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.
Correlation is, as mentioned earlier, the technique of piecing together the informational content of separated outcrops.
When information derived from two outcrops is integrated, the time interval they represent is probably greater than that of each alone.
Suppose there exist a number of fossil-bearing outcrops each composed of sedimentary layers that can be arranged in relative order, primarily based on superposition.
Suppose, too, that all the layers contain a good representation of the animal life existing at the time of deposition.
As was mentioned at the outset of this article, fossil assemblages.
Following Smith’s pioneering work, generations of geologists have confirmed that similar and even more extensive fossil sequences exist elsewhere.
To this day, fossils are useful as correlation tools to geologists specializing in stratigraphy.
Using fossils simply for identification purposes, Smith constructed a map of the various surface rocks outcropping throughout England, Wales, and southern Scotland.
Smith’s geologic map was extremely crude, but in its effect on Earth study it was a milestone.
In addition, its fossilized population should be sufficiently abundant for discovery to be highly probable.