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Rock Layers. Compaction. Happens when pressure is applied to a material (over long periods of time). Cementation. Involves the deposition of a cementing matrix in the pore spaces between the grains of sediment. Before cementation (notice the air spaces). horizontal. Level- like a floor
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Compaction • Happens when pressure is applied to a material (over long periods of time)
Cementation • Involves the deposition of a cementing matrix in the pore spaces between the grains of sediment
horizontal • Level- like a floor • Not higher on one side or the other
Principle of Original Horizontality • Each new deposit of sediment forms a new horizontal layer on top of the layer below
PRINCIPLE OF ORIGINAL HORIZONTALITY • • Sedimentary and extrusive igneous rocks are originally laid down in horizontal layers • • any change from that is viewed as a disturbance of those layers (something happened later) • folding, tilting (occur during mountain-building events, for example) • sedimentary and igneous extrusive rocks that are folded or tilted must have first been deposited in horizontal layers before being folded or tilted. • 1. layer deposited • 2. layer deposited • 3. layer deposited • 4. all three layers are tilted Label the above (1-4)
Uniform • The way things happen today is the same way things have always happened
Uniformitarianism • Means that the present is the key to the past