20 



Tliese ineasurcnients have been earried out in tlio surface of the water, 

 but where tlie depths ave so incousiderable as iu the Limfjord there is no 

 very great difference in temperature and sahnity above and below. We see 

 the eonsiderable changes of temperature according to the season, from 

 0,2 — ]8,,i" C, while the temperature at the bottom of the deep Seandinavian 

 fjords is 6 — 8 - C. all the year round. The salinity reaches its maxinium in 

 summer, but there is no slight difference between the two years, botli with 

 respect to salinity and temperature. — 



As the Limfjord is a very peculiar water, the like of which will seareely 

 be found at raauy piaces iu Europe, 1 shall give some information of it, iu 

 order to make it easier for the foreign reader to understand the peculiarities 

 of this remarkable fjord. This is so much the more necessary as the foreign 

 literature seems to attacli some importance to the uuderstandiug of the condi- 

 tions under which the plaice lives in the Limfjord, and, among others, the 

 well-knowu P^nglish maritime biologist E. W. L. Holt has done me the honour 

 of making this matter the subject of a close investigation in > Journ. Mar. Biol. 

 Assoc«, vol. V. 1897, pp. 82—88. 



»As it is well known«, says J. Collin in his 'Limfjordens marine Fauna 

 188-4', »the part of the Limfjord which is west of Løgstør might till the year 

 1825 be said to consist chiefly of a complex of larger and smaller fresh-water 

 lakes, which were in connection with one another and had their joint outlet 

 into the Cattegat through the long, proportionally narrow arm of the sea be- 

 tween Løgstør and Hals, the water of which according to circumstauces entered 

 with different force.« 



It was in 1825 that the great irruption of the North Sea took place and 

 changed the salinity, fauna, and flora of the fjord, so that the old fresh-water 

 and brackish water fauna was driven into the narrowest creeks, and a salt-water 

 fauna immigrated from the North Sea: oysters, lobsters, plaice, etc. 



The mouth of the fjord by the North Sea (at Thyborøn) is at the nar- 

 rowest place only a few hundred yards broad, and is, where it is deepest, c. 

 3 — 4fathoms: inside, on the »fjord-shallow«, as well as outside, onthe »sea-bar«, 

 the passage is broader, but also much shallower, c. 8 — U feet. On account of 

 the »wauderings« of the sand; tlie depths change very much; and in order 

 to keep a fairway for the vessels, it is necessary indeed, every year artificially 

 to dig up the sand at the fjord-shallow by means of a sand pumpingsliip. At 

 the eastern mouth, by the Cattegat, they keep (artiticially also) a depth of c. 

 18 feet, but at several piaces in the narrow eastern part of the fjord, the depth 

 is at the deepest only 6- — 10 feet. Tiie depth in tlie great western expansions 



