The annual stratification of pack ice has been examined. Summer layers are formed either by arrested growth or by thin layers of fresh-water ice. The crystal structure and the salt content of the ice reflect the seasonal cycle. During the growth of ice a pronounced orientation of crystalline structure develops; it is determined by vertical as well as by horizontal temperature gradients. There is a marked and systematic increase of salinity with depth, ranging from about 0.1 per mil at the surface to 4.0 per mil at a depth of 300 cm. This salinity distribution remains unaltered during the summer melt season. A tentative attempt has been made to reconstruct the growth history of the ice at Drifting Ice Station A. This shows that the winter growth is strongly related to the thickness of the ice, that the floe on which the station was located was probably eight years old, and that during each of the winters of 1955–1956, 1956–1957, and 1957–1958 the thickness ofthe ice increased nearly 60 cm.