At the time when one of the upper strata was being formed, the lower stratum had already gained the consistency of a solid ... At the time when any stratum was being formed, all the matter resting upon it was fluid, and therefore, at the time when the lowest stratum was being formed, none of the upper strata existed.
In other words, Steno proposed that the layers of rock were laid down one layer at a time with the layers on the bottom being older than the layers on top. Steno performed no experimentation to test this claim, and as Berthault points out, when it was actually put to the test in the field by Johannes Walther in the late nineteenth century, it was discovered that Steno was very much mistaken. Berthault builds on Walther’s discovery by demonstrating that the results found in the field can be reproduced under controlled circumstances in a laboratory. Both the field studies of Johannes Walther and the laboratory experiments by Guy Berthault show that multiple layers of rock in Earth’s crust formed simultaneously as the result of natural particle sorting.