6 THE POTOMAC OR YOUNGER MESOZOIC FLORA. 



take, in the absence of the professor, all these specimens were sent to the 

 World's Exposition at New Orleans. Nothing has been heard of them 

 since. As the material was very fragile, and probably was badly packed, 

 it was no doubt ground to powder before reaching its destination. 



It is much to be regretted that these impressions were lost before they 

 had been carefully, studied and described. My recollection of them is not 

 very distinct, but it is sufficient to enable me to say that the Baltimore fos- 

 sils were chiefly rather delicately incised ferns, with a sphenopterid facies, 

 not unlike the most important plants collected by Meek. 



The plants found by Professor Uhler at Fredericksburg contained cer- 

 tain portions of some species that I have never been able to find myself. I 

 especially remember an impression of the summit of a large leaf, which then 

 seemed to me to be a Macrotcemopteris. From my own discoveries since, I 

 am now sure that it was the tip of a large Ammozamites. I have never suc- 

 ceeded in finding a single specimen showing the termination of the leaves of 

 this plant. As Professor Uhler was kind enough to offer to place these spec- 

 imens in my hands for description, I looked forward with much pleasure to 

 their examination. The cases above mentioned embrace, so far as I know, 

 all tlie discoveries of fossil plants hitherto made in the Potomac formation. 



When I first began to search for fossils in the Potomac beds I knew 

 of no discoveries of plant-impressions in them except those mentioned by 

 Professor Rogers. Judging from the lithology and the stratigraphy of 

 these beds, I was convinced that Professor Rogers was right in supposing 

 that they differed in age from most of the Mesozoic of Virginia. His men- 

 tion of the existence of plants in the formation induced me to undertake a 

 systematic search for plant localities. In the course of my first reconnais- 

 sance I paid a visit to Baltimore, and having learned from Professor Uhler 

 of the existence of Tyson's cycad trunks and of his own collections 

 obtained at Baltimore, I made with him a hasty examination of these fos- 

 sils at the Museum of the Maryland Academy of Sciences. 



Professor Uhler had not told me of his discovery of plant-impressions 

 at Fredericksburg, but while at the museum my attention was attracted 

 by a small collection of fossil plants unlike any that I had ever seen. Pro- 

 fessor Uhler informed me that he had collected them at Fredericksburg, and 



