256 The American Geologist. October, i89S 
our fossil flora into three great classes of cryptophytes, gy^mnosperms, 
and angiosperms, the sequence of their appearance and periods of 
maximum development would be in the same order. The percentages, 
of these classes in any floras should therefore be a fair indication of 
the relative ages of the floras. A typical Jurassic flora, such as that 
of Siberia, contains, roughly, the following percentages: cryptophytes-, 
22; gymnosperms, 74; and angiosperms (?), 4. The older Potomac 
flora, which is regarded as lower Cretaceous, contains the same classes 
in the percentage of 39, 39, and 22; the newer Potomac, regarded as 
Middle Cretaceous, 8. 13, and 79; the Amboy clays, 6, 13, and 81; 
the Dakota group, i, 5, and 94. Similar examples, of percentages 
were also calculated for other floras regarded as Cretaceous in age. 
The main fact, which is at once seen, is the manner in which the per- 
centages of the gymnosperms and angiosperms are reversed. Few 
angiosperms, and only those of a doubtful character, have been found 
in any formation recognized as Jurassic; so that when it was ascer- 
tained that in the Amboy Clay flc^-a and its , equivalents the angio- 
sperms represent from 70 to 90 per cent, of the entire flora, there 
was little hesitation in considering it as well advanced in the Creta- 
ceous period. There would be nothing inconsistent in regarding the 
lowest of the older Potomac strata as Jurassic, but even there it would 
require definite paleontologic evidence, while in regard to the Amboy 
Clay series it is safe to say that a Jurassic fauna will never be found 
in connection with its flora. 
• In face of the direct evidence of the fossil flora, therefore, it would 
seem a very hazardous undertaking, without ample evidence in re- 
buttal, to draw the line of separation between the Jurassic and Creta- 
ceous so that in the west the base of the Cretaceous would be rep- 
resented by the Dakota group and in the east by the clay marls of the 
Mat?.wan formation. (The paper was illustrated by tables of per- 
centages and charts.) 
6. Some Feldspars in Serpentine, Southeastern Pennsylvania. By 
Prof. T. C. Hopkins, State College, Pa. Feldspar occurs in this 
district as dikes or veinlike masses in serpentine, sometimes attaining 
a thickness or width of 20 to 25 feet. The most extensive area is in 
Chester county, extending also into Lancaster county; but there is 
another area in central Chester county, near the corundum mines. 
The feldspar is snow-white to pink in color, and seems to be wholly 
orthoclase. Some of the dikes have been exploited to a depth of 
60 feet. 
7. The Region of the Causses in Southern France. By Rev. 
Horace C. Hovey, Newburyport, Mass. Lofty tablelands in the 
departments of Lot and Lozere, along the western declivity of the 
Cevennes mountains, are known as the Region of the Causses. The 
term "Causse" is derived from the Latin word calx, meaning lime- 
stone. Some of the finest roads in Europe run along the plateaus, 
and occasionally descend into the valleys. But the author's explora- 
