Similar stratigraphic units can be correlated to each other. Principle of CorrelationĪccording to the principle of correlation: correlation is the matching of rock strata of the relative same age. Such breaks or gaps in the record are called unconformities. Law of UnconformitiesĪccording to the law of unconformities: At any place of the geologic record, there is evidence of crustal upliftment followed by a long period of erosion. It was first proposed by the Danish geological pioneer Nicholas Steno (16381686). The principle is important to the analysis of folded and tilted strata. Everest shows once it was the bottom of an ocean floor in historic time. The principle of original horizontality states that layers of sediment are originally deposited horizontally under the action of gravity. Ancient geography is reconstructed through an interpretation of the sedimentary rocks and fossils of a certain age. In the lower parts of the Grand Canyon are the oldest sedimentary formations, with igneous and metamorphic rocks at the very bottom. Some tectonic event, which occurred after they were deposited, has tilted these up to the angle they are now at. Flat layers of sedimentary rocks that are no longer horizontal. This principle states that layers of sediment are originally deposited horizontally under the action of gravity. The diagram (left) shows a cross-section of the rocks exposed on the walls of the Grand Canyon, illustrating the principle of cross-cutting relationships, superposition, and original horizontality. sedimentary rock layers are deposited horizontally when they form. This is the distribution and relationship of ancient seas and landmasses. The Principle of Original Horizontality was proposed by the Danish geological pioneer Nicholas Steno (16381686). newer).Īccording to the principle of cross-cutting relationship: Any geologic feature which cuts across or penetrates another body of rock must be younger than the rock mass penetrated.Īccording to Walther’s law of facies correlation: the succession of facies and lateral variation of deposition may be taken place at the same time in a different environment. Order rock layers into a sequence of relative age ( i.e.Since these fossil assemblages are unique for particular periods of the past, they can be used to: river deposits forming today have a similar composition and character as their ancient counterparts glacial erosional and depositional features are basically the same today as in the past… etc Principle of Biological SuccessionĪccording to the principle of biological succession: Different kinds of plants and animals succeed one another in time because life has evolved continuously therefore only rocks formed during the same age can contain similar assemblages of fossils. geologic processes operating today also operated in the past. According to the principle of uniformitarianism “The present is the key to the past” i.e.
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