See my comment on the parent for a study I did on these questions regarding reading strategies. Of particular relevance, Darwin kept detailed records of the books he read and wished to read in two notebooks [CUL-DAR119, CUL-DAR118], which spanned from his return aboard the Beagle until a few months after The Origin of Species was published.
http://darwin-online.org.uk/EditorialIntroductions/vanWyhe_n...