Sinnott and Bartlett — Coniferous Woods. 291 



New Jersey, which is not the same as, but nevertheless closely 

 resembles, the one found in the Potomac beds at Washington. 

 It is also different from either of our fossils. The " Sequoia " 

 (Geinitzia) form, moreover, is rare in the deposits, as is also 

 Sphenolepis. There remain only Nageiopsis and Arthrotaxop- 

 sis to be considered. 



Of these two genera, both of which are abundant, Nageiop- 

 sis closely resembles certain of the living broad-leaved Podo- 

 carpineae and has always been regarded as belonging to this 

 family. The fact that one of the wood types associated with 

 it bears anatomical evidence of membership in the same group 

 makes very reasonable the conclusion that Podocarpoxylon 

 McGeei is indeed the wood of a species of Nageiopsis. 



If this is the case, a relationship is at once suggested between 

 Arthrotaxopsis and Paracupressinoxylon potomacense. A 

 study of the internal and external structure of related types 

 renders this conclusion even more probable. Arthrotaxopsis 

 belongs to the large group of Mesozoic conifers which includes 

 Brachyphyllum, Geinitzia, Thuyites, Sphenolepis, Widdring- 

 tonites and other similar types. It is perhaps most closely 

 related to the last two genera mentioned. A study by Hollick 

 and Jeffrey (1. c.) of the internal structure of specimens referred 

 to certain of these genera indicates that Brachyphyllum, Gei- 

 nitzia, Widdringtonites and a species formerly included under 

 Frenelopsis (but placed by them in a new genus, Raritania) are 

 araucarian rather than cupressineous in their affinities. Since, 

 as we have already shown, evidence from internal structure 

 favors the relationship between Paraoupressinoxylon poto- 

 macense and the wood of these microphyllous conifers, the 

 conclusion is highly probable that in this fossil we possess the 

 wood of one or more species of Arthrotaxopsis. This genus is, 

 therefore, to be added to the increasing array of small-leaved 

 coniferous Mesozoic fossils which are presumably araucarians 

 in disguise. 



Much is to be said in favor of the general contention that a 

 large flora both of podocarps and small-leaved araucarians 

 existed in Jurassic and Cretaceous times, but in the present 

 state of our knowledge such a view can not yet be regarded as 

 definitely established. If the wholesale reference of small- 

 leaved impressions and of Cupressinoxyla to the Araucarineae 

 is correct, it renders rather improbable the existence of a very 

 extensive flora of true Cupressineae in the Mesozoic, and favors 

 the view that this group was rather late in making its appearance. 



Summary. 



1. The present paper records a study of certain lignites and 

 charcoals from the Patuxent horizon of the Potomac forma- 



Am. Jour. Sci. — Fourth Series, Vol. XLI, No. 243. — March, 1916. 

 21 



