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 

 and compressed, have a horny texture, oval and inequilateral, with a 



