108 THE AMERICAN NATURALIST. [VoL. XXXVI. 
own feet, so to speak, by dissolving away the rock to which 
they ought to hold fast, they would be useless. 
Suppose, now, that a wave-cut terrace, which is being 
widened by the inroads of the sea, and which is swept by a 
littoral current bearing the shore-drift along with it, becomes 
overspread by a growth of coralline algz. Geike, in his Tert- 
Book of Geology, speaks of the preservation of shore rocks by 
the overgrowth of these corallines (“calcareous nullipores "'). 
These plants cover the substratum with a brittle, calcareous 
crust, which, though a considerable protection against the 
cutting of water-borne sand, is shattered by the blow of a 
pebble. This calcareous enameling retards, to some extent, 
the lowering of the terrace by the sand-bearing current. That 
is, while the terrace widens, the water above it may remain 
comparatively shallow. Moreover, many of these corallines, as 
Amphiroa and Corallina, produce, in addition to the calcareous 
crust, numerous erect, jointed fronds ; and the latter, as we have 
seen, offer the best possible lodging place for Phyllospadix. Here, 
then, we have the conditions most favorable to Phyllospadix, — 
shallow, but not quiet, water, and corallines to anchor the seeds. 
Gradually, if there is eelgrass within drifting distance, the 
terrace becomes dotted with green tufts, the tufts spread 
into patches, and ultimately the higher border of the terrace 
presents, at low tide, the appearance of a wind-laid hay-field, 
the “ grass,” one to two meters long, lying in prostrate tangles. 
Now begins the accumulation of debris. Stones and pebbles 
being carried alongshore by the current, odds and ends of 
seaweeds, and all the multifarious small drift of the shore, 
are caught in the network of rhizomes and wiry leaves. The 
larger stones may themselves serve as footholds upon which 
the rhizomes climb higher and wave their leaves higher in the 
water. Every stone entangled serves to stop more pebbles 
and sand, and, as the mass continues to pile up, the rhizomes 
are at last buried deep under it; but as long as the tips of 
the leaves wave free the plant thrives. On almost any of our 
beaches there may be found between tide-lines tufts of slender 
leaves apparently growing in the sand, but in reality anchored 
to the rock a meter, perhaps, below. 
