摘要
schoot van der Gracht, who generously permitted him to use maps, charts, and manuscripts of important papers in advance of publica-tion, and to Drs. Chas. H. Behre, Wm. Bowie, A. F. Buddington, L. Brand, N. M. Fenneman, T. S. Lovering and W. P. Woodring for critical reading of certain chapters or parts of chapters. The writer isespecially indebted to two friends who read the whole manuscript, giving much valuable advice as to contents and form: Dr. TaylorThom and Mrs. L. S. Brand.