374 



SCIENCE. 



[N. S. Vol. III. No. 62. 



the name Conodectes favosus may belong to the 

 Diadectidse, but its relationships are at present 

 uncertain. Edw. J. Nolan, 



Recording Secretary. 



GEOLOGICAL SOCIETY OF WASHINGTON. 



At the forty-third meeting of this Society, 

 held at Washington, D. C, February 12, 1896, 

 President S. F. Emmons in the chair, commu- 

 nications were presented as follows : 



Structure o/ the Elk Garden Coal-Fields : By 

 Me. J. A. Taff. The Elk Garden coal-field 

 comprises about one-third of the area of the 

 Piedmont sheet (of Geol. Atlas of United States, 

 U. S. G. S.), and extends about S. 30 W. across 

 its center. This coal-field is limited on the east 

 by the Allegheny front and on the west by the 

 Backbone Mountain. The south branch of the 

 Potomac drains the field from the Grant county 

 line northward, while the southern part is in 

 the basins of Red Creek and Blackwater 

 River. 



In topography as well as in structure the 

 Allegheny front marks the dividing line be- 

 tween the middle or Great Valley and the west- 

 ern or plateau divisions of the Appalachian 

 province. The valley country presents almost 

 level crested mountain ridges, with smooth 

 valleys between and the Allegheny front faces 

 it with an escarpment 1100 to 2000 feet high. 

 The Elk Garden coal-field here represents a 

 part of the plateau region. It is not a smooth 

 plain, but in its nearly flat surface points may 

 be seen in the ridges which extend from the Al- 

 legheny front and Backbone Mountain into the 

 Potomac Gorge. The structure of the valley 

 region is illustrated by the topographic types, i. 

 e., sharp anticlinal folds in the mountain ridges 

 and obtuse, wide and undulating folds in the 

 valleys. 



In the Elk Garden coal-field the topography 

 is more diversified. Both the anticlinal and 

 synclinal folds are occupied by valleys and the 

 mountains are upon their borders. From the 

 crests of Allegheny front and Backbone Moun- 

 tain the dips of the conglomerate are 18° to 25°, 

 but soon decrease and approach the Potomac 

 valley almost horizontally, forming thus an ob- 

 tuse synclinal basin. This basin rises toward 

 the southwest and di\'ides near the center of 



the field, one division following Stony River 

 and Red Creek valleys, while the other extends 

 with the Potomac and passes southwest beyond 

 Fairfax Knob. This division of the main syn- 

 clinal basin is due to a high anticlinal fold 

 which pitches downward between Canaan and 

 and Brown Mountains and is lost in undulations 

 near the center of the field. 



The structure of the Elk Garden coal-field 

 presents the rocks most advantageously for the 

 coal operator. The North Potomac river has 

 severed the five productive coal seams ranging 

 in thickness from four to fourteen feet, so that 

 they incline downwards toward its gorge and 

 and also allow easy access for rail transporta- 

 tion. 



The paper was illustrated by topographic 

 and relief maps and by structure sections. 



Disintegration and Decomposition of Diabase at 

 Medford, Mass. By Geo. P. Meerill. 

 Mr. Merrill described in considerable detail 

 the chemical and physical changes which had 

 taken place in the breaking down of the dia- 

 base at Medford, giving analyses of the fresh 

 and decomposed rock as well as of the portions 

 removed by solvents. The most interesting 

 results brought out were : That the firm rock 

 yielded up nearly S6fc of its constituents to 

 the solvent action of hydrochloric acid and 

 sodium carbonate solutions, as against 32. 3 J^ 

 by the residual sand; further, that in the pro- 

 cess of degeneration some 20 fc of material was 

 lost, the various constituents being removed in 

 the following order, that which suffered most 

 heavily being mentioned first: K^O; CaO; MgO; 

 FczO:,; SiO,; Na^O; PjOj; the alumina, which 

 served as the basis for calculation, being for 

 the time assumed to have remained constant. 



The degeneration was regarded as being 

 mainly postglacial, and as due wholly to at- 

 mospheric agencies. Remarks were made as 

 to the relative rapidity of degeneration in high 

 and low latitudes, Mr. Merrill taking the 

 ground that the apparent greater rapidity of 

 decay in warm latitudes and in forested areas, 

 was due to protection from erosion whereby the 

 disintegrated material was allowed to accumu- 

 late. He, however, believed that there was a 

 difference in kind in the degeneration in high 



