Sources of geological information

The Earth is now estimated to be 4.6 bUlion years old. The different rock types formed at different times have assigned ages of their time of formation from the present time based on the geological time units of the geological time scale. Stratigraphy determines the succession in time of rocks to establish the sequence in which the rocks were deposited or formed. 

The duration of Earth history or geologic time is divided into intervals of time. This geological time scale with a hierarchy of time units is given in Table 2.1. An example of a time unit is the Cretaceous Period and one of its sub-divisions is the Campanian Age. 

The information most often required for engineering purposes is the lithological and structural information. These stratigraphic rock units or map units normally do not have different constituent rock types individually demarcated but these may be found mentioned collectivity in the legend. This tends to drastically limit their usefulness for engineering purposes. However, in spite of this limitation there is one map unit referred to as the Quaternary that does assist directly in engineering site investigations of sedimentary rocks. 

The fundamental lithostratigraphic rock unit is the Formation. A Formation is defined as a prevailingly body of rock identified by lithic characteristics that can be mapped in the field as a continuous unit. Formations can be, although they do not have to be, divided into members or grouped into groups as in Table 2.3. 

Formation A physically continuous unit of strata that have a consistent lithic character that differs from adjacent units 

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Thermal data were obtained from various sources of geological information the actual data of the mineral used as filler in the polymer industry might be slightly different. 

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