solutions in freshwater lakes. In areas not far to the northeast and southwest are many sedimentary rocks of marine origin, that is, materials that were deposited in the ocean or shallow inland seas, but in the Monument marine sedimentary rocks occur only in parts of the Dakota Sandstone; however, the overlying marine Mancos Shale underlies the adjacent Grand Valley and forms the lower slopes of the Book Cliffs across the valley (fig. 25). Igneous rocks were solidified from liquid molten rock intruded upward into any preexisting rocks along cracks, joints, and faults. Molten rock that reaches the land surface and forms volcanos or lava flows is called extrusive igneous rock. Joints are cracks or breaks in rocks along which no movement has taken place. Faults are cracks or joints along which one side has moved relative to the other. Different types of faults are shown in figure 28. Metamorphic rocks were formed from either of the other types by great heat and pressure at extreme depths in the Earth’s crust. Metamorphic rocks and some intrusive igneous rocks make up the hard, dark rock that floors all the deep canyons in and near the Monument. The nearest extrusive igneous rocks are the thick, dark lava flows that cap towering Grand Mesa to the east and Battlement Mesa to the northeast. [Illustration: INDEPENDENCE MONUMENT, separating the two entrances of Monument Canyon. Looking north from Grand View; Colorado River, Grand Valley, and Book Cliffs in distance. Roan Cliffs are white cliffs at extreme distance on right skyline. Dark rock flooring canyon is Proterozoic metamorphic rock, red material in slope at base of cliffs is the Chinle Formation, vertical cliffs are Wingate Sandstone, thin protective caprock on top of cliffs is lower sandstone of the resistant Kayenta Formation. The top of Independence Monument is nearly 450 feet above the floor of the canyon. (Fig. 6)] [Illustration: ROCK COLUMN OF COLORADO NATIONAL MONUMENT. 1 foot = 0.305 meter. (Fig. 7)]