INTRODUCTION. 3 



The distance apart of the most remote phint localities and the nnmber 

 of intervening spots affording specimens give reason to think that the fossils 

 obtained enable us to form a fair notion of the vegetation of that period. 

 This is especially fortunate, for the hitherto known flora of the oldest 

 Cretaceous is exceedingly scanty. 



One feature of the Potomac flora at once attracts attention. This is 

 the large number of plants confined to single localities. In many cases 

 this number is so great as to give the local floras a peculiar facies, which, 

 were it not for the connecting links, would induce one to believe that they 

 difter considerably in age. This localization is perhaps chiefly due to diff"er- 

 ences in the conditions attending the entombment and preservation of the 

 plants. At any rate this feature attests the richness of the flora. The 

 variety within certain limits and the abundance of the vegetation nmst 

 have been great. 



The distance from Deep Bottom on James River to AVhite House 

 Blufl" on the Potomac is more than JIO mile.s. If we include the Maryland 

 localities, 50 miles nmst be added. The number and location of the inter- 

 vening stations will appear in the account of them presently to be given. 



When fossils have been collected at given localities it may easily happen 

 that natural or artificial changes so alter the exposures that the spot yielding 

 the impressions is soon concealed. The Potomac beds, owing to their want 

 of coherence and the poverty of exposures in them, are especially liable to 

 have fossiliferous portions hidden. Then, too, plant-impressions occur in 

 them Avith exceeding irregularity, at best sparingly, and in very thin layers. 

 It seems, then, desirable to describe with some minuteness the spots where 

 plant-fossils were found. 



Before beginning these descriptions it is proper to give some account 

 of what was formerly known of plant-fossils from this formation. The 

 belief, before referred to, in the Triassic age of the strata now in question 

 was due in part to the apparent absence of all fossils that could throw light 

 on the subject and call for a separation of the Potomac from the older 

 Mesozoic. So far as is known to me, only two persons have published any- 

 thing concerning the occurrence of fossil plants in the Potomac beds of 

 Viro'iuia. 



