Jean Louis Rodolphe Agassiz (1807-1873), Swiss-US naturalist. Louis Agassiz was born in Switzerland. He produced a catalogue of fossil fish from Brazil in 1829, and completed an extensive history of European fish in 1842. He wrote a pioneering five- volume work on fossil fish in 1843. He moved to the USA in 1846, and from his studies there he proposed the idea of Ice Ages: his research on glaciers led him to conclude that ice sheets advanced and retreated over Europe and North America. He was also a leading critic of Darwin's evolution theories. This photograph, by James Wallace Black (1825-1896), was produced around 1861, as a carte de visite portrait by J.E. Tilton and Company, Boston, USA.