Geologic time rock dating
The basis for assuming that like fossils indicate contemporary formation is faunal succession.
However, as previously noted, times of volcanism and metamorphism, which are both critical parts of global processes, cannot be correlated by fossil content.
Using fossils simply for identification purposes, Smith constructed a map of the various surface rocks outcropping throughout England, Wales, and southern Scotland.
The first step is determining whether similar beds in separated outcrops can actually be traced laterally until they are seen to be part of the same original layer.With the development of miniaturized analytical equipment, evaluation of rock properties down a small drill hole has become possible.The technique, called well logging, involves lowering a small instrument down a drill hole on the end of a wire and making measurements continuously as the wire is played out in measured lengths.The more ways in which two rocks are physically alike, the more likely it is that the two formed at the same time.Only a partial listing of physical characteristics is necessary to indicate the breadth of approach in this area.
Ideally, an index fossil should be such as to guarantee that its presence in two separated rocks indicates their synchroneity.