FLORA OF OLDER POTOMAC FORMATION. 365 



From the lowest hdjev I have taken out plants only of a low tj'pe of structure 

 resembling algas and nitellas; from the next laj^er above, equisetffi and fei'ns with 

 strange vine-like structure; from the layer a few feet higher, buds and twigs of 

 trees allied to the cypress and redwoods of California, as also leaves of ferns having 

 the form of those of the Gingko; from the fourth layer other ferns, coniferous stems, 

 buds, and scales, with some leaves of dicotyledons resembling sassafras; and from 

 the upper layer leaves which resemble those of the hawthorn, magnolia, willow, and 

 hemlock. 



The less distinctly stratified clay overlying these is rich in lignite, often con- 

 taining the- trunks and limbs of nearlj^ entire trees, some of which have been found 

 with spruce-like cones and needle-shaped leaves. 



The continuation of this bed upwards is composed of the iron ore clays which 

 form such conspicuous hills and ridges along the road leading to Washington. In 

 this member of the series lie the extensive layers of carbonate of iron, the richest 

 of which occuj" near the base, while the nodules and oxidized lumps are found nearer 

 the surface. The extension of this bed still higher, at various levels, displays the 

 red and white variegated clays, such as we see in large areas in crossing the country 

 south and east of the iron ore hills (see pp. 48, 49). 



It was remarked that the cycadean trunks collected b}^ Tj^son in 

 Maryland were deposited in the museum of the Maryland Academ}' of 

 Sciences. It was there that our party saw them in 1885 and had photo- 

 graphs of them made, to illustrate Professor Fontaine's monograph of 

 the Potomac flora. After the organization of the museum of the Johns 

 Hopkins University the Maryland Academy, being obliged to contract 

 its quarters, donated its paleontological collections to the universit3^ 

 The cycads were transferred among the rest, and are still there. Prof. 

 Wm. B. Clark gave an account of the transfer in 1888," with appropriate 

 acknowledgments . 



The first of Mr. McGee's papers describing "Three Formations of the 

 Middle Atlantic Slope," published early in ISSS,*" is chiefly devoted to the 

 Potomac formation. From it we learn that he had extended his investi- 

 gations much farther to the northeast than had been reached b}' the 

 expedition of 1885, and had studied the contact of the coastal plain 

 with the underlying older rocks through Delaware and Pennsylvania into 

 New Jersey. He referred the "Bryn Mawr gravel" (p. 130), the "ferru- 



Johns Hopkins University Circulars, Vol. VII, No. 65, April, 188S, p. 67. 



b Three Formations of the Middle Atlantic Slope, by W J McGee: Am. Jour. Sci., 3d ser., Vol. XXXV, 

 February, 1888, pp. 120-143; April, 1888, pp. 328-388; May, 1888, pp. 367-388; June, 1888, pp. 448-466, 

 pis. ii and vi. 



