596 MESOZOIC FLORAS OF FNI TFl) STATFS. 



Rlietic to tlio Middle Cretaceous. Its i(>latioiis to Sa<ienopteiis on the 

 one hand and Chidophlehis on the olhcM- ai'e iinpeifectly detined. But 

 at all events, whatever its occuiTence in the Maixland l)eds may argue 

 for their age, its occurrence in tli(> \iiginia l)eds nuist argue the same 

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

 are older than the lattei'. In fact the e\-i(hMicc ihimighout is all in 

 favor of the practical identily of the age of I lie Older Potomac in both 

 States. 



One of the unexjK'cted results of this stud\- of tlie Potomac formation 

 in ^larvland is the determination of most of the abundant cones foinid 

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

 This genus was established b>- 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 {)laced by 

 Eichler. in the Xntiirlichen Pflanzenfamilien of Engler and Prantl. next 

 to the genus Sequoia and between this and Cryptomeria. The cones 

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

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

 this genus, and similar cones occm- 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 pretloininant 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, Athrola.ropsis e.vpattsa 

 and A. tenuicaidis are represented. 



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

 beds, where the largest numl)er 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 gemis Setjuoia in several of the Maryland beds, 

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

 than those of Muirkirk, but othenvise very similar to them, to S. ambigua 

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



