55 o THE POPULAR SCIENCE MONTHLY. 



and valleys, rivers and plains, and all its surface features, can not be 

 other than singularly feeble and imperfect, unless we realize what has 

 been the origin of these features. The land has had a history, not less 

 than the human races that inhabit it. 



One can hardly consider attentively the future progress of geog- 

 raphy without being convinced that, in the wide development yet in 

 store for this branch of human inquiry, one of its main lines of ad- 

 vance must be in the direction of what may be termed geographical 

 evolution. The geographer will no longer be content to take conti- 

 nents and islands, mountain-chains and river valleys, table-lands and 

 plains, as initial or aboriginal outlines of the earth's surface. He will 

 insist on knowing what the geologist can tell him regarding the growth 

 of these outlines. He will try to trace out the gradual evolution of a 

 continent, and may even construct maps to show its successive stages 

 of development. At the same time he will seek for information re- 

 garding the history of the plants and animals of the region, and may 

 find much to reward his inquiry as to the early migrations of the fauna 

 and flora, including those even of man himself. Thus his pictures of 

 the living world of to-day, as they become more detailed and accurate, 

 will include more and more distinctly a background of bygone geo- 

 graphical conditions, out of which, by continuous sequence, the present 

 conditions will be shown to have arisen. 



I propose this evening to sketch in mere outline the aspects of one 

 side of this evolutional geography. I wish to examine, in the first 

 place, the evidence whereby we establish the fundamental fact that the 

 present surface of any country or continent is not that which it has 

 always worn, and the data by which we may trace backward the 

 origin of the land ; and, in the second place, to consider, by way of 

 illustration, some of the more salient features in the gradual growth 

 of the framework of Europe. 



The first of these two divisions of the subject deals with general 

 principles, and may be conveniently grouped into two parts : 1. The 

 Materials of the Land. 2. The Building of the Land. 



The Materials of the Land. Without attempting to enter 

 into detailed treatment of this branch of the subject, we may, for the 

 immediate purpose in view, content ourselves with the broad, useful 

 classification of the materials of the land into two great series, (a) 

 Fragmental and (b) Crystalline. 



(a.) Fragmental. A very cursory examination of rocks in almost 

 any part of the world suffices to show that by far the larger portion of 

 them consists of compacted fragmentary materials. Shales, sandstones, 

 and conglomerates in infinite variety of texture and color, are piled 

 above each other to form the foundation of plains and the structure of 

 mountains. Each of these rocks is composed of distinct particles, worn 

 by air, rain, frost, springs, rivers, glaciers, or the sea, from previously 

 existing rocks. They are thus derivative formations, and their source, 



