Relative Dating Methods

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First, relative dating methods involve placing geological events in a sequential order as determined from their position in the rock record. Relative dating will not tell us how long ago a particular event occurred; only that one event preceded the other. Four principles of relative dating are of importance for this question:

1. Principle of superposition: Nicolas Steno realized that correct relative ages of horizontal (undeformed) strata could be determined by their position in a sequence of rock.

2. Principle of cross-cutting Relationship: holds that an igneous intrusion or a fault must be younger than the rocks it intrudes or displaces. This principle is very important in relative dating of geologic events and interpreting Earth history.

3. Principle of lateral continuity states that sediment extends laterally in all directions until it thins and pinches out or terminates against the edge of the depositional basin.

4. Principal of original horizontality: Steno reasoned that sediment is deposited in essentially horizontal layers

B. The (classifications and descriptions of the) four rocks are as follows:

· Shale-Mudstone is a detrital sedimentary rock (Any rocks exposed at the Earth's surface are subjected to mechanical and chemical weathering processes that disintegrate and decompose them, thereby yielding the raw materials for sedimentary rocks. All sediment is derived from preexisting rocks ands can be characterized as (1) detrital sediment, which consists of mineral grains and rock fragments, and (2) chemical sediment, consisting of minerals precipitated from solution by inorganic chemical processes or extracted from solution by organisms. In any case, sediment is deposited as an aggregate of loose solids such as sand on a beach or gravel in a stream channel.

· Limestone is a chemical sedimentary rock (Note: Refer to above note on sedimentary rock).

· Slate is a low-grade ...