“Principles of Geology”, written by Charles Lyell and published between 1830 and 1833, was of key importance for the development of Darwin’s theory. The book was released during the Voyage of the Beagle and Darwin read it as the trip progressed. It served as the basis for a theoretical framework of the scientist’s observations.
Lyell’s work marks a great change in the geologic theory. He proposed that the key to understand the presence of seashells in high and unexpected places was the constant, gradual and inconceivably slow movement of the changes that took place on Earth. There were no catastrophes, just geologic laws that could be observed in the present and that had worked incessantly through eons of time.