L. F. WARD — PLANTS OF THE AMERICAN TRIAS. 31 



Keeping this botanical classification in view, we may next look at this flora from 

 the point of view of its geological importance, that is, of ascertaining how many of 

 these forms have any diagnostic value for geology. To determine this we need to 

 know the number of forms that are not confined to the American Trias but are 

 found in other formations and at other localities — forms that have a geological and 

 geographical distribution. The table shows that only 40 of these forms have such 

 a distribution, viz, 17 ferns, 4 equiseta, 1 rhizocarp, 13 cycads, and 5 conifers. But 

 there is another class which has also a diagnostic value, viz, those species which, 

 having no distribution of their own, are clearly shown to be allied or related closely 

 to other plants occurring in other formations and localities. Of these there are 17, 

 viz, 7 ferns, 2 equiseta, 7 cycads, and 1 conifer. Putting these two elements together, 

 we have 57 diagnostic species, viz, 24 ferns, 6 equiseta, 1 rhizocarp, 20 cycads, and (i 

 conifers. This leaves 62 species, or over 52 per cent, not found in any other forma- 

 tion and not allied to any species known elsewhere ; therefore without diagnostic 

 value. 



GENERAL CONCLUSIONS FROM FOREIGN DISTRIBUTION. 



It will be seen that tables three to six, inclusive, relate to the foreign dis- 

 tribution of the fifty-seven diagnostic species, and it may now be inquired in general 

 terms what is the final outcome of these extended comparisons. Do they serve in 

 any sense to correlate the American Trias with any of the Old World deposits ? If 

 the answer is that they do not enable us to say with positive certainty that the 

 American deposits are exactly parallel with any others, this is a very different thing 

 from saying that the facts thus presented are worthless, or that they do not greatly 

 increase our knowledge of the position which they occupy in the geological scale. 



It must be remembered that it is chiefly from the plants that we derive this 

 knowledge. All discussions of the animal remains, even the abundant ichnites of 

 the Connecticut valley, left their age enshrouded in doubt. Plarly mistakes in de- 

 termining the vegetable remains caused opinion to fluctuate all the way from the 

 Oolite to the Carboniferous. The present accurate knowledge fixes the horizon 

 with almost absolute certainty at the summit of the Triassic system, and narrows 

 the discussion down chiefly to the mere verbal question whether it shall be called 

 Rhetic or Keuper. At present, as we saw in the detailed consideration of the facts 

 brought out by the fourth table, the beds that seem to be most nearly identical, so 

 far as the plants are concerned, are those of Lunz, in Austria, and of Xeue Welt, 

 near Basle, in Switzerland. These have been placed by the best European geolo- 

 gists in the upper Keuper. Our American Trias can scarcely be lower than this, am 1 

 it probably cannot be higher than the Rhetic beds of Bavaria. 



In the discussion following the reading of the paper, Mr. G. K. Gilbert 

 remarked that the four eastern provinces are more closely related by 

 their floras than any one of them is related to the one western province, 

 and that the same conclusions were reached by a consideration of the 

 purely physical features of these provinces. 



The author of the paper said that the species of the American Trias 



have more affinities with the meager flora of the European Keuper than 

 with the much more abundant flora of the Rhetic. 



