206 RECORD OF SCIENCE FOR 1886. 



their horizons, equiv^aleucy, aud former extent. He calls atteutiou to 

 some iuterestiog facts uot generally appreciated in regard to the west- 

 ward thinning of the Paleozoic series. In central Pennsylvania the 

 thickness of the Paleozoic rocks from the top of the Potsdam to the toj) 

 of the Pottsville conglomerate is 26,000 foet and in central Ohio only 

 3,500 feet, and there is a similar thinniug northward. Between the edge 

 of the Alleghany Monntains, in Huntington County and Pittsburgh, the 

 lower members of the Carboniferous system thin to one half. In dis- 

 cussing the flexures of the coal district, discrimination is made between 

 the great low rolls and the gentle plications of some of the Western 

 basins. The former are thought to be part of those of the general Ap- 

 palachian system, but the latter appear to be due to local subsidence at 

 the time of the deposition, and by the shrinkage due to the compacting 

 of the loose mass of organic matter now pressed into coal.* 



55. D'Invillierst gives a preliminary account of the general re-exam- 

 ination of the Pittsburgh coal region, describing in detail a portion of 

 Alleghany County. He sjieaks highly of the work of his predecessors, 

 who determined the more general features, but it is now proposed to 

 prepare contour maps of the coal beds, and very detailed work is con- 

 templated. 



5G. McCalley reports on the study of the Warrior coal field of Alabama, 

 and describes many details of its coal beds, structure, drift cover, soils, 

 topography, etc. The Warrior field is stated to be a broad, shallow, 

 tray-shaped depression, sloping southwesterly under the newer forma- 

 tions, and much flexed and dislocated on its southeastern part. It is 

 principally composed of sandstone, conglomerates, shales, slates, aud 

 coal seams, with occasional beds of limestone. The country is plateau 

 where underlain by the conglomerates, and this holds coals which thin 

 southward. It is thought that in the basin district near Tuscaloosa 

 there are 300 feet of coal measures, with nearly fifty seams of coal, aggre- 

 gating 100 feet in thickness, and varying from a few inches to 14 feet 

 each. Thirty-five are known to be 18 inches or over in thickness aud 

 fifteen over 2i feet. They are thickest in the center of the basin and 

 thin northwestward. I 



57. Hill calls atrention to the very exceptional occurrence of coal in 

 the Carboniferous of Colorado. The coal is anthracite, and in very thin 

 beds, probably in the Middle Carboniferous. § 



58. Hicks, II in a paper on the Permian of Nebraska, provisionally ap- 

 plies the term to a group of strata along the valley of Blue River in 

 Gage County. They consist of less than 200 feet of magnesian lime- 



* American lust. Mining Eng., Trans., 1886. 



t Secoufl Geological Survey of Pennsylvania, Annual Report for 1885, pp. 125-221. 



I Alabama Geol. Survey, Report on Warrior Coal Field, pp. 571-80. 1886. 

 $ Colorado Sci. Soc, Proc, vol. 2, pp. 25-26. 



II American Naturalist, Oct., 1886, vol. 20, pp. 881-883; Am. Assoc, Proc, vol. 35, 

 pp. 216-217. 



