L. F Ward — Evidence of the Fossil Plants, etc. 119 



Owing to the small amount of vein material which was avail- 

 able for chemical analysis and the impossibility of separating it 

 completely from the enclosing rock, the results obtained can 

 be regarded only as suggestive. The main points brought out 

 can be best shown by reproducing here a comparison of the 

 results : 



Mass of meteorite. 



Si0 2 = 



37-70 



Fe 



4-41 



FeO 



23-82 



A1 2 3 



2-17 



CaO 



2-20 



MnO 



•45 



MgO 



25-94 



NiCo 



1-75 



s 



1-30 



Vein material, 



38-96 



230 



22.98 



1-89 



trace 



27-52 



3-26 



•26 



Sp. gr. = 3-510 Sp. gr. = 3-585 



These differences are too slight to be considered of great 

 value until found to be constant by further investigation. It 

 is to be hoped that the ultimate possessor of the stone will re- 

 gard a knowledge of its true character as of first importance 

 and will not hesitate to sacrifice any necessary amount for the 

 purpose of an exhaustive examination by the most advanced 

 methods. Our most sincere thanks are due Mr. Hensoldt for 

 kindly furnishing us with the information regarding the dis- 

 covery of the meteorite. 



Washington, D. C, April 12th, 1888. 



Art. XIII. — Evidence of the Fossil Plants as to the Age of 

 the Potomac Formation;* by Lester F. Ward. 



It is remarkable that the geologic age of the formation 

 upon which the cities of Baltimore, Washington, Fredericks- 

 burg and Richmond stand should have remained unknown to 

 the present day. My contribution to this subject relates en- 

 stance as the meteorite itself, and an opaque, half glassy black admixture resem- 

 bling the black vein-like material of the Orvinio stone. The silicates occur in the 

 vein in the form of* small sharp splinters, the iron in granules and the pyrrhotite 

 in the form of little leaves and small kernels, often so arranged as to give rise 

 to a fluidal structure. Dr. Hans Reusch has described (N. Jahrb. fur Min., iv 

 Beil. Band., 3d heft, 1886. pp. 491-2), veins in the Stalldalen meteorite which 

 present features in part common to those of the Fayette stone. To the unaided 

 eye the filling material is black and opaque and carries metallic particles. Under 

 the microscope it shows a brownish gray, isotropic and sometimes opaque glassy 

 substance densely crowded with rounded transparent fragments. The upper fig- 

 ure in his Plate XIV closely resembles in structure the vein matter of the Fay- 

 ette stone, but as far as c;m be judged from his description the included particles 

 seem to have retained their normal optical properties. Reusch regards this black 

 vein material as the result of a partial refusion of the ehondrite substance. 



* Read before the .National Academy of Sciences at Washington. April 20, 

 1888. 



