130 (Review of ^RecenL Geological Literature. 
willow, oak and trees of modern tjpe as the predominant forms. Angio- 
sperms have supplanted gynmosperms, and the transition has had all the 
appearance of having been suddenly accomplished. The Potomac for- 
mation furnishes in part a history of the transition. Here we find a 
curious commingling of archaic and modern forms; and not only that 
but here are also species in which the ancient and modern types are 
mingled in the same individual. A modern external form may be com- 
bined with an old-fashioned internal structure. 
The modern student of geology has never doubted that the oaks, wil- 
lows, maples, poplars, etc., described by Lesquereux from the Dakota 
group, were not the earliest Angiosperms. They must have had their 
predecessors; and those predecessors, all would have agreed, must have 
been comprehensive types combining characters belonging to the older 
and the newer floras. The Potomac formation furnishes us a glimpse of 
some of these predecessors, with ancient and modern characteristics 
mingled and blended in precisely the manner we should have anticipated. 
The second formation which has been added by the investigations here 
recorded to the geological series is called the Appomattox formation. 
The beds of this formation are found at a number of localities, but their 
principal exposures are on and near the Appomattox river from its mouth 
to some miles west of Petersburg. It consists, in part at least, of orange 
colored sands and clays. In places it overlies directly the Potomac for- 
mation, but in some places it is seen above fossiliferous Eocene beds and 
in others it even overlies the Miocene. It is newer therefore than the 
Miocene, but its age has not been definitely settled. It has furnished no- 
fossils. 
The third of the formations here described is called the Columbia for- 
mation from the distinct in which it has been most carefully studied. This 
formation attains its greatest thickness along the river and thins out in 
the places between. The materials of the Columbia formation vary 
greatly, grading from fine silt to coarse sand, gravel, pebbles or bowlders 
up to a foot in diameter. In places the material is more or less perfectly 
stratified. The formation is newer than the Appomattox. Its fossils? 
consisting of the remains of the reindeer, elephant, mastodon, elk, etc 
would indicate that the formation belongs to the Quaternary. It belongs 
to the earlier rather than the later Quaternary, however, for it is found 
passing under glacial drift, and by the amount of erosion and degree of 
alteration in it, it is proved to be " much older than the terminal moraine 
or the drift sheet whose margin it marks." 
The deposits of the Cokmibia formation are all sub-estviarine and bear 
testimony to a submergence of the region in which they occur of at least 
150 feet. Coincident with the submergence was a long-continued de- 
pression of temperature. Indeed the deposits bear evidence of two 
epochs of cold that were separated from each other "by an interval three, 
five, or ten times as long as the post-glacial interval; that the earlier cold 
endured much the longer; that the earlier cold was the less intense and 
the resulting ice sheet stopped short (in the Atlantic slope) of the limit 
