416 



SCmNGE. 



[N. S. Vol. V. No. 115. 



occurring in the Greenland Cenomanian. 

 These Cenomanian tj^pes are probably to be 

 regarded as precursors not yet fully estab- 

 lished, just as the Jurassic types must be 

 considered as survivors not yet extinct. 



" The angiosperm plants present in the flora 

 are much more important in giving a more recent 

 fades to the flora. They show quite a large 

 number of species, but these are almost al- 

 ways local in occurrence, and are repre- 

 sented in most instances by few individuals. 

 In a number of cases only one or two speci- 

 mens were found. It has been generally held 

 that any considerable development of angiosperms 

 in a fossil flora is strong, indeed conclusive, evi- 

 dence that its age is not greater than that of the 

 Cenomanian. But apart from the evidence 

 given by the older and predominant ele- 

 ments of the flora, there is reason to think 

 that the Potomac flora is older than Ceno- 

 manian, even if we take into consideration 

 the angiosperms alone. 



' ' The conclusion above mentioned is based 

 solely upon the fact that in no flora older than 

 Cenomanian has any considerable angiosperm 

 element been found up to the present time, but 

 various writers have with justice maintained 

 that it is improbable that the apparently 

 sudden appearance of angiosperms in great 

 force in the Cenomanian represents the true 

 state of the case. It is highly probable that 

 they had numeroxis precursors and ances- 

 tors, which existed in the ISTeocomian, and 

 perhaps some of them, at least, in the Ju- 

 rassic. It is probable that some of the forms 

 called Protoi'hipis are ancient angiosperms. 

 The existence then of numerous angio- 

 sperms in a flora which is predominantly 

 Neocomian, but which contains many sur- 

 viving Jurassic types, is just what we would 

 expect to find. But we have direct evidence 

 of the existence of angiosperms in the Neo- 

 comiau. Heer has described from the Kome 

 beds of Greenland, which are Urgonian in 

 age, an angiosperm which he called Popidus 

 primmva. Only a few specimens were found. 



This single occurrence has remained so long 

 unsupported by other discoveries of angio- 

 sperms in the Neocomian that doubts have 

 been expressed concerning the correct local- 

 ization of these specimens. It was thought 

 possible that they really came from a 

 younger flora. If the Potomac flora is in 

 fact Neocomian, we have in this case a note- 

 worthy illustration of the truth that posi- 

 tive evidence, however scanty, should out- 

 weigh any amount of negative evidence. 



" The Potomac angiosperms in their gen- 

 eral character give evidence of an age 

 greater than Cenomanian. It is true that 

 we find in them genera, and possibly some 

 species, that survive into the Cenomanian 

 and even down to the present time, but 

 taken as a whole they form a peculiar group, 

 totally unlike the floras of the Dakota and the 

 Amboy beds. It is in the flora of the Dakota 

 group, and the Amboy clays of New Jersey, 

 especially the latter, that we would expect 

 to find the greatest number of plants iden- 

 tical with Potomac forms. Both of these 

 floras are Cenomanian probably, and the Amboy 

 flora, so far as yet knoiun, is the one that comes 

 next above the Potomac. There are one or two 

 species that are probably common to the 

 Potomac and the Dakota beds, or that are 

 nearly allied, but they are long-lived types, 

 that come down to the present time with 

 little modification. 



" By the kindness of Dr. J. S. Newberry, 

 who studied and described the New Jersey 

 Amboy flora, I have been enabled to ex- 

 amine a large number of drawings of the 

 New Jersey plants. These plants are totally 

 different from those of the Potomac. It is not 

 certain that a single species survives from the 

 Potomac into the Amboy beds. What is even 

 more significant, even the genera that are most 

 abundant in the Potomac and most characteristic 

 of that formation have no representative in the 

 New Jersey flora. It is clear that a very im- 

 portant gap exists between these two floras, and 

 that an interval of time separates them, in which 



