372 THE JOURNAL OF .GEOLOGY. 



460 species have been described from this formation, of which 

 number no less than 394 are peculiar, that is, have never yet 

 been found outside of it. A very large number of these plants 

 are so characteristic that their discovery in strata of unknown age 

 would settle at once their reference to this horizon. An illustra- 

 tion of this is just at hand. A single dicotyledonous leaf was 

 some time ago described,' under the name of Sterciilia Drakei, 

 from the upper sandstone of the Tucumcari beds near Big 

 Tucumcari Mountain, New Mexico. This plant has lately^ been 

 referred to as the only dicotyledon known from the Trinity beds 

 of the Comanche series, a reference that is, so far as ^Ye know, 

 highly improbable, for Fontaine, in his descriptions of all of the 

 plants now known from these beds 3 finds no trace of dicotyledons. 

 A glance at the figure of the Tucumcari plant suffices to show that it 

 is Sterculia S?wwii, a well-known, very abundant, and characteristic 

 plant of the Dakota group. This leaf, together with what is now 

 known of the position of the rocks containing it, is amply suffi- 

 cient to settle the age of this portion of the Tucumcari sandstone, 

 a conclusion agreeing perfectly with the results several times set 

 forth by Professor R. T. Hill from stratigraphic and paleonto- 

 logical .grounds. The Potomac formation furnishes a parallel 

 example. This series of beds, extending in almost unbroken 

 line from New Jersey to Alabama, contains a known flora of 737 

 species, over 80 per cent, of which are peculiar. 



An example of the complete accord existing between fossil 

 plants and other organic remains in determining age is offered by 

 the Trinity Division of the Comanche Series of Texas, the flora of 

 which, so far as known, has recently been worked out by Fontaine."* 

 The particular beds in this series, from which the plants came, have 

 been named the Glen Rose or alternating strata, by Professor 

 R. T. Hill, and their age determined by marine invertebrates, as 

 Neocomian or basal Cretaceous. The flora consists of twenty- 



'Geol. Survey of Texas, 3d Ann. Rept., 1891, p. 210. 

 ■^Am. Geol., Vol. XII., 1893, p. 327. 



3Proc. U. S. National Museum, Vol. XVI., 1893, P- 261-282. 

 Op. cit., p. 281. 



