“Tremble, O earth, before the Lord, Before the God of Jacob, Who turned the rock into a pool of water, The flint into a fountain of water.” Ps 114:7-8 (NASB)
Rocks come in three basic types: sedimentary, metamorphic, and igneous. Igneous rocks are produced through volcanic activity. Metamorphic rocks are produced by intense pressure. Sedimentary rock is essentially made by concretion.
Sedimentary rock is formed when water reacts chemically to cement particles of sediment. The specific type of sedimentary rock depends mostly on the chemistry of the raw particles. Thick sheets of fossil rich limestone, sandstone and dolomite form the bedrock under the topsoil of much of North America. For the moment let us put aside the question of how old any given part of the sedimentary rock layers might be. Instead, we will first ask whether the layers of sedimentary rock we observe were laid down quickly or slowly.
The Uniformitarian model states that sediment is laid down slowly, layer on layer, over vast ages. If we allow for periodic local flooding in a given area over millions of years, we would expect to see the effects of erosion on the top surfaces of sedimentary rock layers. The boundaries between the layers should be relatively smooth. There should be evidence of weathering with wind and water wear.
The Genesis flood model predicts a sudden movement of sediment in violent water. The effects should be widespread across large areas. The sediment layers should be of varying depths and composition. Layers would not have an opportunity to dry and harden before additional layers would be deposited. This in turn means we would not expect to find mostly smooth boundaries between layers. We would expect to find rough surfaces, ripples, and “fossilization” of whatever surface features a layer may have had when later layers were dumped on top.
Smooth layer breaks are almost never found in nature. Instead ripple-like breaks are often found between sedimentary rock layers. Rapid burial is the only reasonable explanation for detailed surface features like ripples and droplets in sedimentary rock layer boundaries. Most sedimentary rocks have vivid surface features where layers of rock interface. This sort of interface suggests a rapid depositing of layers by a flood of rushing sediment pouring in and swirling as currents shifted, ebbed, and flowed. The rock boundary evidence in nature fits the Genesis flood model far better than the Uniformitarian model.
Another problem for the Uniformitarian theory is the lack of observable natural processes at work today producing natural sedimentary rock similar what we find when we dig just a few feet down in much of the continental United States.