54(3 MESOZOIC FLORAS OF UNITED STATES. 



National Museum. The third was made by Mr. Bibbins for the Maryland 

 Geological Survey in July, 1897. It is somewhat smaller than the one 

 last mentioned. 



The exact locality at which all these collections were made is the 

 Mount Pleasant mine, near the foot of the hill called Tip Top that lies 

 between Deep Run and Stony Run and overlooks the Patapsco Valley 

 above Elkridge Landing. The mine is in a ravine, now thickly wooded, 

 on the south or Stony Run side of Tip Top, and not far from that stream, 

 west of a well-known spring. The mine has been long abandoned, and 

 there is a pile of ferruginous rocks that were taken out of the old shaft. 

 The original specimen coUected by Mr. Bibbins in 1890, and the whole of 

 the collection made by Mr. Bibbins and Professor Ward on August 31, 

 1896, were obtained by breaking up a single one of these rocks, which was 

 the only one seen at that time in which plant impressions occurred. 



The three collections taken together yielded the following species: 



Athrotaxopsis expansa Font. ? 4 specimens. 



Athrotaxopsis grandis Font. « 1 specimen. 



Athrotaxopsis tenuicaulis Font. 1 1 specimen. 



Sphenolepidiimi dentifolimn Font. ? 2 specimens. 



Sphenolepidium Sternbergianum densifolium Font 16 specimens. 



Sphenolepidium Sternbergianum densifolium Fontaine." 

 PI. CXV, Fig. 1. 



Imprints of this species occur on most of the specimens from Tip Top. 

 The one first obtained by Mr. Bibbins in 1890 (M. G. S., No. 8871) 

 bears them, as well as those of Athrotaxopsis expansa ? The specimen 

 figured on PL CXV, Fig. 1, was collected by Professor Ward and Mr. 

 Bibbins on August 31, 1896. Its counterparts, showing the impression 

 quite as well, was collected by Mr. Bibbins in July, 1897, and bears the 

 number: M. G. S., 8283. Besides the ones already mentioned, the 

 collections contain 14 others, making 16 altogether. 



This collection is too small and imperfect to give the evidence from 

 the plants much value in fixing the precise age, especially when the only 

 fossil that is positively determined ranges from the base to the top of the 

 Lower Potomac of Virginia. So far as the evidence goes, it indicates 

 that the age of the strata is Arundel or Rappahannock. 



a See p. .507. 



