XIII. 



THE GEOGNOSY OF THE APPALACHI- 

 ANS AND THE ORIGIN OF CRYSTAL- 

 LINE ROCKS. 



The following address was delivered on retiring from the office of president of 

 the American Association for the Advancement of Science at Indianapolis, August 

 16, 1871. It appears in the Proceedings of the Association and in the American 

 Naturalist for October, and, with some abridgment of the first part, in Nature. A 

 French translation of the entire address was also published in the Revue Scieritifique. 

 In reprinting it a few sentences have been substituted for the original references 

 to the Cambrian rocks of Great Britian, and a fuller account of the Norian or 

 Labrador series has been introduced, besides some minor additions in the first 

 part. In the second part of the paper, also, important additions .have been made. 

 These new portions are distinguished by being enclosed in brackets. 



In the American Journal of Science for February, 1872, appeared an adverse criti- 

 cism of some parts of the address, by Professor J. D. Dana, to which the author in the 

 same Journal for July, 1872, made a reply, which is here printed as an appendix to the 

 paper ; the short portion relating to geognosy being at the close. Professor Dana's 

 rejoinder will be found in the same Journal for August, 1872. 



IN accordance with our custom it becomes my duty, in quit- 

 ting the honorable position of president, which I have filled 

 for the past year, to address you upon some theme which 

 shall be germane to the objects of the Association. The pre- 

 siding officer, as you are aware, is generally chosen to represent 

 alternately one of the two great sections into which the mem- 

 bers of the Association are supposed to be divided ; namely, 

 the students of the natural-history sciences on the one hand, 

 and of the physico-mathematical and chemical sciences on the 

 other. The arrangement by which, in our organization, geology 

 is classed with the natural-history division, is based upon what 

 may fairly be challenged as a somewhat narrow conception of 

 its scope and aims. While theoretical geology or geogeny 

 investigates the astronomical, physical, chemical, and biological 



