588 TIMOTHY WILLIAM STANTON 
studied the stratigraphy and the flora of the Potomac in great 
detail, retains under that name all the strata originally included 
in it, and also makes it comprise all the beds that have been 
named the Raritan formation, extending from Maryland across 
Delaware and New Jersey to the islands off the southern coast 
of New England. That is, he makes it coextensive with Dr. 
White’s? non-marine division of the Cretaceous of the Atlantic 
border region which was believed to consist of two distinct 
formations, separated by a time interval that marked the dis- 
tinction between Lower and Upper Cretaceous. Though assign- 
ing these beds all to a single formation Professor Ward recog- 
’ 
nizes in it six distinct ‘‘series,’’ as follows: 
(6. Albirupean [in part equivalent to Raritan |. 
| 5. Iron Ore, 
: 4. Aquia Creek, 
Powsomumeye . Mount Vernon, 
w 
| 2. Rappahannock, 
L 1. James River. 
Each of these divisions, excepting No. 5, is, according to the 
author cited, characterized by a distinct florula altogether consti- 
tuting a flora of from 800 to 1000 species. Detailed discussions 
and comparisons of this flora are contained in the articles above 
referred to in the fifteenth and sixteenth annual reports of the 
U.S. Geol. Survey. From these it appears that while the whole 
formation is referred to the Lower Cretaceous the flora of the 
lower beds, in which the earliest known dicotyledons appear, has 
Jurassic affinities, and is related tothe Wealden flora. There is a 
progressive change, the modern types predominating more and 
more until in the uppermost beds (No. 6) the plants show a 
marked affinity to the Upper Cretaceous Cenomanian flora. An 
interesting comparison of the Potomac flora with the Lower Cre- 
taceous flora of Portugal, shows that while they have but few 
species in common the general characters of the two floras are 
very similar, and as Professor Ward remarks, ‘‘the lower Creta- 
ceous flora of Portugal is, botanically speaking, a very close repe- 
tition of that of America.’ This fact is in interesting agreement 
t Bull. U. S. Geol. Surv., No. 82, pp. 74-100. 
