OLDER POTOMAC OF VIRGINIA AND MARYLAND. 535 



shaft being then filled with water. This collection was made by Lester 

 F. Ward, David White, and Robert T. Hill. They obtained 42 of the 

 cones, but these are less perfect than the others. 



In 1893 Mr. Arthur Bibbins collected 1 specimen. No. 6342 of the 

 Woman's College of Baltimore, and in June, 1895, he obtained for the 

 State Geological Survey of Maryland 5 more of these same cones. These 

 bear the number 5709 of that survey. On still another occasion he 

 "oUected what seems to be a cycadaceous fruit. 



The cones all seem to belong to Athrotaxopsis expansa, and the 

 cycadaceous fruit is probably Cycadeospermum acutum. 



Athrotaxopsis expansa Fontaine. 



PI. CIX, Figs. 12, 13. 



1889. Athrotaxopsis expansa Font.: Potomac Flora (Monogr. U. S. Geol. Survey, 

 Vol. XV), p. 241, pi. cxiii, figs. 5, 5a, 5b, 6; pi. cxv, fig. 2; pi. cxvi, fig. 5; 

 pi. cxvii, fig. 6, pi. cxxxv, figs. 15, 15a, 15b, 18, 22 (cones). 



As already remarked, the cones collected by Mr. J. B. Hatcher 

 came from the clay which yielded the dinosaurian remains described 

 by Professor Marsh from the Potomac strata of Maryland. These 

 dinosaurian fossils led Professor' Marsh to maintain that the Potomac 

 formation of Maryland is of Jurassic age. The cones now in question 

 are of additional interest on account of their unusual mode of fossili- 

 zation. They are mud casts, and in most cases retain no trace of the 

 original vegetable matter. They vary a good deal in size, but all seem 

 to belong to the one species, Athrotaxopsis expansa. The largest are 

 18 mm. by 15 mm., and the smallest are not more than half as large. 

 The difference in size is probably due to a difference in their develop- 

 ment. They are often somewhat distorted from pressure. The normal 

 shape seems to have been broadly oblong, but some are nearly spher- 

 ical. The fossil is composed of indurated mud deeply pitted with 

 depressions that sometimes take the exact form of the cone scales, 

 and the whole object retains pretty accurately the shape and size of 

 the original cone. Sometimes the pits retain a trace of carbonaceous 

 matter, from the vanished scale, lining the pit. The pits were evidently 

 caused by the decay of scales which persisted until the cone had been 

 outlined in mud. These cones are exactly like those of Athrotaxopsis 



