Variation of the Magnetic Needle. 323 



Arctic Sea, Professor Forchhammer may be cited. He says — 

 " The Gulf of Bothnia has been connected with the White 

 Sea, where, in the neighbourhood of Uleburg, a considerable 

 depression towards its shores may be observed, a complete 

 water communication existing from the White Sea through 

 the Gulf of Bothnia and the northern parts of the Ost Sea to 

 the Cattegat ;" and adds in a note, that between the Gulf 

 of Bothnia and the White Sea, " a communication by water 

 was kept up in the time of flood, even so lately as at the 

 commencement of the last century.'' 1 



Some effects may be attributed to the elevation of land 

 now going on, which, together with increased cultivation and 

 drainage, must tend to an elevation of temperature even at 

 the present time. 



In submitting these theories to the consideration of this 

 Society, I am aware that I can only support them by proba- 

 bilities ; but as the change of temperature in Europe, and 

 the variation of the needle are subjects on which no theories 

 have been adopted, I have some hope that the opinions I 

 have advanced may be thought worthy of farther considera- 

 tion. 



The Paragenetic Relations of Minerals. * 



The natural association of mineral species has long 

 attracted attention, and although since the time of Werner 

 it has been made the basis upon which distinctions between 

 rocks are established, still the subject has not been investi- 

 gated so fully as it would appear to deserve. Minerals 

 which occur together are enumerated in the description of 

 one or other of them, but no adequate account is given of 

 the mode of association, and their relations of date are even 

 still less regarded. 



Professor Breithaupt has for several years especially 



1 * Die Paragenesis der Mineralien. Mineralogisch, geognostisch und cheraisch 

 beleuchtet mit besonderer Riicksicht auf Bergbau. Von A. Breithaupt. 

 Freiberg, 1849. 



