t4 Th e AA merican Geologist. January, 1892 
or allied species. But this introduces a new element into the 
table since it is manifestly impossible to indicate these relation- 
ships by the same means which were used to indicate identity. 
It is necessary to use a separate line for each of these related 
species; also to use an additional column at the left hand of the 
margin in which to write their names. It is then possible to use 
the same sign for the related species as was used for identical 
species, and to carry out its geological distribution in the col- 
umns as above described. 
Such a table is useful when one wishes to follow out any one 
particular species, and to‘trace its distribution to other localities 
and horizons. But it does not give a comprehensive view of the 
relationships of the flora in general; the data which it contains 
require to be condensed into more convenient form. 
The first step in such condensation should probably be the ar- 
rangement of all the species in the ascending geological order, 
of the formations in which they also occur. It is instructive in 
such a table to show the indentical and the related species for 
each formation separately; that is to say, all the species together 
which are found at the lowest, next lowest, third lowest forma- 
tion, etc., of the entire range of the group. In this way those 
horizons at which the largest number of species occur are clearly 
g } ) 
brought into view, not only by the number of species which 
occur in them, but also by the relative number of those which 
are identical to those which are merely allied. 
This condensation may be still further generalized by the re- 
duction of the list of species to the numerical form; that is, by a 
statement of the number occurring at each horizon without 
enumerating the species at length. Just as in the table last men- 
tioned the same species will often be several times repeated, so in 
the table now under consideration,* the numbers in the columns 
include such over-lappings. | Hitherto we have considered the sub-- 
ject only from the geological standpoint, but it is of interest to 
geology as well as to botany that some classification be made of 
the principal types of vegetation embraced in any flora. As the 
table last described is very short it is possible to introduce some 
such classification in it. In discussion the Triassic flora, which has. 
*This table appears in the Bulletin of the Geological Society of America, 
Vol. iii, p. 29. The larger tables used to illustrate this paper will be 
published in my essay on correlation, in preparation. 
