In 1866 and 1867 important papers appeared by Charles Whittlesey, and one by Edward Hungerford; this last, read before the association, adopted the general views of Agassiz, with some important limitations now generally received. In the same year the revised edition of Dana's Manual gave yet fuller statement and wider diffusion to the generally accepted views as held to-day. Professor Fairchild sums up this historical sketch as comprising four periods--viz., prior to 1841, undisputed reign of diluvial hypotheses; 1841 to 1848, suggestion and discussion of glacial hypotheses; 1849 to 1866, gradual acceptance of the latter view; from 1867 onward, development of glacial geology. From this point, the address was occupied with consideration of the various aspects of the subject as studied and wrought out during the past twenty years by numerous observers. These are grouped under four main heads, each with various subdivisions--viz., (1) the ice sheet, as to its area, its thickness, its centers of dispersion, its migration of centers, etc.; (2) the ice period, as to its cause, its divisions, its duration, its distance in time; (3) the interpretation of special phenomena, such as moraines, drumlins, eskers, "kettles," and the like, valley drift, terraces, loess, etc.; and (4) existing glaciers, as discovered on our high mountains of the far West, and as studied in closer relation to the ancient phenomena in the great ice cap of Greenland and the immense glacier development in Alaska. It is impossible to go into a detailed review of the numerous points of interest covered in this discussion. Suffice it to say that one who heard or who reads it finds an admirably clear and condensed account of all the problems and phenomena that have been and that are now encountered in the study of glacial geology on this continent, and of their gradual interpretation and solution by the combined labors of many students. The progress of knowledge over this wide field, advancing step by step, amid conflicting views and perplexing conditions, is beautifully shown, and leaves a very striking impression on the mind, of the difficulties and the successes of scientific research. Nor is Professor Fairchild disposed to claim too much or assert too strongly. He recognizes that, with all that has been met and mastered, there are still questions unsolved, and laurels to be won by others.