Nov. 2, 1871] 



NATURE 



15 



THE GEOGNOSY OF THE APPALACHIANS 

 AND THE ORIGIN OF CRYSTALLINE 

 ROCKS* 



IN coming before you this evening my first duty is to announce 

 the death of Trof. William Chauvenet. This sad event was 

 rot unexpected, since, at the time of his election to the presi- 

 dency of the Association, at the close of our meeting at Salem 

 in August 1869, it was already feared that failing health would 

 prevent him from meeting with us at Troy, in 1870. This, as 

 you are aware, was the case, and I was therefore called to pre- 

 side over the Association in his stead. In the autumn of 1869, 

 he was compelled by illness to resign his position of Chancellor 

 of the Washington Universily of St. Louis, and in Deceinber 

 last died at the age of fifty years, leaving behind him a record 

 to which Science and his country may point with just pride. 

 During his connection of fourteen years with the Naval Academy 

 at Annapolis he was the chief instrument in building up that 

 institution, \\hich he left in 1859 to take the chair of Astronomy 

 and Mathematics at St. Louis, where his remarkable qualities 

 led to his selection, in 1S62, for the post of Chancellor of the 

 University, which he filled with great credit and usefulness up to 

 the lime of his resignation. It is not for me to pronounce the 

 eulogy of Prof. Chauvenet, to speak of his profound attainments 

 in astronomy and mathematics, or of his published works, which 

 have already taKen rank as classics in the literature of these 

 sciences. Others more familiar with his field of labour may in 

 proper time and place attempt the task. All who knew him can 

 however join with me in testifying to his excellences as a man, 

 an instructor, and a friend. In his assiduous devo'ion to scien- 

 tific studies he did not neglect the more elegant arts, but was a 

 skilful musician, and possessed of great general culture and re- 

 finement of taste. In his social and moral relations he was 

 marked by rare elevation and purity of character, and has left to 

 the world a standard of excellence in every relation of life which 

 few can hope to attain. 



In accordance with our custom it becomes my duty in quitting 

 the honourable position of President, which I have filled for the 

 past year, to address you upon some theme which shall be ger- 

 mane to the objects of the Association. The presiding officer, 

 as you are aware, is generally chosen to represent alternately one 

 of the two great sections into which the members of the Associa- 

 tion are supposed to be divided, viz , the students of the natural- 

 histovv sciences on the one hand, and of the physico-mathemati- 

 cal and chemical sciences on the other. The arrangement by 

 which, in our organisation, 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 investigates the astronomical, physical, 

 chemical, and biological laws which have presided over the de- 

 velopment of our earth, and while practical geology or geognosy 

 studies its naturrl history, as exhibited in its physical structure, 

 its mineralogy and its palceontology, it will be seen that this com- 

 prehensive science is a stranger to none of the studies which are 

 included in the plan of our Association, but rather sits like a 

 sovereign, commrnding in turn the services of aU. 



As a student of geology, I scarcely know with which section 

 of the Association I should to-day identify myself. Let me 

 endeavour rather to mediate between the two, and show you 

 somewhat of the two-fold aspect w hich geological science presents, 

 ■when viewed respectively from the stand-points of natural history 

 and of chemistry. I can hardly do this better than in the dis- 

 cussion of a subject which for the last generation has afforded 

 some of the most fascinating and perplexing problems for our 

 geological students ; viz., the history of the great Appalachian 

 mountain chain. Nowhere else in the world has a mountain 

 system of such geographical extent and such geological com- 

 plexity been studied by such a number of zealous and learned 

 investigators, and no other, it may be confidently asserted, has 

 furnished such vast and important results to geological science. 

 The laws of mountain structure, as revealed in the Appalachians 

 by the labours of the brothers Henry D. and William K. Rogers, 

 of Lesley and of Hall, have given to the world the basis of a 

 correct system of orographic geology, t and manv of the obscure 

 geological problems of Europe become plain when read in the 

 light of our American experience. To discuss even in the most 



* Address of Prof. T. Sterry Hunt on retiring from the oi!ice of President 

 of ttie American Association for ttie Advancement of Science : abridged 

 from the " American Naturalist." 



t Amer. Jour. Sci., II. xxx. 406, 



summary manner all of the questions which the theme suggests, 

 would be a task too long for the present occasion, but I shall 

 endeavour to-night in the first place to bring before you certain 

 facts in the history of the physical structure, the mineralogy and 

 the palosontology of the Appalichians ; and in the second place 

 to discuss some of the physical, chemical, and biological condi- 

 tions which have presided over the formation of-the ancient crys- 

 talline rocks that make up so large a portion of our great eastern 

 mountain system. 



