Here's what Darwin reasoned:
* Fossil shells at high altitude: Finding marine fossils high up in the mountains suggested that the land had been submerged in the ocean in the past. This contradicted the prevailing view of a young Earth with unchanging species.
* Gradual uplift: The presence of the fossils at such a height indicated that the land had been gradually uplifted over a long period, contradicting the then-popular idea of sudden, catastrophic events shaping the Earth.
* Change over time: Darwin observed that the fossils were different from the shells of modern marine creatures, implying that species change over time. This observation fueled his theory of evolution by natural selection.
This discovery, coupled with his other observations during his voyage on the Beagle, played a crucial role in Darwin's development of the theory of evolution.
