Soru

Passage:
In 1799, English surveyor William Smith produced the first geological map based on the principle of faunal succession, which posits that sedimentary rock strata contain fossilized flora and fauna that succeed each other vertically in a specific, reliable order. While earlier naturalists recognized that rock layers differed in lithology—their physical composition and texture—Smith observed that physically identical strata at geographically separate locations could be distinguished by the unique assemblages of fossilized organisms embedded within them. Working as a canal surveyor, Smith noticed that specific fossil species consistently appeared in the same relative vertical sequence across distant quarry sites, even when the surrounding rock types varied. By systematically cataloging these index fossils, Smith established that layers containing identical fossil assemblages were deposited during the same geological timeframe, regardless of their mineral composition. Consequently, Smith was able to correlate disparate rock formations across Britain and construct a comprehensive stratigraphic map. Prior to Smith’s work, geologists relied exclusively on mineral characteristics to identify rock strata, a method that frequently produced errors when different strata composed of identical sandstone or limestone were misidentified as a single continuous formation.

According to the passage, William Smith was able to distinguish between rock strata of identical physical composition at different geographic sites primarily by doing which of the following?