He is best remembered for his geological (including stratigraphic) and faunistic investigations of the Alps. He also conducted important research on his numerous travels worldwide — Syria and Lebanon (1885), the Pyrenees (1886), the Himalayas (1892), Svalbard (1893), the Urals and the Caucasus (1897), North America (1901), et al. In 1895, with Wilhelm Heinrich Waagen, he proposed the Anisian Stage (a division of the Middle Triassic) as a replacement for the Alpine Muschelkalk.