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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 illustration of this is just at hand. A single dicotyledonous leaf was some time ago described,[1] under the name of Sterculia Drakei, from the upper sandstone of the Tucumcari beds near Big Tucumcari Mountain, New Mexico. This plant has lately[2] been referred to as the only dicotyledon known from the Trinity beds of the Comanche series, a reference that is, so far as we 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 Snowii, 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 sufficient 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 paleontological 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.[4] 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-

  1. ↑ Geol. Survey of Texas, 3d Ann. Rept., 1891, p. 210.
  2. ↑ Am. Geol., Vol. XII., 1893, p. 327.
  3. ↑ Proc. U. S. National Museum, Vol. XVI., 1893, p. 261-282.
  4. ↑ Op. cit., p. 281.
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