To Geographers the origin of the varied distribution of the land and water, the cause and growth of mountains, plains, oceans, lakes and rivers, the great changes that have taken place on the face of the earth in times past, is of absorbing interest, rivaled only by their desire for perfect knowledge of that which may be seen to-day. Had the prehistoric man been gifted with the intelligence of his descendants in the present epoch, he would have left for us a record that would have been valuable indeed and cleared our way of much that now is speculation, and but too often food for words. True it is, however, that if the mysteries of the past were revealed to us we should lose the pleasures their study affords and perhaps there would follow a degeneration of species through the loss of stimulus they now provide. How long ago man lived and might have made a record is still a disputed question, but one that involves too, the record of the earth herself. The association of human remains in the Glacial drift brings that epoch in the earth's history nearer to us by several hundred thousand years, and instead of speculating upon it as having occurred nearly a million years ago, geologists must consider whether it was not probably coincident with the most recent eccentricity of the earth which astronomers teach us happened about ten or fifteen thousand years ago. Geology must also fit her facts to mathematical science if we give credence to latest computations. A mathematician has now advanced the theory that at the average depth of about five miles below the surface there is a belt of "no strain," the result of opposing forces above and below it, a belt that from the nature of the case is impenetrable, through which, what is above cannot pass to what is below, and what is below cannot pass to what is above, a condition that would confine the origin of all seismical and volcanic disturbances and their consequent Geographical changes, to a mere shell of the crust.1 The result of the computation is certainly interesting and we may hope will not be lost sight of in future discussions, however it may share in gaining support or opposition. It is based upon an assumption of the temperature when the earth began to cool, to assume a lower temperature draws the belt nearer to the surface and a higher temperature is believed to be inconsistent with our knowledge of what heat may effect. This belt is stated to be gradually sinking, however, and the computation, therefore, involves a term representing time, and I venture to suggest as estimates of Geologic time are generally indefinite and seem to be inexhaustible, an abundance can probably be supplied to sink the belt deep enough for all theoretical purposes.
1 In the American Geologist for February, 1888, Prof. Reade protests against the construction of the theory of a "belt or level of no strain" placing the foci of earthquakes and other disturbances in the strata above the belt.
More interesting to Geographers are the conceptions of ancient forms suggested by the views recently advanced by Prof. Shaler in a late number of Science (June 15, 1888), on "The Crenitic Hypothesis and Mountain Building." To let the imagination have full play, we may conceive that where we now have extensive mountain ranges, there were formerly great plains of sedimentation, and where we see the process of sedimentation active to-day there may be great mountains in the future. And also in his inquiry into the "Origin of the divisions between the layers of stratified rocks" (Proced. Boston Soc. Nat. Hist., vol. xxiii), we may be carried away with the immensity of the changes suggested. The recurring destruction of submarine life to contribute in the building of the rocks of the Continents: the apparently endless cycles of emergence of the land and subsidence of the waters, to leave the Geographical conditions we see to-day, furnish additional evidence of the wonders of the past and force upon us anew the realization of how little in the great evolution is the epoch in which we live.
American Geologists have advanced the knowledge of the world; only recently the American methods of Glacial study have enabled Salisbury to interpret the terminal moraines of Northern Germany (Am. Jour. Science, May, 1888), and that the Science is active among our countrymen is evidenced by the formation of a Geological Society and the establishment of a magazine devoted exclusively to its interests. America, too, contributed largely to the Geologic Congress recently held in London, and it is pleasing to note that the next session of the Congress is promised for Philadelphia.
At the suggestion of one of our associates I call the attention of the students of the science, and indeed all interested in it, and also of Geographers, to a recent publication entitled, "The Building of the British Isles," by Jukes-Browne (Scribner & Welford, N. Y.). It has been characterized as the best treatise on the evolution of the land areas which has yet appeared; from the Geologist point of view it is the book of the year. Another associate recommends to most attentive consideration the recent articles on "Three formations of the Middle Atlantic slope," by W. J. McGee (Am. Journal Science, Feb.–June, 1888), as one of the most original essays of recent years.
It also gives me great pleasure to bring to your attention an article on the "Physical Geography of New England," by Wm. M. Davis, in a book on the "Butterflies of New England," by S. H. Scudder. It is hardly necessary to recommend this publication to your perusal, as I doubt not being from the pens of our Associates, it will excite a lively interest in those devoted to these sciences.
In conclusion permit me to refer briefly to the "National Geographic Magazine," published by the Society, the first number of which has recently been placed before you. It is the desire of the Committee having charge of this publication to make it a journal of influence and usefulness. There is abundant material in the Society to furnish the substance, if those who have it at command will make legitimate use of their opportunities. It would be unfortunate if the text should be confined to the papers presented to the Society. It was not the intention of the Board of Managers that such should be the case, when the publication was determined upon. On the contrary, it was the expectation that there would be original communications from many sources: essays, reviews and notes on the various subjects of the five Departments in which the Society is organized, not necessarily from the members, but also from their friends interested in these divisions of the general subject. While this expectation has been realized in a measure, there is room for improvement and it is hoped the future will show an increasing interest and more generous contributions.
December, 1888.