Geologists still use Steno's principles, with some refinements and additions.
Stratigraphy started to become a formal science due to the work of a man who published under the name Nicolaus Steno in the 17th century.
The most obvious feature of sedimentary rock is its layering.
This feature is produced by changes in deposition over time.
This means that a quartz sandstone deposited 500 million years ago will look very similar to a quartz sandstone deposited 50 years ago.
Making this processes even more difficult is the fact that due to plate tectonics some rock layers have been uplifted into mountains and eroded while others have subsided to form basins and be buried by younger sediments.