September 26, 1884.] 



SCIENCE 



327 



of time, but also geographically according to the 

 areas of their distribution. The influences which 

 brought about a change in the character of the sedi- 

 ments deposited, also manifested themselves in alter- 

 ing the forms of the organisms inhabiting these 

 sediments. 



Mr. Ashburner said that the gradual creeping up- 

 ward of fossil forms characteristic of one horizon into 

 overlying strata was well borne out in western Penn- 

 sylvania. In the oil regions, Chemung forms are 

 often met with in a well-defined Catskill fauna. 

 Professor Claypole considered a gradual transition 

 between two formations as quite the rule, and pro-, 

 posed to call beds of this character between the two 

 horizons especially under discussion, ' Catskill-Che- 

 mung.' To such a designation Professor James Hall 

 strongly objected ; maintaining that each formation 

 was quite distinct, and that, while there might be an 

 alternation or even commingling of beds belonging 

 to both, no such indiscriminate mixture of typical 

 forms as that described by Professors Williams and 

 Claypole was possible. He would hardly be willing 

 to admit the occurrence side by side at that horizon 

 of Spirifer disjuncta and Spirifer mesostrialis, to 

 which allusion had been made. Two papers by Pro- 

 fessor Hall may be mentioned here, since they bear 

 directly on this discussion, although they were not 

 read until two days later. In the first of these, on 

 the intimate relations of the Chemung and Waverley 

 groups in north-west Pennsylvania and south-west 

 New York, it was shown that the apparent commin- 

 gling of the Chemung and Catskill faunas is due to 

 the fact that the sea-bottom gradually approached the 

 surface, and thus locally gave rise to dry land. The 

 gray Chemung, rocks contain a marine fauna; while 

 the red Catskill beds carry almost altogether land 

 and fresh-water forms, although some Chemung ani- 

 mals survived for a time under the altered condi- 

 tions. These alternations sometimes extend through 

 three hundred feet. The second of Professor Hall's 

 communications described the recent discovery in 

 considerable numbers of the Eurypteridae, a family 

 especially characteristic of Silurian rocks, in carbon- 

 iferous beds. These widely separated occurrences 

 are connected by a single known specimen of Euryp- 

 terus from the Chemung formation. 



The first of a series of papers relating to the crys- 

 talline rocks was read by Professor Roland D. Irving 

 of Madison, Wis. It treated of metamorphism in the 

 Huronian of the north-west; although, according to 

 the author, such metamorphism can scarcely be said 

 to exist at all. The terms metamorphism and Hu- 

 ronian were first defined, and then the rocks consid- 

 ered as belonging to this formation in the vicinity of 

 Lake Superior were classified in five categories. 

 These were : 1° quartzites and graywackes; 2° basic 

 massive rocks; 3° acid massive rocks; 4° cherts and 

 limestones; and 5° hornblende, mica, and chlorite- 

 schists. Each of these categories was then considered 

 in succession, and shown not to be metamorphic in 

 the sense of being sedimentary material re-crystal- 

 lized in situ. 



Prof. C. H. Hitchcock next presented thirteen 



sections across the states of Vermont and New 

 Hampshire. These were constructed to show the 

 anticlinal structure of the Vermont gneiss, which 

 their author now considers to be established beyond 

 doubt. The gneiss has the same lithological charac- 

 ter as that occurring in the White Mountains, where 

 it is of Laurentian age. As is well known, the 

 structure of Vermont has generally been regarded as 

 synclinal; and if the conclusions of Professor Hitch- 

 cock prove correct, they certainly have a most impor- 

 tant bearing upon the much-discussed problems of 

 New-England geology. If, as he asserts, the Ver- 

 mont gneisses underlie the Huronian schists, which 

 extend in a V-shaped area from Canada southward 

 along the border between Vermont and New Hamp- 

 shire, then they must be the oldest rocks of the 

 region, instead of metamorphosed Silurian or Cam- 

 brian sediments, as they are at present more generally 

 considered. 



No more important contribution has ever been 

 made to the vexed question of metamorphism and 

 the origin of the crystalline schists than the recently 

 published work of Dr. Johannes Lehmann, now 

 professor in the university of Breslau, entitled ' Un- 

 tersuchungen fiber die entstehung der altkrystallinen 

 schief ergesteine,' Bonn, 1884. This elegantly printed 

 book is accompanied by a superb atlas of photo- 

 graphic plates most satisfactorily illustrating rock 

 structures, and was brought to the notice of the 

 association by Dr. George H. Williams of the Johns 

 Hopkins university, who proceeded briefly to review 

 its contents. The most important point brought 

 out by Lehmann is the influence of pressure in the 

 metamorphism of rocks. The great orographic 

 forces which have crumpled the strata have also 

 greatly changed their original form, rendering sedi- 

 ments crystalline and compact, \^hile they developed 

 in homogeneous eruptive masses a schistose or even 

 banded structure. Thus bedding in crystalline rocks 

 is not to be regarded as necessarily a sign of sedimen- 

 tation, nor is the lithological character of a rock any 

 definite criterion of its age. Professors Carvill Lewis 

 and Hitchcock remarked that these ideas agreed 

 perfectly with what they had observed in the highly 

 crystalline areas which they had particularly studied; 

 and Dr. Williams gave an account of an eruptive 

 mass near Baltimore, in which both changes in 

 mineralogical composition, and the development of 

 a schistose structure, had been accomplished by 

 pressure. 



Professor Alexis Julien of New York communi- 

 cated the results of a very extended study of the 

 Eozoon canadense from nearly all the localities where 

 it has thus far been found, adding other localities of 

 his own discovery. The result of his investigations 

 led him to decide in favor of the inorganic nature of 

 the so-called fossil, although his ideas in regard to 

 the mode of its formation differ considerably from 

 any heretofore advanced. He noticed as universal 

 in all localities, that the calcium and magnesium 

 carbonates were very unequally distributed in the 

 eozoonal limestones; and, that there was a large 

 development of pyroxene where the dolomite was 



