194 J. S. Newberry— Flora of the Great Falls Coal Field. 



group in doubt, but his opinion seems rather to incline to a 

 Jurassic date. Professor O. C. Marsh considers the Potomac 

 group Upper Jurassic, because he has obtained from it a num- 

 ber of reptilian remains of decided Jurassic affinities, but he 

 tells me there are no species which he can identify with those 

 of the Jurassic system, and we have been hitherto with little 

 or no information about the vertebrate fauna of the Lower 

 Cretaceous rocks of Xorth America ; so we need not be sur- 

 prised to find it exhibiting marked Jurassic affinities. As 

 pointed out by Professor Marsh the low grade and Mesozoic 

 character of the mammalian fauna of the upper member of the 

 Cretaceous system, the Laramie, would without other evidence 

 lead to the conclusion that it was much older than it really is. 



Professor Fontaine makes the Potomac group about the geo- 

 logical equivalent of the Wealden of Europe, but for the rea- 

 son that it contains eighty known species of angiosperms out 

 of a total number of three hundred and seventy-five, I am in- 

 clined to regard it as newer rather than older than the Weal- 

 den. The fossil plants of the Jurassic have been collected in 

 large numbers and in many countries, but nowhere has a dico- 

 tyledonous plant been found in that formation, nor has an an- 

 giosperm been discovered in the Wealden of England or on 

 the continent of Europe. The plants of the Wealden have 

 been fully described by Drinker, Schenk and others, but all the 

 species known are cycads, conifers or ferns. I recently had an 

 opportunity, through the kindness of M. Dollo, of examining 

 the plants found with the Iguanodons at Bernissart, and among 

 them all there was not a trace of an angiosperm. This does 

 not absolutely prove that the Potomac group is of more modern 

 date than the Wealden, because the progress of plant life has 

 been, as we know, somewhat unlike in different parts of the 

 world, and the angiosperms may have begun their existence on 

 the Xorth American continent sooner than elsewhere, but it 

 seems hardly possible that eighty or more species of arborescent 

 angiosperms should have nourished on this continent before 

 they had put in an appearance in the vegetation of the Old 

 World. We may at least say that Professor Fontaine is fully 

 justified in his conclusion that the Potomac is not older than 

 the Wealden. 



The relations of the Potomac to the Amboy flora are of 

 special interest ; the two formations are consecutive members 

 of the Cretaceous system and the ''variegated marls" of Fon- 

 taine or the ''alternate sands and clays" of Uhler may be 

 regarded as the southern extension of the Amboy clay group. 

 Yet a long interval of time must have separated the epochs of 

 the two formations, since the floras are so entirely different. 

 Only a beginning has yet been made in the exploration of the 



