542 GEOLOGICAL MEMOIRS. 



the relative amount of the earlier and later elevations along the 

 coast, reducing the first or most ancient to 7 '6 m , making the 

 second or intermediate movement of 6'9 m , and leaving the third 

 or most recent 14*l m , and therefore considerably greater than the 

 other two. 



§ 3. Observations and Hypotheses concerning the Formation of 

 these Lines of ancient Level. 



Although the tendency of the waves to wear away the cliffs 

 against which they beat, and form a beach made up of these 

 materials, is a fact sufficiently well known, perhaps it has hardly 

 been considered with reference to its geological bearing, and in 

 relation to the ancient lines of level in certain districts. It is 

 also by no means easy to make out very satisfactorily the causes 

 which have determined the formation of those lines at one place 

 rather than another. 



Mr. Darwin, indeed, in his memoir on the parallel roads of Loch- 

 aber*,, has assigned the following causes as sufficient to account 

 for these differences ; namely, the greater or less degree of steep- 

 ness of the slope ; the nature of the rock ; the local circumstances 

 favourable to the production of vegetation on the bank, preserv- 

 ing it after the retreat of the waters ; and the configuration of the 

 neighbouring coast. 



First, of all let us distinguish between the terraces formed by 

 lines of erosion and of projection ; the first of which offer no 

 serious difficulties, since the terrace is manifestly a local pheno- 

 menon exhibited at the mouth of a river or stream of running 

 water, and one which ought to be present at the extremity of each 

 valley so provided. In most of the valleys in the district now 

 under discussion this terrace has been observed, and in the others 

 there is no positive proof of its absence ; and indeed it may occa- 

 sionally have been removed by the very circumstances connected 

 with the elevation. 



The exposure of a coast line to a beating surf tends more or 

 less to the formation of a line of erosion ; while, on the other hand, 

 direct exposure to the more violent effect of the waves during 

 tempests gives no such well-defined line : and it is doubtful 

 whether we could trace them where the exposure is greatest, 

 namely, on the northern side of the outermost border of islands 

 which fringe the coast of Finmark. 



The effect in these northern latitudes of the incessant dash of 

 short broken waves, not rolling in from a wide expanse of ocean, 

 seems to me however to correspond exactly with that presented by 

 the ancient lines of level ; in fact, we may observe in more than 

 one spot on the coast analogous lines now in the progress of form- 

 ation. Such, for example, appear at the promontory of Rastabynses, 

 where the sea has eaten out for itself a bank strictly resembling 

 that which exists at an elevation of 16 metres above its level, 



* Phil. Trans. 1839. p. 60. 



