On the Erratic Phenomena of Scandinavia. 241 



rhombic porphyry of Von Buch, and also on all the acclivities 

 which surround the Tyrifjord, &c. There we no longer see 

 striae which are unequal and undulating, which cross one 

 another, and anastomose with one another, and which are 

 constantly becoming effaced ; but we there find lines which 

 are straight, simple, deeply graved, exactly parallel with each 

 other, and which continue for a considerable distance, that is 

 to say, for two or three yards, without being interrupted, and 

 without changing their direction, just as though the rock had 

 been acted on by a gigantic plane having unequal projections. 

 The margins of the fissures which traverse the rock are per- 

 fectly sharp ; the siliceous porous nodules are cut in two like 

 the knots of a plank of wood which has undergone the process 

 of planing ; the compact nodules, on the contrary, having 

 reacted on the planing surface, form a projection, and give 

 rise to a prolonged elevation in a straight line, which becomes 

 only gradually flattened, a circumstance proving evidently 

 that the hollow produced by the nodule in the planing-agent 

 has been retained for some time after it has passed the latter. 

 All these details are seen in a magnificent specimen of rhombic 

 porphyry, which I detached from an eminence behind Modum, 

 and which was much admired by Von Buch, to whom I shewed 

 it at Christian ia. 



It is evident, that if the striae were produced by currents of 

 water, the edges of the fissures, of which some at least must 

 have existed at the epoch when the grooving agent passed, 

 would be blunted, as well as the edges w^hich surround the 

 hollows of the porous nodules, and that the solid nodules 

 would not have had prominences following them ; the striae 

 likewise would not have been straight and parallel for con- 

 siderable distances. The grooving and polishing mass has 

 advanced with a firm step, without being deranged by any 

 obstacle, exercising its action in a uniform and very exact 

 manner, and leaving traces which admit of no doubt as to its 

 nature. 



The mountains of the Tyrifjord are not the only ones in 

 Scandinavia where I have observed the erratic phenomenon, 

 and where I have found convincing proofs against the h\'po- 

 thesis which attributes the striae to currents of water. I have 



