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Earth Geology Rock Types Sandstone


Sandstone is a rock composed of sand-sized grains of quartz (SiO2) that have been lithified or cemented together. Sandstone forms the most prominent layers of the Roubidoux Formation, which creates the characteristic bluffs along the Bryant and its tributaries. The sandstone-capped bluffs of the Roubidoux give the Bryant its distinctive character. Weathering of the sandstone produces the sand of the sand bars along the creek channels and the sandy soils of the rich bottomlands along the Bryant. 

The sandstone layers of the Roubidoux are good aquifers and springs are usually found where the Roubidoux is cut by stream valleys. The springs that powered the old grist mills and provide the cold waters for modern fish hatcheries are all in the Roubidoux. 

Color variations in a sandstone outcrop.
Cross bedding (angular layering)
between horizontally bedded sandstone layers.
Fossil ripple marks in sandstone stream bed.
Fossil mudcracks.

The sandstone layers typically weather to a medium-light gray outcrop. On freshly broken surfaces the sandstone varies from white through shades of tan and reddish brown. The red tints are due to iron oxide within the cement that holds the sand grains together (Figure 1). 

Textures within the sandstone layers such as cross-bedding, ripple marks, and mud cracks, are clues to the origin of the layers as shallow, intertidal or delta sediments (Figures 2 - 4).