36 INTRODUCTION. 



Stur ' has pointed out the close similarity between the Lunz flora 

 of Austria and the Rhaetic flora of Virginia. Perhaps the most 

 striking example of a type identical with, or at least very nearly 

 allied to, a Lower Oolite species is afforded by some fronds referred 

 by Fontaine to the genus Acrostichites. In his description of 

 plants from Virginia, Bunbury 2 expressed the view that as regards 

 the evidence afforded by the fossil plants the strata might be 

 referred with almost equal plausibility to either the Triassic or 

 Jurassic series. 



Equisetites Rogersi, Schimp. (considered by Rogers identical with E. columnaris 



from Brora in Sutherlandshire 3 ) ; cf . Equisetites columnaris, Brongn. 

 Macrotceniopteris magnifolia, Hog. ; cf. Tteniopteris major, L. & H. 

 jicrostichites linnacefolia, Hog. N 



A rhombifolius .Font. f> . Williamsoni (Brongn.). 



A. densifolius, Font. j 



Cladophlebis microphylla, Font. ' 



Podozamites Emmonsi, Font. ; cf. P. lanceolatus (L. & H.). 

 Ctenophyllum Braunianum, Gb'pp. ; cf. Dioonites sp. 



Asteroearpus virginiensis, Font, (fertile fragment) ; cf. Cladophlebis denticulata 

 (Brongn.). 



The numerous plants described by Fontaine in a later monograph 

 on the Potomac or younger Mesozoic flora 4 consist for the most 

 part of "Wealden and other Lower Cretaceous species, but Jurassic 

 forms are also represented. 5 The ' Potomac flora ' of Virginia 

 and Maryland is in reality made up of floras varying in age from 

 Upper Jurassic to the upper members of the Lower Cretaceous, 

 and does not represent a single flora marking one definite geological 

 horizon. It is unnecessary to attempt a detailed analysis of the 

 species described by Fontaine. Several of the plants agree with 

 European Wealden types, others point to a higher horizon, and 

 there are a certain number which may be compared with Lower 

 Oolite species. It is very difficult to institute any exact comparison 

 between the Virginian and the East Yorkshire plants without 

 access to the specimens themselves ; the illustrations in Fontaine's 

 monograph hardly do justice to the rich material, and the excessive 



1 Stur (88 1 ). 



2 Bunbury (47), p. 288. 



3 Fontaine (83), p. 12. 



4 Fontaine (89). 



5 Vide also Ward (95) (96) (97), and Marsh (98). 



