942 



SCIENCE. 



[N. S. Vol. XVII. No. 441. 



Virginia and the principal localities repre- 

 sented in the collections were shown by maps. 

 The entire review, with Professor Fontaine's 

 reports, and numerous plates, will be published 

 shortly as a professional paper of the U. S. 

 Geological Survey. 



I'Ir. M. E. Campbell : ' Pocono Eocks in the 

 Allegheny Valley.' 



Eeeently Mr. David White and Mr. Camp- 

 bell obtained fossils from the Allegheny Val- 

 ley which show (1) that Pocono rocks having 

 a thickness of at least 130 feet are present in 

 Armstrong County, Pa.; (2) that the Potts- 

 ville is 140 feet in thickness and consists of 

 the Homewood and Connoquenessing sand- 

 stones separated by the Mercer coal group; 

 and (3) that the well-marked Pocono and 

 Pottsville are separated by a mass of sandstone 

 and sandy shale having a thickness of about 

 80 feet and apparently barren of fossils. Al- 

 though these beds can not be classified 

 definitely, there are some reasons for referring 

 them to the Pocono. If this reference is cor- 

 rect the Mauch Chunk shales and Sharon 

 conglomerate are absent and the Connoquenes- 

 sing sandstones rest directly on rocks of 

 Pocono age. 



Mr. David White : 'Age of the Mercer Group.' 



Under this title Mr. White communicated 

 certain conclusions and correlations resulting 

 from the study of the fossil plants of the 

 group. He described the pteridophytes of the 

 Mercer flora as a mixture of distinctly upper 

 Pottsville elements with the earliest, and 

 often slightly archaic, representatives of the 

 common species of the Allegheny. Consider- 

 able change is noted between the plants in 

 shales resting on the top of the Connoquenes- 

 sing at certain localities and those im- 

 mediately underlying the Homewood sand- 

 stone at others, the duration of Mercer time, 

 as indicated by the floras, being greatly dis- 

 proportioned to the relatively small thickness 

 of the group in Pennsylvania and Ohio. Such 

 a comparative duration is, however, in part 

 suggested by the composition of the group, 

 which embraces coals, limestones, iron ores 

 and fire-clays in the northern region. The 

 associated fossil plants indicate that the re- 

 fractory or ' flint ' clays worked at many points 



in Somerset, Cambria, Centre, Clearfield and 

 Jefferson counties, as well as the famous 

 Mount Savage clays in western Maryland, be- 

 long to the Mercer group, which is shown to 

 be the stage of a belt of refractory fire-clays 

 extending irregularly from the Potomac basin, 

 in northern West Virgina, northward around 

 the border of the main bituminous field 

 through McKean County and as far as St. 

 Charles on Eed Bank Creek in northern Arm- 

 strong County. 



The Mercer group is correlated by the au- 

 thor of the paper with the lower stage of the 

 Westphalian (Sudetic) or the Lower Coal 

 Measures of Europe. The more complete 

 knowledge of its flora throws much light on 

 the age of the Kanawha formation in the 

 southern Virginia regions, additional collec- 

 tions from which have recently been examined. 

 In a discussion of the age of the Kanawha 

 in 1899, the speaker had shown that the greater 

 portion, embracing not less than 600 feet, of 

 the formation, antedated the Allegheny for- 

 mation, although the northern equivalents of 

 the formation were not deiinitely known. It 

 now appears that its partial equivalence with 

 the Mercer, then conservatively proposed, is 

 conclusively shown by the plants, and that a 

 great portion of the Kanawha formation is to 

 be regarded as the southern extension of the 

 Mercer group. The further study of the 

 floras indicates not merely that the middle of 

 the formation may be of Mercer age, but that 

 beds up to within 125 feet of the ' Black 

 Flint ' are clearly referable to the latter group, 

 while the basal Allegheny time boundary is 

 probably very much nearer the level of the 

 Black Flint. 



During the evening of May 13 a special 

 meeting was held in continuation of the 140th 

 regular meeting, which was devoted to a dis- 

 cussion of the ' Quantitative Classification of 

 Igneous EoeliS.' No formal papers were pre- 

 sented, but the practical workings of the new 

 classification were commented upon by sev- 

 eral petrogTaphers who had tested it, and ob- 

 servations, critical and commendatory, from 

 foreign workers were read and discussed. 

 W, C. Mendenhall, 



Secretary. 



