Complex sentence: Williams kept a daily journal of his activities, which has since produced information concerning the lives of Shelley, Byron, Trelawny, and a pencil sketch from 1821 is the only good likeness of the poet.
Split into simpler sentences: Williams kept a daily journal of his activities, which has since produced information on the lives of Shelley, Byron and Trelawny. A pencil sketch from Williams's journal in 1821 is the only good likeness of the poet.