Approximately 140 years ago William Smith discovered the use of fossils in correlation. Most of his life had been spent as a surveyor crossing and recrossing the Jurassic rocks of England where the structure is simple and many of the formations are easily identified by lithology. Distinctive beds can be traced along the outcrop from quarry to quarry where Smith was wont to hunt fossils, and thus he came to realize that each formation has distinctive species by which it can be identified without the trouble of tracing.
It is no accident that within the half century following Smith’s discovery the entire geologic column was securely established and all the systems were correctly identified, not merely in England but across the whole of Europe and eastern North America, for no other conception has ever become such an open sesame to the secrets of Earth’s history. Without it we should . . .