46 The American Geologist. January, 1892 
In fact it makes a comparison of the forms determined with those 
of all the formations in which any of its species occur, In rea- 
soning with regard to it, therefore, one is constantly checked in 
considering any particular horizon, by the facts relating to the 
horizons both above and below. For example, in treating the 
Triassic flora in the numerical table last described, if one’s atten- 
tion were confined either to the Oolite or to the Lias, one might 
conclude that either of these formations was near to the one to be 
determined. But dropping the eye down the column to the Rhetie 
it is observed that a considerably larger percentage of the same 
species, both identical and related, occur in this. So great was 
this similarity that Professor Fontaine decided that this must 
represent the nearest approach in geologic age to the Richmond 
coalfield. But the subsequent researches of Stur, with which 
Professor Fontaine was, of course, unacquainted, in the Keuper 
formation of Lunz, in Austria, and in the Keuper floras of 
Europe of nearly the same age, especially those of Raibl in 
Carinthia, and of Neue Welt in Switzerland, have shown that the 
Keuper flora of Europe, although much less abundant, contains a 
larger number of American Triassic forms than does the Rhetic 
flora of Franconia, South Sweden, Brunswick, ete. So that al- 
though only a very few American forms occur at any horizon 
lower than these, nevertheless we seem compelled to conclude 
that this Upper Keuper horizon of Lunz, Austria, comes nearer 
to that of the American plant-bearing Triassic deposits than does 
any other in the world. 
Now the question may arise whether all this really proves any- 
thing. Where two floras as old as the Trias and as widely sepa- 
rated as Austria and Virginia are found to agree so remarkably 
in the forms they contain, is it legitimate to conclude that the age 
of the one was the same as that of the other? Certainly not. 
And yet, if facts like this do not prove that there existed an 
epoch on both sides of the Atlantic, which to all intents and pur- 
poses may be regarded as simultaneous, then all paleontologic 
data are without value. The fact to be borne in mind is that the 
correlation established by such data is homotactic and not neces- 
sarily chronologic. Reasons may exist why the same types may 
have come upon the stage at a later or earlier period at one of 
these localities than at the other. But of the nature of these 
retardations or advancements we are without scientific explana- 
