A systematic attempt to apply hydrography to describe the waters of the ocean as developed by Wust and his students in the 1930s. In this method he distinguished between different core layers characterised by maxima or minima in their oxygen, salinity or temperature fields. While of unquestioned descriptive value, this method has some significant limitations. The number of layers that can be identified using this techique is limited, e.g. Wust identified just seven such layers in the North Atlantic, a shortcoming ameliorated by the development of the isopycnal method. Also, these layers were too often uncritically assumed to be the main paths of ocean circulation, an assumption that has been proven to be incorrect on more than one occasion.