FLORA OF OFDFIJ roiO^LVC FOK.\L\riOX. oil 



at Pi'ofessoi' I'oiUaine's roquost, from his inanuscrii)!, th(> first .i;iviii<>; the 

 localities in tho formation from which each species was collected: lh(> 

 second giving the distribution of all the species hitherto known from 

 other beds in all countries, and also of those species most closely allied 

 to Potomac forms; and the third showing tlu^ formations in their 

 ascending geological sequence from which Potomac sp(>cies and species 

 allied to them lunc becMi obtained. Professoi' I'onlaine discussed the 

 !ige and general character of the Potomac; flora in the concluding portion 

 of the work. He thinks that much of the confusion that exists relative 

 to age arises from the use of terms in different senses, and especially fi-om 

 that of the tern! Wealden. On this point he says: 



Ik'ioro till' cxaiuinutioii of tlio o'oological relations of tlic I'otoinar lloi'a is iiiiiliT- 

 lakcii it will !){' well to cU'finc in what sense the nanii's of (■ciiain m'olojrical forma- 

 tions, to wliich frccnient reference must be made, will i)e taken in this memoir. 

 The two formations which are eapat)le of misconception are the Wealden .-ind 

 Neocomian. By some the Wealden foi-mation is reij;arded as an inde])endeiil i:i-on|) 

 forminj,' tiie nppennost member of the Jurassic. Others regard it as a .series of i>eds 

 contemporaneons with a portion of the lower Neocomian, formed in estuari<>s and 

 marshes at the time w hen a j)ortion of the typical lower Neocomian, which is marine, 

 was being deposited- in the sea. The latter view is the one assumed in this memoir. 



In this work the Neocomian period is taken as including; the IJrgonian and 

 Aptian of l)'Orl)igny. the former being, when present, the middle member and the 

 latter the u])])er member of the formation. When, then, jcference is made to 

 Neocomian ])lants, fossils of the W'ealden, Frgonian, and Aptian groujis aic included 

 and not distinguished (.see pp. ;331~:3;^2). 



He then takes up the several classes, families, and genera, and con- 

 siders the bearing of each on the age of the beds. His final conclusion 

 is as follows: 



This being true, we should expect to find in any large collection of Neocomian 

 plants a great mingling of tyjies. We should find the survivors of the old floras 

 and the newly arrived precursoi's of the more recent ones mingled with a number 

 that attain their development in and are peculiar to the Neocomian. This is exactly 

 what we find to l)e true of tiie Potomac flora. That .so many of these plants are new 

 is perhaps to be explained, in part at least, by the fact already mentioned, that the 

 flora of this epoch is very poorly represented and comjjaratively but little known. 

 It is not possible to say positively to what precise e|)och of the Neocomian the 

 Potomac belongs. Its flora ranges from the Wealden through the Prgonian. and 

 probably includes some Cenomanian forms (see p. :]4S). 



Doctor Knowlton's bulletin, already mentioned, on the fossil wood 

 and lignites, appeared in advance of Professor Fontaine's work. Doctor 



