vi PREFACE TO THE FIRST EDITION. 



really scientific general knowledge of geology. Lyell's Elements 

 comes nearest to supplying this want ; but there are two objections to 

 this admirable work : 1. The principles (dynamical geology) are sepa- 

 rated from the elements (structural and historical geology), and treated 

 in a different work ; 2. Its treatment of American geology is of course 

 meager. 



I have treated several subjects in dynamical and structural geology 

 — e. g., rivers, glaciers, volcanoes, geysers, earthquakes, coral-reefs, 

 slaty cleavage, metamorphism, mineral veins, mountain-chains, etc. — 

 more fully than is common. I feel hopeful that many geologists and 

 physicists will thank me for so doing. I am confident that I give 

 somewhat fairly the present condition of science on these subjects. 



In the historical part I have found much more difficulty in being 

 scientific without being tiresome, and in being interesting without 

 being superficial and wordy. I have attempted to accomplish this diffi- 

 cult task by making evolution the central idea, about which many of 

 the facts are grouped. I have tried to keep this idea in view, as a 

 thread running through the whole history, often very slender — some- 

 times, indeed, invisible — but reappearing from time to time to give 

 consistency and meaning to the history. 



If this work have any advantage over others already before the 

 public, it is chiefly in the two points mentioned above, viz., in a fuller 

 presentation of some subjects in dynamical and structural geology, and 

 in the attempt to keep evolution in view, and to make it the central 

 idea of the history. Another advantage, I believe, is that it does not 

 seek to compete with the best works now before the public, but occu- 

 pies a distinct field and supplies a distinct want. 



I have confined myself mostly, though not entirely, to American 

 geology, especially in giving the distribution of the rocks and the 

 physical geography of the different periods. In only one case have I 

 made American geology subordinate, viz., in the Jura-Trias period, and 

 that only because of the meagerness of the record of this period in this 

 country. 



In a science so comprehensive and many-sided as geology, it is 

 simply impossible, as every teacher knows, to avoid anticipations in 

 one part of what strictly belongs to a subsequent part. It is for this 

 reason that the order of presentation of the different departments, and 

 of the various subjects under each department, is so different in the 



