342 The American Naturalist. [April, 
by high uplifts, usually far inland. The coast-line of the 
ocean was therefore, so far as may be determined up to the 
present time, a generally low area, where vast stretches of sands 
or mud-flats were shifted about by the surf and by the inflow- 
ing waters of tributary streams. It is these sandy beaches 
_and mud-flats that persist to-day as the Cretaceous rocks, bear- 
ing their countless imprints of archaic plants. 
Considering next, for a moment, the character of the plant 
remains from the Cretaceous, we find that in the Lower Creta- 
ceous, as studied by Fontaine, there are numerous ancient fern © 
and cycadean types. These become less prominent in the Upper 
Cretaceous, so that in 1874, when, under the researches of 
Heer and Lesquereaux, already 130 species were described 
from the Dakota group, of these only five are ferns or crypto- 
gamous plants, one doubtfully cycadean, six coniferous, two 
monocotyledonous, and the rest Dicotyledons—principally in 
the Archichlamydez, with only a very few ( Bicornes, Legu- 
minosæ, Ebenacex, ete.) referable’io the Metachlamydexe. The 
presence of the older types of cycads, conifers and ferns is 
important to be noted, for it is possible that the sole reason for 
their not appearing in countless numbers is the fact that they 
were cut off from the sandy-beaches and mud-flats by a thin 
but well-nigh continuous tension-line group of new and strug- 
gling Metasperme. 
The study of shore-lines of modern seas is essential to the 
further working out of the hypothesis in process of develop- 
ment in this paper. The writer is not aware that observations 
have been made with the considerations in view that would 
make them useful either for support or objection. His own 
studies of sea-shore areas are confined to the observation of 
Cape Cod, Massachusetts, during a single month. While there 
he found that the older plants are more numerous in the inner 
regions, and the newer more numerous nearer the coast. The 
_ coast-line then seems to be a tension-area. While there are 
many pines on the Cape, these, so far as I could discover, were 
generally distributed inland, reaching the border of the sea 
only on high promontories, and on low lands being generally 
separated from it by strips of herbage, tov shrubbery and hard- 
pS oe se 
