IIO THE AMERICAN NATURALIST. . [Vot XXXIII. 
were alternately covered with the tides and exposed to the at- 
mosphere. The rocks are mostly conglomerates, sandstones, 
and shales, evidently shore or shallow water deposits, often 
ripple-marked or sun-cracked, and occasionally bearing the 
footprints of land animals or amphibians which wandered over 
them. 
The vegetation of the period is but sparsely represented in 
the collections which have been made in New Jersey, but these 
probably fairly represent its general characters. Dr. J. S. New- 
berry has described about ten species from the state,! of which 
three are pteridophytes, and the remainder probably all refer- 
able to the gymnosperms. One living genus (Equisetum) is 
recognized. 
Thus far, in any collection of Triassic plants which has been 
made, nothing higher in development than the monocotyledons 
is even indicated, and we may regard the Triassic flora as one 
composed almost wholly of ferns, cycads, and conifers, with 
cycads as the dominant type. 
Towards the close of the Triassic period great physical 
changes occurred, of which the extrusion of trap dikes was one 
of the most prominent features. The indications also are that 
that portion of the continent now represented by New Jersey 
and vicinity was raised above its former level and remained so 
for a long time, while farther south it was depressed, as in this 
state we know of no deposits which can be even provisionally 
referred to the next succeeding period, the Jurassic, which, how- 
ever, occur in Maryland and southward. In New Jersey, there- 
fore, we havea break at this period in the geologic sequence, and 
in consequence a hiatus in the line of plant development which 
has been at least partially bridged by Prof. Wm. M. Fontaine 
and Dr. Lester F. Ward in their studies of the Potomac flora 
of Maryland and Virginia.? The exact geologic age of the 
lower strata of this formation has not been definitely settled, 
1 Fossil Fishes and Fossil Plants of the Triassic Rocks of New Jersey and the 
ee Valley, Monographs of the United States Geological Survey, vol. xiv. 
2 Fontaine, Wm. M. The Potomac or ey See Flora, Monographs 
of ed United States Geological Survey, vol. xv, pts. : 
ard, L. The Potomac Formation, Fi Saar gost Report of the United 
phd Geological Survey, pp. 307-397. 
