The leadership of Kellogg, after that of Marbut, was marked by an initial period of consolidation during which a series of decisions were made that brought the Soil Survey much closer to the practical problems of agriculture. This involved the publication of the Soil Survey Manual in 1937 and an account of the Development and significance of the Great Soil Groups of the United States in 1936; which were subsequently combined in the Yearbook of Agriculture for 1938, Soils and Men in a form more suited to farmers and the general public, where there was a stronger chemical emphasis. In 1949 an evaluation of the whole system was made when consideration was given to the role played by interpretive classifications, as well as of the factors of soil formation. This exercise helped to identify weaknesses in the classification and amendments that were necessary. However, the fundamental conclusion was reached that an entirely new classification system was necessary.