File:The Quarterly journal of the Geological Society of London (13206182474).jpg

274 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. .April 14,
where expand into dense conformable masses, nor form amygdaloids
nor trap tuffs. Hence they are easily overlooked in a cursory sur-
vey, although in reality very numerous, and often persistent for great
distances.
On the Geological Age of the Coal-Fields of Eastern Virginia^ as
determined by Fossil Remains.
I shall now consider the chronological relation of the coal-field, in
determining which we have no direct evidence from superposition.
The only other strata occupying a similar position in the hypogene
region on the Atlantic Slope, with the exception of some of a similar
character near Raleigh in North Carolina, are those commonly called
the new red sandstone of Massachussets, Connecticut, and New Jer-
sey. In part of New Jersey the strata of that red sandstone are un-
conformable to a part of the palseozoic series of the Appalachian
system, and are therefore subsequent in origin to the movements
which gave to the old carboniferous and other still more ancient
groups of the Alleghany mountains, their present strike, dip, and
flexures. The red sandstone therefore being posterior in date to the
Appalachian coal strata, the next question is, whether the coal-field
near Richmond is of the same age as the red sandstone, or of newer or
older date ? The difficulty of replying to the inquiry consists in this :
that most of the fossils of the so-called new red sandstone are fish, or
the foot-tracks of birds, without any plants, while those of the coal
near Richmond are almost exclusively confined to plants, so that we
have scarcely as yet any satisfactory terms of comparison in the same
family of organic beings common to the two. Before alluding to the
plants, I shall say something of the small number of shells and
ichthyolites which I met with in the coal-field near Richmond.
Shells of the Coal-Field.
Fig. 6.
In the carbonaceous shales associated with the main seam, and
usually not far above, a great number of minute flattened bivalves are
often observed in some places, as at Harden' s pits, north of Black-
heath (see «, fig. 6) . They resemble Cyclas in outline ; they are thin