FLUUA Ul" OLDKK I'UTO.MAC l-( JU.MA TION. :!G7 



It is not stningo that Mr. Knowlton (huls Ciipi-cssinoxyloii, for T fiiul at least 

 six ahmuiaiit and widely dilfuscd species ol' Se(|uiiia. determined, witiiont taking 

 tiie cones into consideration. I think it liiiiiily pr<il)ahle tiuit tiie i^^enera Sequoia. 

 .Vthrotaxopsis, and S])ii<'nole|)i(nuni liad wood closely alike, and that the trees j;re\v 

 ill forests and furnished most of the vast (piaiility of lijinite that- occurs in the 

 Pt)toinae. 



After Profe.s.s(jr l^'oiilaiiir liad h'ft \\'asliini;loii it occtiri-cd to Pto- 

 fessor Marsh that a papor on the flora of tlic Potomac forin;il ion ami its 

 o;oolo<iical significance oufjlit to be presen1c<l to the Xational Academy 

 of Scien(;es at its April meeting' in \\'ashington, and, as president of 

 the acatlemy, he invited me to present it. I assured him that Professor 

 I'^ontaine was the proper person to do this, and I made every effort to 

 induce him to do so, l)ut he declined on several grounds, and the duly 

 devolved on me. He authorized me to make any use 1 tliotiglit hest of 

 his mantiscript, which was then in my liands, and it was from this that 

 most of the facts tised by me were drawn. 1 could do this the better, 

 as, at Professor Fontaine's reciuest, I had prepared the three tables of 

 distril:)tition which form the concltuling part of the ptiblished monograph. 

 P'rom the data thtis l)efore me I prepared the paper which I read before 

 the National Academy of Sciences on April 20, 1888." 



Professor Marsh in describing the vertebrate remains had expressed 

 himself so emphatically on the Jurassic affinities of the fauna that it 

 was natural that I shotild incjuire particularly into the question whether 

 the flora could l)e regarded as confirming, or as not distinctly negativing, 

 that view. The dicotyledons presented the chief obstacle, this stibclass 

 never having thus far been found below the Urgonian, and only one species 

 as earl\' as this. But the Cretaceous dicotyledons thus far known are fuil>' 

 developed, often l:)elonging to genera still living, and it was clear to me 

 that this proved an extensive t^reak in the record. It was this f)oint 

 that I strove chiefly to bring out in this paper, and after ftiUy discussing 

 it I gave my conclusions in the following form : 



On numeroiLs occasions, dating as far hack as 1S7S, T liave express(>d the opinion 

 that the dicotyledons could not have liad tiieir origin later than the middle Jura, 

 and it will not surprise me if the final verdii't of science shall place the Polioniac 

 formation, at least the lower member in whicli the plants occur, within tliat geologic 



« Evidence of the fossil plants as to the ageof thePotomao formation: .\m..Ioui'n. .'^(■i.,3(lsei-.,Vol. XXXVI, 

 August, 1S8S, pp. 119-131. 



