546 GEOLOGICAL MEMOIRS. 



ence to this subject are left for the special consideration of M. 

 Siljestrom.* 



In order to arrive at an explanation of these phenomena which 

 shall be at once uniform and precise, the expressions ancient level 

 of the sea, elevation, elevator y force, have been introduced in this 

 memoir, but without any idea of prejudging the question, and merely 

 because such language is common among geologists. Although 

 a complete examination of the many different ways of explaining 

 these phenomena does not at all enter into my plan, I shall offer 

 some, remarks on the different hypotheses as I briefly enumerate 

 them. 



It is clear in the first place that the great difference of level 

 between the extreme points of our line of elevation, renders it 

 quite impossible to explain the existence of these lines by the 

 fracturing of the barrier of some ancient lake ; and I cannot but 

 suggest that an accurate geodesic levelling should be applied in 

 the case of the doubtful lines in Scotland, for this would at once 

 determine the possibility of such an explanation being correct. 



Some authors have remarked, that a simple alteration in the 

 arrangement of the masses in the interior of the earth, might, by 

 changing the direction of it's weight over a greater or less extent 

 of surface, depress or elevate the level of the water, and as a con- 

 sequence of the displacement of the vertical change even the hori- 

 zontality of ancient lines of level. Theoretically this may be true, 

 but if we consider the two series of numbers given abovef , it 

 will be seen that such an explanation fails entirely, for while one 

 series (that relating to the most recent elevation) may appear to 

 harmonise with the theory, the other exhibits far too rapid a dimi- 

 nution in the passage from the last term but one to the last. 



If it be assumed that the terraces and lines of erosion may be 

 due to powerful currents setting in from the valleys in the in- 

 terior towards the North Sea across the fjords and the sounds, it 

 will be necessary to explain, 1st, the presence of marine organic 

 remains ; 2. the reason why the lines of level do not gradually 

 but sensibly rise towards the extremities of the valleys affected by 

 the increase of the slope suddenly bringing the banks of the streams 

 under this local influence ; and, 3. whence was derived the enormous 

 rush of water necessary to cover, for a considerable time, not only 

 the valleys and fjords of Finmark, but also, doubtless, the whole of 

 the Norwegian coast. 



Polished rocks, as well as erratic blocks like those of Scandinavia, 

 are found also in Switzerland, and it has been supposed, M. Agassiz 

 having formally stated his concurrence with the view, that they 

 had a common origin. According to this view, glaciers on a far 

 grander scale than those which exist at present, once occupied all 

 the valleys, and by their progressive downward movement produced 

 all these appearances. Such an hypothesis may, indeed, account for 

 the erratic blocks and polished and striated rocks of these countries ; 



* One of M. Bravais' coadjutors in this commission. — Ed. 

 \ See ante, p. 541 . 



