FLUKA OF OLDER I'O'JOMAC FOKMAllON. 843 



This shows that the freestone qiiai'i'ios on and near the Rappahannock 

 Kivof had lonfj; been worked at that lime. The other paper, pul)hshed 

 ten years later," is devoted to '"the freestone (luariies on the Potomac 

 and Rappahannoc, from the former of which th(» fi-eestone employed in 

 the public buildings of tlie United States at Washington is obtained" 

 (p. 284). He gives a good description of the freestone rock, including 

 that of the clay nodules so characteristic of it. On ])age 2S7 he says: 



11 ("/(/, IVdin trunks and hranclit's of trees ol' lurjie size lo small twiijs, either 

 entirely carhonated or the wood (•arl)onated and the hark in a hhroiis state, so as to 

 have tile appearance of a net, and a (dnsitleral)ie (i(><:;ree of tenacity: or the hark 

 fihrous and the wood in a state quite triahie; or the wood replaced hy pyrites which 

 efHoresce in the air; or in cavities the sitles of which have the impression of branches 

 in minute lamification and are lined with a pellucid crust, ]irohal)iy calcareous spar. 

 This latter evidence of the admixture of wood is to l>e found < hielly near i^'redericks- 

 hurg. 



On July 15, 1823, Mr. John Finch read a paper l)ef()re the Academy 

 of Natural Sciences of Philadelphia'' in whicli he classed all the Ijeds of 

 the coastal plain as Tertiary and compared them with those of Europe. 

 On page 39 of this paper he says: "At Washington, under the mass of 

 diluvial! gravel of which the higher part of the Capitol hill is composed, 

 there is a stratum of clay which contains many organic remains. Trunks 

 and branches of trees are found at a distance of fifty-four feet from the 

 surface." It is probable that these remains were in the Potomac forma- 

 tion, although they may have been in the overlying Columbia formation, 

 in which such objects have been found within the city of Washington. 



In 1829 Messrs. Morton and Vanuxem published a paper of a very 

 general character,'" but their "Secondary formation" evidently- iircludes 

 the whole of the Potomac formation and also the marls of New Jersey. 

 In the following statement they exactly describe the conditions under 

 which the wood and lignite of the Potomac formation occur: 



In many of the States there is a bed of clay (No. 2 of tiie diagiam) containing 

 ligniii or clmnrd wood, with pyrites, amber, etc., which is no doiiht rc])i-esented in 



" An uccouiit of the freestone quarries on the PdUmmc and IJiippahinniDi- rivns, by B. II. Latn)l)e: Trans. 

 Alii. Pliil. Soc, Vol. VI, Pt. 11, 1S()9, pp. 2S3-29;{. 



'' Cieological essay on tlio Tertiary formations in .Vincrica. Iiv .lohn Finch: \u\. .lourn. Sei., original series, 

 Vol. VII, 1824, pp. .31-43. 



c Geological ohservations on the Secondary, Tertiary, and alluvial formations of tlie Atlantic coast of the 

 United States of America, arranged from the notes of Lardner Vauu.xem, by S. G. Morton, M. V>.: Journ. .Vcad. 

 Nat. Sci. Philadelphia, Vol. VI. Pi. 1. 1S2!I. pp. .^.9-71. 



