In spite of this deductive approach to interpreting natural events and the possibility that they might be preserved and later observed as part of a rock outcropping, little or no attention was given to the history—namely, the sequence of events in their natural progression—that might be preserved in these same rocks.by showing in very simple fashion that the layered rocks of Tuscany exhibit sequential change—that they contain a record of past events.Did they record the same series of geologic events in the Earth’s past?
The relative ages of the rock strata deduced in this manner can be corroborated and at times refined by the examination of the fossil forms present.
While making use of Steno’s principle of superposition, Lehmann recognized the existence of three distinct rock assemblages: (1) a successionally lowest category, the Primary (Urgebirge), composed mainly of crystalline rocks, (2) an intermediate category, or the Secondary (Flötzgebirge), composed of layered or stratified rocks containing fossils, and (3) a final or successionally youngest sequence of alluvial and related unconsolidated sediments (Angeschwemmtgebirge) thought to represent the most recent record of the Earth’s history.
This threefold classification scheme was successfully applied with minor alterations to studies in other areas of Europe by three of Lehmann’s contemporaries.
and the ensuing widespread dissemination of Steno’s ideas, other natural scientists of the latter part of the 17th and early 18th centuries applied them to their own work.
The early English geologist , for example, produced in 1725 what may well have been the first modern geologic maps of rock strata.