_ FLORA <,)F OLDER POTOMAC FORMATION. 345 



furnished the Geological Society with specimens" (p. 321"). The seven 

 figures given on the plate are clear and show the true nature of the plants, 

 but the nomenclature employed is of course antitjuated. As will Ije seen 

 on page 373, Professor Fontaine was able from the figures to deter- 

 mine most of the forms. Mr. Taylor saw that these l)eds had nothing 

 to do with those of the Richmond coal field, and his remarks on their 

 stratigiaphical position are somewhat important: 



As relate.s, tliorefore, to the evidence which these fossil plants furnish as to the 

 relative age of tlit; formation wherein they are deposited, we iire led to tlie conclu- 

 sion that it is of secondary origin, perhaps coeval with the ooHtes. They have no 

 rescnihiaiict' to any of the phuifs of tlie Kiclunond r((a] field tiiat have come to oui- 

 knowiedgc, and decidedly Ix'ar tiie impress of a more modern ciiaracter. 



In tliis view we are confirmetl l)y tlie lignites ami silicified wooil in some of these 

 beds, whicli indicate a geological age much less remote than the coal fields of the 

 Alleghanies, for instance, and still further removed from that of Richmond. 



The large broken masses of silicified wood are unquestionably remains of vascu- 

 lares or dicotyledonous plants or ti'ees, no member of which series has yet been 

 observed in our coal vegetation. They resemble in some i-espects the silicified wood 

 of the Portland oolite of England, and like them exhibit no marks of perforation by 

 the Teredo. 



The silicified fragments found by Mr. Nuttall near the James River are described 

 as" penetrated with quartz of an opaque white color, destitute of the resinous fracture, 

 and easily crumbling into an almost impalpalde sand." The latter character ))re- 

 vails in the Fredericksburg lignites, and some of them are coated with small quartz 

 crj'stals. 



Again we have other lignites which are bn»ken up and abundantly intermixed 

 with the grits, and even in the finer argillaceous seams, wliicli fragments occur only 

 in the form of burnt or charred wood, not bituminous, but havmg their ligneous 

 fibers preserved. 



We have, moreover, a distinguishing evidence of tlie more recent character of 

 these deposits than those of the Kiclimond coal field, in the friable open texture of 

 the grits, which are no more crystalline than ordinary oolites, whereas the rocks of 

 Richmond are compact, frequently subcrystalline and porphyritic. 



It must be ol)served that all the genera to which we have assigned the fossil 

 plants of Fredericksburg occur in the oolitic group of Europe. For this fact we 

 have the testimony of M. A. Brongniart, Saussure, Phillips, Murcliison, De la Beche, 

 and many others. These genera have also been found, according to M. Elie de Beau- 

 mont, to a certain degree associated with l)elenuiites and other fossils of the lias, 

 inasmuch as those fossils are embedded both above and beneath them. But we 

 have seen no traces of algae, cycadese, or of conifera, all of which orders occur spar- 

 ingly in the oolitic series of Europe (pp. 324, .325). 



