ENCROACHMENTS OF THE SEA. 585 
growth of aquatic plants, belonging both to fresh and to salt 
water, especially Zostera marina. This vegetation totally 
disappeared after the irruption, and, in some instances, was 
buried by the sand; and here again we have a familiar phe- 
nomenon often observed in ancient strata—the indication of 
a given formation by a particular vegetable species—and when 
the strata deposited at the time of the breach shall be accessi- 
ble by upheaval, the period of eruption will be marked by a 
stratum of Zostera, and probably by impressions of fresh-water 
fishes. 
“It is very remarkable that the Zostera marina, a sea-plant, 
was destroyed even where no sand was deposited. This was 
probably in consequence of the sudden change from brackish to 
salt water. . . It is well established that the Liimfjord 
communicated with the German Ocean at some former period. 
To that era belong the deep beds of oyster shells and Cardium 
edule, which are still found at the bottom of the fjord. And 
now, after an interval of centuries, during which the lagoon 
contained no salt-water shell fish, it again produces great num- 
bers of Dytilus edulis. Could we obtain a deep section of the 
bottom, we should find beds of Ostrea edulis and Cardiwm 
edule, then a layer of Zostera marina with fresh-water fish, 
and then a bed of Mytilus edulis. If, in course of time, the 
new channel should be closed, the brooks would fill the lagoon 
again with fresh water; fresh-water fish and shell fish would 
reappear, and thus we should have a repeated alternation 
of organic inhabitants of the sea and of the waters of the 
land. 
“These events have been accompanied with but a com- 
paratively insignificant change of land surface, while the for- 
mations in the bed of this inland sea have been totally revo- 
lutionized in character.” * 
* FORCHHAMMER, Greognostische Studien am Meeres-Ufer, LEONHARD und 
Buronn, Jahrbuch, 1841, pp. 11, 13. 
