42 The American Geologist. January, 1392 
is very different these figures might lead to an erroneous im- 
pression. What it is desired to learn is the relative preponder- 
ance in any florule of species common to other florules. This can 
only be shown by a table of percentages. For the Triassic basins 
of the United States I present this information in the following 
form: 
Commontoand 
Basins or Areas. | Occurring in | Confined to— some other Per cent. in 
5 basin other basins. 
Connecticut Valiey 23 13 i) 39 
New Jersey and } | 18 5 13 792 
Pennsylvania. § 
Wate seen ss: 56 34 22 39 
North Carolina.... a2 25 27 52 
New Mexico and } 1B 1 9 15 
Arizona. ..... ) * 
Considering the well known fact that in almost any new local- 
ity for fossil plants, the majority of the forms found will be new 
to science, the percentages of common species here shown, with 
the exception of the western basin, are large and may fairly be 
taken to prove actual or approximate contemporaneity of de- 
position. 
The next step is to ascertain how many of the species have 
been found at other localities and horizons. This is what I have 
denominated their fore‘gn distribution. To show this a table is 
prepared with columns for such different foreign localities, ar- 
ranged in ascending geological order, the lines of which are oc- 
cupied by the species found in the locality to be compared. The 
species that have been already described from other localities and 
horizons are then indicated in the proper column by some char- 
acteristic mark. The range or geologic history of each species is 
thus recorded upon the same line on which the species is written. 
Such a detailed table of distribution of the species of any 
given group, is exceedingly simple and elementary; and in so far 
as it goesrequires no explanation. But there are other considera- 
tions to be taken intothe account. Inall the lower forms, consist- 
ing chiefly of cryptogams, cycads, and conifers, two facts are to 
be considered: In the first place it is to be remembered that our 
knowledge of the nature of these ancient forms is not sufficient 
for us to predicate with certainty their generic relationships. They 
are usually extinct forms and are given names accordingly as ex- 
tinct genera. In the second place, as all paleontologists now 
know, the ancient forms of life on the globe were less definite, or 
