508 MESOZOIC FLORAS OF UNITED STATES. 



This furnishes the largest number of specimens, 19 in all. Some of 

 them are beautifully preserved. PI. CXII, Fig. 1, gives one of these 

 distinct forms. This fossil belongs to both the Rappahannock and the 

 Aquia Creek horizons, being most common in the latter. The specimen 

 figured is No. 8452 of the Maryland Survey, and its counterpart is No. 

 8444. 



FOSSIL PLANTS FROM THK MOUTH OF HELL HOLE. 



[PI. LXXX, No. 147.] 



Another spot in the same vicinity is called "Mouth of Hell Hole." 

 On the same day Mr. Bibbins collected here the following plants: 



Baieropsis foliosa Font. ? 4 specimens. 



Celastrophyllum obovatum Font. ? 1 specimen. 



Sphenolepidium Sternbergianum densifolium Font 4 specimens. 



All the species found at the Mouth of Hell Hole are also found at 

 the principal locality with a larger number of specimens, so that they do 

 not indicate a different horizon. 



The plants found at these two localities do not make it entirely clear 

 whether they belong to the Mount Vernon or the Aquia Creek horizon. 

 It is true that there is a considerable proportion of the plants occurring 

 on the Rappahannock horizon found here, but they appear rather to be 

 survivors than dominant forms. Some, such as the Sequoia f inferna, 

 the Aristolochicephyllum crassinerve, the dicotyledons of modern aspect, 

 Baieropsis foliosa, etc., have never been found as low as the Rappahan- 

 nock horizon. On the other hand, forms of Sapindopsis, which are so 

 abundant on the Aquia Creek horizon and are so characteristic of it, are 

 wanting. Again, most of the forms, like Populus, etc., so characteristic 

 of the Mount Vernon strata, are equally wanting. 



As stated before, most of the rock matrix containing these fossils is 

 a light or grayish chocolate material. This contains the older elements 

 of the flora and may he Mount Vernon in age. But some of the rock 

 material is a light-gray, arenaceous shale, exactly like the Aquia Creek 

 strata at the 72d Milepost. This contains all the younger elements of 

 the flora and may be Aquia Creek in age. The labels accompanying the 

 fossils do not state whether or not all of them come from the same stratum. 

 Professor Ward's collections at the original Mount Vernon locality show 



