806 ' J. D. Dana on American Geological History. 



of Geology ; and I propose, instead of simply reviewing recent 

 geological papers, to restrict myself to some of the general con* 

 elusions that flow from the researches of American geologists, 

 and the bearing of the facts or conclusions on geological science. 

 I shall touch briefly on the several topics, as it is a subject that 

 would more easily be brought into the compass of six hours than 

 one. In drawing conclusions among conflicting opinions, or on 

 points where no opinion has been expressed, I shall endeavor to 

 treat the subject and the views of others in all fairness, and shall 

 be satisfied if those who differ from me shall acknowledge that 

 I have honestly sought the truth. 



In the first place, we should have a clear apprehension of the 

 intent or aim of Geological Science. It has been often said, that 

 Geology is a history, the records of which are written in the 

 rocks : and such is its highest department. But is this clearly 

 appreciated ? If so, why do we find text-books, even the one 

 highest in authority in the English language, written back end 

 foremost,- — like a History of England commencing with the reign 

 of Victoria. In history, the phases of every age are deeply 

 rooted in the preceding, and intimately dependent on the whole 

 past. There is a literal unfolding of events as time moves on, 

 and this is eminently true of Geology. 



Geology is not simply the science of rocks, for rocks are but 

 incidents in the earth's history, and may or may not have been 

 the same in distant places. It has its more exalted end,- — even 

 the study of the progress of life from its earliest dawn to the 

 appearance of man ; and instead of saying that fossils are of use 

 to determine rocks, we should rather say that the rocks are of 

 use for the display of the succession of fossils. Both statements 

 are correct ; but the latter is the fundamental truth in the science. 



From the progress of life, geological time derives its division 

 into Ages, as has been so beautifully exhibited by Agassiz. The 

 successive phases in the progress of life are the great steps in 

 the earth's history. What if in one country the rocks make a 

 consecutive series without any marked interruption between two 

 of these great ages, while there is a break or convenient starting- 

 point in another ; does this alter the actuality of the ages ? It is 

 only like a book without chapters in one case, and with arbitrary 

 sections in another. Again, what if the events characteristic of 

 an age — that is, in Geology, the races of plants or animals — 

 appear to some extent in the preceding and following ages, so 

 that they thus blend with one another ? It is but an illustration 

 of the principle just stated, that time is one. Ages have their 

 progressive development, flowing partly out of earlier time, and 

 casting their lights and shadows into the far future. We dis- 

 tinguish the ages by the culmination of their grand characteristics, 

 as we would mark a wave by its crest 



