FORCHHAMMER ON THE BOULDER FORMATION. 377 



rocks which are naked near the coast gradually, as we advance 

 inland, becoming clothed with vegetation, the number of loose 

 fragments of rock increasing and the proportion of scratches upon 

 them diminishing in about the same ratio. I am of opinion that 

 these phenomena bear some relation to one another, for if the 

 flood had lasted but for a short time, it would not have carried 

 away the stones or left such traces of its action upon the rocks. 

 I think, therefore, we may conclude that the rate of elevation was 

 more rapid formerly in Scandinavia than in later times. 



We must now consider whence were derived the numerous 

 erratic blocks deposited in the boulder formation, since the action 

 of water is sufficient to account both for the inclined and vertical 

 face of the rock, although it in no way explains the scratches, 

 except they were produced by the mere advance of hard heavy 

 bodies, such as fragments of rock pushed on by water. 



If we consider the way in which waves break upon a shore, we 

 shall perceive that the crown of the wave falls over, and that the 

 whole strength of the wave is, so to speak, concentred in the upper 

 part of it * : the principal materials driven forward by the waves, 

 however, do not consist of fragments broken off by this violent 

 beating upon the parent rock, but rather of vast masses of detritus, 

 which still remains in the interior of Sweden, where neither 

 scratched nor furrowed rocks occur, and the masses of which are 

 in all probability partly the result of some early and violent dis- 

 turbance, assisted perhaps by more recent disruptions an<^ earth- 

 quakes, as in the neighbourhood of Gothenborg, aided no doubt 

 partly by the splitting and transporting power of frost. 



Some peculiarities of the scratched rocks, however, yet remain 

 to be explained, and among the first of these is the fact that the 

 broad furrows are also scratched, since it would seem that greater 

 pressure was required for the finer scratches than one could obtain 

 with the smaller stones. It is also difficult to understand the 

 parallelism of deep and fine scratches upon a rock, since even if the 

 differences in the direction of the waves as compared with the 

 main direction is as nothing in the case of the larger and heavier 

 stones, this cannot be the case also with the smaller ones ; but I 

 think all these difficulties vanish when we consider that the time 

 of the occurrence of storms is generally winter, that the waves 

 beaten against and broken by a resisting object, and frozen by the 

 cold, become mixed up into a mass with broken fragments of rock, 

 and that the icy crust thus formed of ice and gravel together pro- 

 duces a much greater effect than could be otherwise obtained. To 



* As an instance of this might be quoted the case of the dykes on the west 

 coast of Schleswig and Holstein, where injury is rarely done from without 

 except when the waves wash over and carry away the lining of hard clay, and I 

 have myself seen in the Faroe islands a large fragment of basaltic dolerite which 

 the inhabitants informed me had been broken off from the solid rock by the 

 action of the waves in winter, and lifted up upon the higher ground. If this 

 part of the rock had been a ledge or shelf like those already described, the 

 waves would have gradually driven this fragment forward. 



