what did he conclude from studying volcanoes?
His conclusions supported gradual building of volcanoes, so-called "backed up-building", as opposed to the upheaval argument supported by other geologists.
Charles Lyell
One of the contributions that Lyell made in "Principles" was to explain the cause of earthquakes. Lyell, in contrast focused on recent earthquakes (150 yrs), evidenced by surface irregularities such as faults, fissures, stratigraphic displacements and depressions.

Lyell's work on volcanoes focused largely on Vesuvius and Etna, both of which he had earlier studied. His conclusions supported gradual building of volcanoes, so-called "backed up-building", as opposed to the upheaval argument supported by other geologists.
how do some chemicals in plants protect them from their enemies Through allelochemicals  that influence the behavior, growth, or survival of herbivores. name some animals/species that fall under the last-mentioned category. White-tailed deer , elephants, zebras, and giraffes. how would this category be defined? A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. where does the term come from? Herbivore is the anglicized form of a modern Latin coinage, "herbivora," cited in Charles Lyell's 1830 "Principles of Geology." who is this person mentioned here? Sir Charles Lyell, 1st Baronet, was a Scottish geologist who demonstrated the power of known natural causes in explaining Earth's history. what are some of his most renowned books? "Principles of Geology" .
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Charles Lyell [SEP] Volcanoes and geological dynamics
Before the work of Lyell, phenomena such as earthquakes were understood by the destruction that they brought. One of the contributions that Lyell made in "Principles" was to explain the cause of earthquakes. Lyell, in contrast focused on recent earthquakes (150 yrs), evidenced by surface irregularities such as faults, fissures, stratigraphic displacements and depressions. Lyell's work on volcanoes focused largely on Vesuvius and Etna, both of which he had earlier studied. His conclusions supported gradual building of volcanoes, so-called "backed up-building", as opposed to the upheaval argument supported by other geologists.