September 11, 1885.] 



SCIENCE. 



221 



rences, it exhibits an orderly series of modifications 

 which are parallel in different sections. Though its 

 record is discontinuous at any one locality, the life of 

 the fauna was continuous somewhere, its distribution 

 at every epoch being determined by ever-shifting 

 physical conditions. Within tlie field of study are 

 seven distinct faunas: A, the middle Devonian, or 

 general Hamilton, fauna; B, the fauna of the black 

 shales; C, the fauna of the green shales of the Portage 

 group; D, the fauna of the brown shales and sand- 

 stones of the Chemung group ; E, the fauna of the 

 Panama conglomerate; F, the fauna of the Catskill 

 rocks ; G, the fauna of the Waverly group. In each 

 of these, except E and F, from three to seven varia- 

 tions are recognized, which have a saccessional order, 

 and are designated ' stages.' In presenting his mate- 

 rial, Professor Williams defined each stage, and 

 assigned it a symbol, consisting of a letter and a num- 

 ber. A chart exhibited the local stratigraphic col- 

 umns drawn to scale, and in their proper geographic 

 relations, lithologic distinctions being expressed by 

 colors, and the faunal horizons indicated by their 

 symbols, — a system of graphic presentation which 

 greatly aided the audience in comprehending the 

 author's numerous inductions. 



Prof. S. G-. Williams reported observations on the 

 shore of Cayuga Lake, at the outlet of Skaneateles 

 Lake, and at Oriskany Falls, leading to the conclu- 

 sion that lower Helderberg rocks, other than those of 

 the water-lime group, have a greater westward exten- 

 sion in Xew York than has heretofore been supposed. 

 Prof. James Hall called attention to the uniformity of 

 conditions indicated by the stratigraphic series in cen- 

 tral New York, as compared with the varied history 

 deducible from the exposures on the Hudson River; 

 and Prof. J. P. Lesley spoke of the ' infinite variability ' 

 of the Oriskany. Pennsylvania contains a thousand 

 miles of its outcrop, in which its thickness oscillates 

 from five hundred feet to nothing at all; and no two 

 sections agree. Mr. A. S. Tiffany gave an account 

 of the corniferous group as it is exhibited in Scott 

 county, Iowa, and in Rock-Island, 111. ; and also of 

 a yellow sandstone at Burlington, lo., which he re- 

 fers, with doubt, to the Chemung. From the first 

 he reported 246 species of fossils, and from the second 

 84 species. 



The problem of the origin of the paleozoic sedi- 

 ments of Pennsylvania was discussed by Prof. E. W. 

 Claypole. Postulating that the material came from 

 a belt of Archaean rocks now exposed — or known 

 to underlie later formations — in south-eastern Penn- 

 sylvania, and adjacent portions of New Jersey and 

 Maryland, he based a computation on the area and 

 known thickness of the sediments, and the area of 

 the assumed district of derivation; and reached the 

 conclusion that the Archaean district had suffered a 

 denudation of several vertical miles. Then, restrict- 

 ing attention to the conglomerates of the paleozoic 

 area, he showed, that, on a moderate estimate, 36,000 

 square miles of sediment contain an average of thirty 

 feet of vitreous, milky quartz, in the form of pebbles. 

 In the rounding of these by attrition, a still greater 

 quantity of quartz was disposed of; so that a truly 



immense amount must have existed in the district of 

 denudation. The visible Archaean outcrops contain 

 only a small amount of such quartz, and that is almost 

 confined to a narrow belt of Huronian rocks in 

 Pennsylania. It is probable, therefore, that the Hu- 

 ronian was better represented in the eroded mass of 

 Archaean than it is in the surviving outcrops. 



Prof. Lewis E. Hicks described the structure and 

 relation of the Dakota group in Nebraska, main- 

 taining that the actual eastern shore of the Dakota 

 Sea is there recorded. The formation rests on an 

 eroded surface of subcarboniferous limestone, the 

 valleys of which were occupied by bays and gulfs of 

 the Dakota Sea. It is noteworthy that the lines of 

 post-carboniferous drainage were identical with the 

 main lines of modern drainage, though the streams 

 flowed in the opposite direction. It thus happens, 

 that, despite the westerly dip, the eastern boundary 

 of the Dakota has its salients in the east-sloping val- 

 leys of the existing topography. The average thick- 

 ness of the formation is 400 feet : its average dip is 

 six feet to the mile in the direction N. 70° W. It 

 is not entirely, nor even predominantly, composed 

 of sandstone,but contains a large amount of shale, 

 with fire-clays, and, near the top, some lignite. 



The first communication on the drift was the open- 

 ing paper of the session, and introduced to the atten- 

 tion of the section the features of the local geology. 

 As the phenomena Prof. A. Winchell described have 

 long since passed into geologic literature, they need 

 not be recited here ; but he touched on a local eco- 

 nomic subject which is well worthy of promulgation. 

 Citizens of Ann Arbor have culled from the fields the 

 larger crystalline erratics; and, breaking them into 

 suitable shape, have built of them their finest edifices, 

 public and private. The stones exhibit a variety and 

 individuality which no quarry can rival; but the pre- 

 vailing flesh-tints and grays blend harmoniously, 

 and the effect is peculiarly agreeable to the eye. 

 Prof. A. H. Worthen described the quaternary de- 

 posits of central and southern Illinois, taking for his 

 text the sections afforded by a number of coal-shafts 

 traversing the superficial deposits. The bed-rock 

 surface is diversified by valleys very much as is the 

 drift-surface above, but with a different drainage 

 system. The drift-section is, therefore, variable in 

 thickness, but the sequence of its members is ap- 

 proximately uniform. At bottom is a stratified clay, 

 in part gravelly; and, as judged by its composition, 

 this is derived from the waste or decay of the bed- 

 rock of the immediate vicinity. Then comes a forest- 

 bed — not a universal feature, but so widely spread 

 as to render the well-water of large districts unfit for 

 use. Over this lies a blue and yellow gravelly clay, 

 with glaciated bowlders ranging up to two feet in 

 diameter; then a few feet of loess, and finally a thin 

 bed of fine clay. These deposits do not point to gla- 

 cial ice alone as an agent. They indicate water also, 

 and the lowest member is either sedimentary or allu- 

 vial. Prof. John C. Branner gave an account of the 

 glaciation of the Lackawanna valley, where the same 

 rock-surfaces bear striae in systems diverging from 

 20° to 40,° and in one instance even 120°. These are 



