596 MESOZOIC FLORAS OF UNITED STATES. 



Rhetie to the Middle Cretaceous. Its relations to Sagenopteris on the 

 one hand and Cladophlebis on the other are imperfectly defined. But 

 at all events, whatever its occurrence in the Maryland beds may argue 

 for their age, its occurrence in the Virginia beds must argue the same 

 for them, so that this can not be regarded as evidence that the former 

 are older than the latter. In fact the evidence throughout is all in 

 favor of the practical identity of the age of the Older Potomac in both 

 States. 



One of the unexpected results of this study of the Potomac formation 

 in ]\Iaryland is the deterntination of most of the abundant cones found 

 in so many of the beds as belonging to the extinct genus Athrotaxopsis. 

 This genus was established bj' Professor Fontaine for twigs, leaves, and 

 cones of the Potomac of Virginia that approach most nearly to those 

 of the living Tasmanian genus Athrotaxis of Don. This is placed by 

 Eichler, in the Natiirlichen Pflanzenfamilien of Engler and Prantl, next 

 to the genus Sequoia and between this and Crj'-ptomeria. The cones 

 collected by Mr. Hatcher in the iron shaft near Muirkirk associated with 

 the dinosaurian bones of which so much has been said, are all referred to 

 this genus, and. similar cones occur at Langdon, Riverdale, Contee, Arling- 

 ton, the Howard Brown estate, Hobbs's iron mine. Tip Top, Soper Hall, 

 and Poplar Point, showing that this was the predominant conifer of the 

 region at the time these beds were laid down. Twigs of the same genus 

 also occur at a number of localities, and two species, Athrotaxopsis expansa 

 and A. tenuicaulis are represented. 



Associated with these cones at many places, notably in the ]Muirkirk 

 beds, where the largest number were found, as well as the dinosaurs, 

 are great quantities of silicified wood. Unfortunately this wood has 

 been studied only at a few localities and not at any of those where the 

 cones occur, but wherever it has been studied it has been found to belong 

 to the genus Cupressinoxylon. The structure of the wood of this genus, 

 however, is essentially sequoian, and I had long regarded the Potomac 

 forests as practically those of Sequoia. It is indeed true that Professor 

 Fontaine recognizes the genus Sequoia in several of the Maryland beds, 

 and he refers most of the cones found at Soper Hall, which are larger 

 than those of Muirkirk, l^ut otherwise very similar to them, to S. amhigua 

 Heer. It would seem, therefore, that the great sequoian forests of 



