FLORA OF OLDER POTOMAC FORMATION. 347 



the description occupying the remainder of the section clearly relates to 

 the Potomac beds. 



In his paper "On the Age of the Coal Rocks of Eastern Virginia,"" 

 devoted chiefly to the older of these formations, he refers to the younger 

 beds as follows: 



The coarser rocks, lying above the carbonaceous strata, and forming the greater 

 part of the thickness of the series, contain very few organic remains, and those in so 

 imperfect a condition as to have Uttle or no value for purposes of comparison. 

 There are, however, strong reasons for behevmg that these strata, by a gradual 

 transition, pass upward into the series of felspathic sandstones, described in my 

 report of the Geological Survey of Virginia for 1840, under the title of Upper Second- 

 ary Strata. The latter, considered by Messrs. Taylor and Clemson, as ' 'of secondary 

 origin, perhaps coeval with the Oolites," have since been referred hj myself and Prof. 

 H. D. Rogers to the upper part of the Oolite series, so that this great division of the 

 geological column, though still perhaps very imperfectly represented in the United 

 States, comprises a thickness of considerably more than one thousand feet of strata 

 (seep. 301). 



Mr. Richard C. Taylor, in his work on the Statistics of Coal, published 

 in 1848, returns to this subject ^ in the treatment of the coals of Virginia. 

 Relative to the lignites, silicified wood, and fossil plants he says : 



In 1834 the Geological Society of Pennsylvania published in their fii-st volume 

 a paper communicated by the author of this work on the lignites of the secondary hori- 

 zontal strata of Fredericksburg, accompanied by six lithographed figures of plants. 

 These lignites are in no place in sufficient abundance to constitute a seam or bed, 

 much less a workable bed, but as interesting specimens of silicified masses of wood 

 and fragments even of large trees, which reminded us of those of the Portland rock 

 of the south of England ; besides an infinite number of impressions and carbonized 

 remains of more delicate varieties of plants, that are not undeserving of a passing 

 notice. 



On looking over the imperfectly defined series of tliese plants, it will be seen 

 that they are all cryptogamous, cellulares, or acotyledones, with the exception of 

 Thuytes, and that they belong to genera some of whose species are distributed 

 abundantly amongst the coal vegetation of all parts of the world. These species, 

 however, appear to be new — that is, they do not belong to the Carboniferous period. 

 One approaches to the Oolite period, and the consideration given to this group of 

 plants led to the conclusion that they were "perhaps coeval with the Oolites." 



« Trans. Assoc. Am. Geol. and Nat., Boston meeting, 1842, Philadelphia, 1843, pp. 298-301. 

 '' Page .54. Second edition, revised and brought down to 1854 by S. S. Haldeman, Philadelphia, 18.55, 

 p. 299. 



