The Liimfjord

The irruption of the sea into the fresh-water lagoon of Liimfjord in Jutland, in 1825—one of the most remarkable encroachments of the ocean in modern times—is expressly ascribed to "mismanagement of the dunes" on the narrow neck of land which separated the fjord from the North Sea. At earlier periods, the sea had swept across the isthmus, and even burst through it, but the channel had been filled up again, sometimes by artificial means, sometimes by the operation of natural causes, and on all these occasions effects were produced very similar to those resulting from the formation of the new channel in 1825, which still remains open. Within comparatively recent historical ages, the Liimfjord has thus been several times alternately filled with fresh and with salt water, and man has produced, by neglecting the dunes, or at least might have prevented by maintaining them, changes identical with those which are usually ascribed to the action of great geological causes, and sometimes supposed to have required vast periods of time for their accomplishment.

"This breach," says Forchhammer, "which converted the Liimfjord into a sound, and the northern part of Jutland into an island, occasioned remarkable changes. The first and most striking phenomenon was the sudden destruction of almost all the fresh-water fish previously inhabiting this lagoon, which was famous for its abundant fisheries. Millions of fresh-water fish were thrown on shore, partly dead and partly dying, and were carted off by the people. A few only survived, and still frequent the shores at the mouth of the brooks. The eel, however, has gradually accommodated itself to the change of circumstances, and is found in all parts of the fjord, while to all other fresh-water fish, the salt water of the ocean seems to have been fatal. It is more than probable that the sand washed in by the irruption covers, in many places, a layer of dead fish, and has thus prepared the way for a petrified stratum similar to those observed in so many older formations.

"As it seems to be a law of nature that animals whose life is suddenly extinguished while yet in full vigor, are the most likely to be preserved by petrification, we find here one of the conditions favorable to the formation of such a petrified stratum. The bottom of the Liimfjord was covered with a vigorous 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 phenomenon 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 accessible 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 numbers of Mytilus edulis. Could we obtain a deep section of the bottom, we should find beds of Ostrea edulis and Cardium 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 comparatively insignificant change of land surface, while the formations in the bed of this inland sea have been totally revolutionized in character."