I. The Geognosy of the Appalachian System. — The 

 age and geological relations of the crystaUine stratified rocks 

 of eastern North America have for. a long time occupied 

 the attention of geologists. A section across nortliern New 

 York, from Ogdensburg on the St. Lawrence to Portland in 

 Maine, shows the existence of three distinct regions of unlike 

 crystaUine schists. These are the Adirondacks to the west of 

 Lake Champlain, the Green Mountains of Vermont, and the 

 White Mountains of New Hampshire. The liihological and 

 niineralogical differences between the rocks of these three regions 

 are such as to have attracted the attention of some of the earlier 

 observers. Eaton, one of the founders of American geology, at 

 least as early as 1832, distinguished in his Geological Text-book 

 (2nd edition) between the gneiss of the Adirondacks and that of 

 the Green Mountains. Adopting the then received divisions of 

 primary, transition, secondary and tertiary rocks, he divided lach 

 of these series into three classes, which he named carboniferous, 

 quartzose, and calcareous ; meaning by the first schistose or argil- 

 laceous strata such as, according to him, might include carbona- 

 ceous matter. These three divisions in fact corresponded to 

 clay, sand, and lime-rocks, and were supposed by him to be re- 

 peated in the same order in each series. This was apparently the 

 first recognition of that law of cycles in sedimentation upon which 

 I afterwards insisted in 1S63.- Without, so far as I am aware, 

 defining the relations of the Adirondacks, he referred to the 

 lowest or carboniferous division of the primai-y series the crys- 

 talline schists of the Green Mountains, while the quartzites and 

 marbles at their western base were made the quartzose and calca- 

 reous divisions of this primary series. The argillites and sand- 

 stones lying still farther westward, but to the east of the Hudson 

 River, were regarded as the first and second divisions of the 

 transition series, and were followed by its calcareous division, 

 whichseemstohave included the limestones of the Trenton group ; 

 all of these rocks being supposed to dip to the westwaid, and 

 away from the central axis ot the Green Mountains. Eaton does 

 not appear to have studied the White Mountains, or to nave con- 

 sidered their geological relations. They were, however, clearly 

 distinguished from the former by C. T. Jackson in 1844, when, 

 in his report on the geology of New Hampshire, he described 

 the White Mountains as an axis of primary granite, gneiss, and 

 mica-schist, overlaid successively, both to the east and west, by 

 what were designated by him Cambrian and Silurian rocks ; these 

 names having, since the time of Eaton's publication, been intro- 

 duced by English geologists. While these overlying rocks in 

 Maine v/ete unaltered, he conceived that the corresponding strata 

 in Vermont, on the western side of the granitic axis, had been 

 changed by the action of intrusive serpentines and intrusive 

 quarizites, which had altered the Cambrian into the Green Moun- 

 tain gneiss, and converted a portion of the fossiliferous Silurian 

 limestones of the Champlain valley into white marbles. t Jack- 

 son did not institute any comparison between the rocks of the 

 White Mountains and these of the Adirondacks ; but the Me.-srs. 

 Rogers in the same year, 1S44, published an essay on the geolo- 

 gical age of the White Mountains, in which, while endeavouring 

 to show their Upper Silurian age, they speak of them as having 

 been hitherto regarded as consisting exclusively of various modi- 

 fications of granitic and gneissoid rocks, and as belonging "to 

 the so called primary periods of geologic time.":): They how- 

 ever considered that these rocks had rather the aspect of altered 

 paleozoic strata, and suggested that they might be, in pare at 

 least, of the age of the Clinton division of the New York system ; 

 a view which was supported by the presence of what were at the 

 time regarded by the Messrs. Rogers as organic remains. Sub- 

 sequently, in 1 847, § they announced that they no longer consi- 

 dered these to be of organic origin, without however retracting 

 their opinion as to the pah-eozoic age of the strata. Reerving 

 to another place in my address the discussion of the geo'ogicai 

 a're of the White Mountain rocks, I proceed to notice briefly the 



• Amer- Jour. Sci., II. x.sxv. 166. 

 t Geology of New Hampshire, 160-162. 

 I Amer. Jour. Sci., II. i. 411. 

 § Ibid, II. v. 116. 



