FLORA OF OLDER POTOMAC FORMATION. 399 



Freezeout Hills of Wyoming, and in a "Postscript" to this paper he 

 considers these in the same connection and correctly says that they 

 came from the Jurassic. This he claimed to sustain his view of the 

 Jurassic age of the cycads of the Black Hills and of the Potomac. I 

 came into possession a few months later of a much larger collection 

 of these Jurassic cycads and fully described and illustrated them. It 

 turned out that they all belonged to a different genus (Cycadella) from 

 the rest, which seems to be characteristic of the Jurassic trunks. 



It remains to mention the second paper of Messrs. Clark and Bib- 

 bins, read, before the Geological Society of America on December 31, 

 1901," in which they again go over the same ground in much the same 

 way, but do not greatly increase our knowledge of the formation and 

 do not materially change the conclusions reached in the paper last 

 treated. 



Before this paper was read Professor Fontaine had sufficiently 

 advanced with his work of determining the plants to make it certain 

 that there was no part of the Potomac of Maryland that does not yield 

 dicotyledonous plants. The statements made in this paper relative to 

 the flora do not seem to be based upon data obtained by consultation 

 with him, but are practically repetitions of the erroneous statements 

 made in the previous paper. For example, after stating (p. 192) that 

 "the flora of the Patuxent formation includes equisetse, ferns, cycads, 

 conifers, monocotyledons, and a very few archaic dicotyledons, the 

 coniferous and cycadean element being particularly strong," they say 

 (p. 195) that "the flora of the Arundel formation includes algse, fungi, 

 lycopods, ferns, cycads (apparently fronds only), many conifers and 

 monocotyledons, as well as a considerable showing of dicotyledons, 

 which, though not specially advanced in type, are far beyond those 

 of the Patuxent formation in grade as well as in variety and numbers. 

 There is therefore a well-defined contrast between the dicotyledonous 

 elements of these two formations." These statements are certainly 

 premature and seem to be purely theoretical, based on the assumption 

 of the greater age of the Patuxent, which is not borne out by its meager 

 flora. So far as the trunks of cycads are concerned, they occur^ accord- 



« Geology of the Potomac group in the middle Atlantic slope, by W. B. Clark and A. Bibbins: Bull. Geol. 

 See. America, Vol. XIII, July 29, 1902, pp. 187-214, pi. xxii-xxviii. 



