GEOLOGICAL HISTORY OF THE VIRGINIA COASTAL PLAIN. 213 



coast. The shore-line during the Upper Cretaceous evidently lay farther to 

 the east in Virginia than it had during the Potomac period. As has been 

 stated before, the Upper Cretaceous deposits do not outcrop in Virginia but 

 have been penetrated by the deep-well borings at Fairport and in the 

 vicinity of Norfolk. 



Eocene history. — In early Tertiary time a depression carried most of 

 the region again beneath the waters of the ocean and the Eocene deposits 

 were formed. The great amount of glauconite present in these formations 

 indicates that the adjacent landmass must have been low and flat so that 

 the streams carried only small amounts of terrigenous materials. The 

 water in which these were deposited was doubtless not deep, as glauconite 

 is not known to be produced at great depths. The land-derived material at 

 the beginning of the Eocene consisted of coarse sand and occasionally small, 

 well-rounded pebbles. Later the material brought in by the streams was 

 much finer and consisted of fine sand or clay. Many forms of animal life 

 characteristic of the infralittoral zone existed in these waters and their 

 remains are now found composing layers of marl frequently many feet in 

 thickness. 



Studies of the fossils found in the Eocene deposits indicate that there 

 were many changes in the fauna during this time. These changes were 

 probably influenced to a greater or less extent by variations in the physical 

 environment, yet the character of the deposits themselves gives little 

 evidence of such changes. Instead, it seems probable that the conditions 

 under which the Eocene deposits were produced were remarkably uniform, 

 considering the great length of time which elapsed from the beginning to 

 the close of the period. 



Miocene history. — Eocene sedimentation was brought to a close by an 

 uplift in which the shore-line was carried far to the eastward, and probably 

 all of the present State of Virginia became land. This was followed by 

 submergence, and another cycle was begun. The deposits of the Calvert 

 were now laid down upon the eroded land surface of the jSTanjemoy. Slug- 

 gish streams carried in fine sand and mud which they gave to the waves and 

 ocean currents to spread over the sea bottom. The shore-line in the northern 

 part of the Coastal Plain of Virginia was not quite as far west as it had 

 been during the Eocene submergence. In the central and southern portions, 

 however, it was farther west than it had been at any previous time since 

 the beginning of Coastal Plain deposition. Thus we find in northern Vir- 

 ginia the Calvert beds resting upon the Nanjemoy, in the James Biver basin 

 upon the Aquia, while somewhat farther to the south they are found in im- 



