W. M. Fontaine—Mesozoic Strata of Virginia. 37 
The direction, in which the lateral thrust operated in this 
field, was from east to west, and it seems not yet to be 
exhausted, for this region is often affected by minor earth- 
quakes, and at intervals of ten or fifteen years, by very pow- 
erful ones, the last occurring a few years ago. The shocks 
pass from east to west. It is probable that the gradual depres- 
sion of the coast is connected with this westward thrust. 
fossil Plants.—So far as known to me, the only plants from 
_ this field which have been published and described, are those 
_ made known by Rogers and Bunbury. Both of these authors 
considered the plants to be of the age of the lower Oolite of 
England. Most geologists, however, seem to agree in consid- 
_ ering the beds yielding the plants, to be of the age of the 
_ Keuper, or Upper Trias. It must be borne in mind that only 
_ the lower, or coal-bearing portion, bas yielded these plants. 
. Among European authors, Heer and Schimper are the only 
_ ones who, so far as I know, express an opinion concerning the 
_ age of the beds, based on an examination of the plants. I have 
not seen Heer’s remarks, and hence do not know on. what 
grounds he concludes that the plants are Triassic. Schimper, 
on page 277, vol. i, of his Pal. Veg., founds his belief in the 
Triassic age of the beds yielding the plants, both on the ani- 
mal and plant life. I will consider only the latter. 
e says, in speaking of the characteristic Equisetum of this 
field, which he calls Hguisetum Rogersii, that it is nearer to E, 
arenaceum, the characteristic Equisetum of the Trias, than to &. 
columnare, the plant of the Lower Oolite with which Rogers and 
_ Bunbury thought it to be identical. He, however, only saw a 
_ cast of the interior of the Richmond plant. He says, farther, 
_ that this coal field has Pterophylla and Ferns, which have most 
_ affinity with the characteristic species of the Keuper. It does 
not appear from what source he derived this impression. 
_ He is mistaken both concerning the Equisetum, and the 
_ other plants from this field. This Equisetum is next to Macro- 
_ temopteris grandifolia, the most abundant and widely diffused 
_ plant of the field. I have beautifully preserved specimens, on 
1 field, while he refers its constant companion, the Equiestum 
: above mentioned, to the Keuper of the Richmond field. The 
