Page:Popular Science Monthly Volume 52.djvu/55

Rh States Coast and Geodetic Survey; Prof. Charles D. Walcott (read by Prof. G. K. Gilbert), The Geographical Work of the United States Geological Survey.

The section of Geology was opened by the address of its president, Dr. G. M. Dawson, F. R. S., who gave an admirably clear and unbiased outline of the history and progress of Canadian geology, with special reference, of course, to the great labors and discoveries of Logan, Murray, Selwyn, and their co-workers in the Archæan and pre-Cambrian rocks of Canada. Professor Dawson well described and defined the Laurentian and Huronian terranes; but he does not favor the term Algonkian, and does not recognize it as expressing any definite system of rocks between the Huronian and the Cambrian. To go into any discussion of the many interesting papers in this section would be impossible within the limits of this, sketch. A large amount of attention was given to glacial geology, both by American and Canadian contributors—Professors Chamberlin, Fairchild, Gilbert, Hitchcock, and Willis among the former, and Professors Coleman, Spencer, Taylor, and Tyrrell among the latter. Mr. Tyrrell's account of the succession of the glaciers over Canada was of great interest, indicating three successive centers of ice-sheet movement over the region between the Rocky Mountains and Hudson Bay—the first western, the second central, and the third eastern. In the discussion that followed, some of the British members expressed great interest in this view, as corresponding with indications of a similar shifting of the glacial center of movement in Europe, but in the opposite direction—from the east westward. Prof. John Milne, who gave the evening lecture on Earthquakes and Volcanoes, laid before the section a report—the second made to the association—on Seismological Investigations, in which he developed some striking views. He regards the ocean floors as the great areas of instability and the seat of by far the chief part of seismic movements, and believes it probable that important faultings and sinkages are constantly occurring, and that such peculiar abyssal areas as the "Tuscarora deep," etc., and the frequent accidents to ocean cables, are evidences of this condition.

Passing over the sections devoted to biological subjects, zoölogy, botany, and physiology, in all of which the presidential addresses and the papers and discussions were of abundant interest, a few words must be given to those that dealt with other classes of facts—physical, chemical, and sociological. The address of Professor Ramsay on The Evidences for the Existence of a yet Undiscovered Gas coming between helium and argon in its density and its properties, and describing his elaborately delicate experiments to separate it, if possible, from helium—though as yet without definite