Publication of "Geological Observations on South America"; being Part III. of the "Geology of the Voyage of the 'Beagle'".
1851:
Publication of a "Monograph of the Fossil Lepadidae" and of a "Monograph of the sub-class Cirripedia".
"I fear the study of the Cirripedia will ever remain 'wholly unapplied,' and yet I feel that such study is better than castle-building."
1854:
Publication of Monographs of the Balanidae and Verrucidae.
"I worked steadily on this subject for...eight years, and ultimately published two thick volumes, describing all the known living species, and two thin quartos on the extinct species... My work was of considerable use to me, when I had to discuss in the "Origin of Species" the principles of a natural classification. Nevertheless, I doubt whether the work was worth the consumption of so much time."
"From September 1854 I devoted my whole time to arranging my huge pile of notes, to observing, and to experimenting in relation to the transmutation of species."
1856:
"Early in 1856 Lyell advised me to write out my views pretty fully, and I began at once to do so on a scale three or four times as extensive as that which was afterwards followed in my 'Origin of Species'."