FLORA OF 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 antiquated. As will be seen 

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

 mine most of the forms. Mr. Taylor saw that these beds had nothing 

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

 stratigraphical position are somewhat important: 



As relates, therefore, to the evidence which these fossil plants furnish as to the 

 relative age of the formation wherein they are deposited, we are led to the conclu- 

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

 resemblance to any of the plants of the Richmond coal field that have come to our 

 knowledge, and decidedly bear the impress of a more modern character. 



In this view we are confirmed by the lignites and silicified wood in some of these 

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

 Alleghanies, for instance, and still further removed fi-om that of Richmond. 



The large broken masses of silicified wood are unquestionablj^ remains of vascu- 

 lares or dicotyledonous plants or trees, no member of which series has yet been 

 observed in our coal vegetation. They resemble in some respects 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 impalpable sand.'' The latter character pre- 

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

 crj^stals. 



Again we have other lignites which are broken up and abundantly intermixed 

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

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

 fibers preserved. 



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

 these deposits than those of the Richmond 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 observed 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, Murchison, 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 belemnites and other fossils of the has, 

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

 have seen no traces of algai, cycadese, or of conifera, all of wliich orders occur spar- 

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



