344 MKsozoic FLORAS OF l'mtf:d statf:s. 



many pliKcs In hods of sand coiitamiuf^ woody lilicr replaced by siliceous lualter, 

 for in all cases where wood is enveloped bj' clay, wliicli admits with difficulty the 

 percolation of water, the mass is found in a lilack, charred state: but, on tlie con- 

 traiy, when deposited in a matrix which admits the infiltration of water, such as 

 sand, soil, or loam, the wood appears in the v( plaful or pflv'ifud state. 



Dr. EdwaiTl Hitchcock, in hi.s early report, published in 1833, had 

 of course only to deal with the northern extension of the Potomac forma- 

 tion, which contains none of the older beds, but he was aware of the great 

 extent of this formation, as evidenced l)y the following remark: 



The patches of this formation that have been described in Massachu.setts are 

 doubtless only the remnants of a vast extent of these strata, extendinn; at least from 

 Cajjc Cod to the Ijorder.s of the Gulf of Mexico, and how far eastward, where the 

 Atlantic now rolls, we can form no proliable ojnnion, though there is .some reason for 

 supposing that they once even reached Europe, along whose shores similar strata are 

 found at present." 



Messrs. Clemson and Taylor commenced their extended investiga- 

 tions into the geology and mineral resources of Virginia at about this 

 time and pul)lished their first papers in 1835. * Mr. Clemson concludes 

 his paper with a fairly full description of the Potomac beds in the vicinity 

 of Fredericksburg, including that of "Alum Rock," a mile south of that 

 place. He also refers to the lignites and fossil wood found in that region, 

 and speaks of "a blue argillaceous bed six inches to a foot in thickness, 

 which divides easily and displays to view fine impressions of plants" 

 (pp. 312-313). This appears to be the earliest mention of plant impres- 

 sions in the Older Potomac formation, and may allude to the same locality 

 where Professors Uhler and Fontaine later obtained so large an amount 

 of material of this class. 



Mr. Taylor, in the paj^er' that immediately follows this, devotes six 

 pages (320-325) and one folded plate (pi. xix) to the description and 

 illustration of the plants from this locality. He states that his "attention 

 was first directed to these plants by Mr. F. Shepherd, who at our request 



« Report on the Geology, Mineralogy, Botany, and Zoology of Massachusetts, by Edward Hitchcock, 

 Amherst, 1833, pp. 201-202. 



* Notice of a geological examination of the country between Fredericksburg and Winchester, in Virginia, 

 including the gold region, by Thomas G. Clem.son: Trans. Geol. Soc. Penna,, Vol. I, Pt. II, Philadelphia, 183.5, 

 pp. 298-313, pi. xvii. 



'■ Review of geological phenoniciia, mid ihc deductions derivable therefrom, in two hundred and fifty miles 

 of sections in parts of Virginia and Maryland; also notice of certain fossil acotyledonous plants in the Secondary 

 strata of Fredericksburg, by Richard C. Taylor: Ibid., pp. 314-.32.5, pis. xviii-.xi.x. 



