231 



b. Hydrographical Notes. 



Ill the tirst part of tliis work, a iiiiiiilicr of liydrojrrapliical 

 (lata from tlie tiords will 1)0 found. Now I will mention a fow 

 moiv dotail.-;. and treat of some tliiiiLjs wliicli have not yet been 

 mentioned. First then, some remarks on llir inlliienee which the 

 prcvailiiii.'' winds, waves and tidal currents exert mi veyetahle and 

 animal life in the sea. 



In a very iiiterestiii>; pajier. .Mr. !■'. W. IIakmkh has recently 

 explained tlie inipoitaiice of the prevailiiii; winds as a ireoloiiical 

 factor.') Mr. Hak.meu call.s attention to the fact that dead shells 

 are not found in lariie numbers on the eastern shores of the 

 counties of Norfolk and Suffolk, although there is no want of mol- 

 luscs in the adjacent sea. The reason for this absence of shells 

 is found by Mr. I!.\iiMi;ii in the fact that the prevailing winds at pre- 

 sent are westerly. On the contraiy, the presence of Crag beds on 

 the east coast presupposes a ditleient prevailing; wind from that 

 which is now the case. 



..Easterly gales might have been prevalent in that part of the 

 North Sea, rather than those from a westerly (juarter, as at pre- 

 sent.'' In another paper, Mr. Hakjier-) has drawn attention to 

 the tidal currents as a geological factoi'. 



He points to the state of things in the Irish Sea, „where an 

 accumulation of dead shells on the Turbot bank, ott' the coast of 

 Antrim, is caused by the tidal currents which sweep with much 

 velocity through the narrow channel separating Ireland from Scot- 

 land." The fact that in some places in Coralline Crag, layers of 

 large shells may occur, while at other places smaller shells are 

 predominant, is considered in the light of tidal currents, for Mr. 

 Harmer says : — „Shells are sorted out by currents of varying 

 strength as pebbles in beds of gravel ; small specimens Avould there- 

 fore have accumulated in one place, larger ones in another, and 

 comminuted shells, or fine calcareous sand in a third.'' 



Wind and current are not of little importance in dynamical 

 geology, on account of their carrying powei-. But just this charac- 

 teristic causes these factors also to have an influence, in different 

 ways, upon living creatui-es. The course of a current offers par- 

 ticularly favourable conditions for the nourishment of plankton- 

 eaters, and a current-facies of animals may be spoken of. It is 

 true that animal life is not profuse where the deposits of material 

 are greatest, but, on the whole, it is correct to say that the bed of 

 a current is profusely supplied with animal life. 



In a purely theoretical light, the supply of plankton for a given 

 animal must be in proportion to the velocity of the current. It is, 

 at any rate, evident that the motions of the water are of great 

 importance in connection with the supply of nourishment for plank- 

 ton-eaters. 



Dr. Ei)WAin> 1'>ri)wnf. •') has drawn attention to the fact that 

 medusae, which are kept in an aquarium where the water is un- 

 disturbed, will at tirst swim quickly about, „but in a few hours, it 

 sinks to the bottom, apparently tii-ed out. After an interval of 

 rest, it takes another swim, and again sinks to the bottom. This 

 is repeated until the medusa becomes exhausted; then it stays at 

 the bottom and slowly dies." This unfortunate state of things has 



^) Influence of Winds upon Climati' ilurii 

 Journ. Geol. Soc, vol. LVII, 1901, p. 408. 



-) A Sketch of the later tertiaiy Hist or 

 Assoc, vol. XVII, 1902, p. 42.o. 



^) On Keeping Jlednsaf : live in an Aipia 

 N. S. Vol. V, no. 2. 1898. 



the Plcistotene Epoch Quart, 

 of Kast Anglia. Proc. Geol. 

 in. .lonrn. Mar. Biol. Assoc, 



been remedied by Ur. E. T. Brownk and Dr. E. 1. Aliæn ha\1ng 

 succeeded in constructing an apparatus by means of whidi the 

 movements of the water have been skilfully imitated. Mr. Danne- 

 vifi's hatching apparatus is constructed on a similar principle. 

 With regard to the force of the tidal currents, it will easily be 

 seen that this will tlepend upon thi' height of the title, i. e. the 

 difference between ebb and flow. In the north of Norway, this 

 difference is, on an average, about 2 mtrs., and as a consequenct; 

 of this, the tidal currents are considerably strong in the narrow 

 channels and in the smallest parts of the fiords. Based upon 

 material furnished by the Norwegian „Gradmaalingskommission",') 

 I will give some figures which show tiie average difference between 

 high and low tide in succession in 1884 and 1885. 



1884. 188.5. 



Stavanger 0.424 m. 0.427 m. 



Bergen 0.988 „ 0.97.5 „ 



Kabelvaag 2.(i40 „ 2.014 „ 



Vardø 2.19;-) „ 2.175 „ 



Generally speaking, it may be said that the tidal wave runs 

 northwards along the coast, and the tidal currents flow- into the 

 fiords when the tide rises and outwards when it falls. 



In the channels of the „skjærgaard", it may be taken as a 

 general rule, that the direction of the current is northerly or 

 easterly when the tide I'ises, westeriy or southeriy when it falls. 

 But it must be remarked that in many channels the direction of 

 the current changes a little after the water has been at its highest 

 and lowest. In the currents running between the islands of Lofoten 

 (Gimsøstrøm, Napstrom, Sundstrøm etc.) the water at first flows 

 northwards when the sea is at half-high-tide and turns again at 

 half-low-tide. The same is said to be the case in the currents 

 which connect the Skjerstad and Salten Fiords. The best known 

 of these is the socalled ..Saltstrøm", which surpasses even „Mosken- 

 strømmen" in force. 



I have attempted, in an article on the two mael streams in 

 Norway, (de to store malstrømme i Norge) -) to explain the change 

 in the direction of currents at half-high and half-low-tide, and have 

 theoretically worked out the following conclusion: — If the inner 

 part of a fiord be connected by a current with the prmcipal fiord, 

 and the direction of this current be changed aftei' high and low 

 tide, the difference between ebb and flow will be less inside than 

 outside the said current. 



Thus, the difference between the niveau at high and low ^\-ater 

 should be less in the Skjerstad than in Salten Fiord. I have not 

 as yet had an opportunity of verifying this theoretical conclusion. 



Concerning the direction of the surface stream along the coast 

 of Norway, Mohn's current map is very instructive.') The fol- 

 lowing amusing little story shows that there, in the summer, may 

 be an easterly current along the coasts of Finmarken. Sophis 

 Tromholt'') relates that in the beginning of the eighties S/S. 

 «Nordstjernen" was in the summer wrecked on Knivskjælodden, a 

 little west of the North Cape, and very soon sank. A couple of 

 months later, the vicar of Næsseby had rowed out a little way in 



1) C'f. Vantlstandsmaalinger, h. 



2) „Naturen" 1901, p. 30r,. 



•■<) The X..rth Ocean, jil. XLIII. 

 *) Under Nordlysets Stra.aler, p. 



V, p. 124. 



Copenhagen 1885 



