74 Notices of Memoirs — The Terraces of Norway. 



This the author showed was not tenable, as the strongest Nord- 

 hausen sulphuric acid fails to dissolve aluminous shales and Silurian 

 slates ; and also that any such acid secretion would act more readily 

 on the valves themselves. From many experiments on the cutting 

 of hard siliceous substances, the aiithor found that the softer the 

 substance was in which the cutting material was impacted, the 

 greater the amount of the work done. He was thus led to the con- 

 clusion that the Pholadidse bore with the strong muscular foot alone, 

 and that they obtain the minute particles of silica from the waves 

 or the arenaceous rocks in which they are found ; and hence there 

 is no necessity for either an acid or silicious secretion. That the 

 foot was the boring apparatus, and not the valves, he proved from 

 a specimen of a Pholas-hole in shale, where the pedal depression of 

 the animal was distinctly seen. 



He also exhibited a piece of glass bored to the depth of 1"50 of 

 an inch, by means of the point of the finger and emery alone. 



III. — The Terraces of Norway. — By Prof. Kjerulf, of Christiania, 



[Translated from the Norsk, by Marshall Hall, Esq. Eeprinted from " Scientific 

 Opinion" of Feb. 23, March 2, and March 9, 1870,] 



THE terrace-like steps, which it is the object of this paper to 

 describe, are remarkable features of the Norwegian valleys. 

 These valleys are filled with various deposits of clay, sand, and 

 gravel, but the floor of each valley does not slope evenly from its 

 commencement to the lower end of the valley, where it opens into 

 the sea, but it rises thence by steps, from lower to higher plains, 

 irrespective of the river which traverses it along an inclined plane. 

 These steps, the surfaces of which are apparently horizontal, have a 

 gentle slope at the upper portion, and usually terminate below in a 

 steep slope of about 30°. These are the Terraces. 



It seems most reasonable to suppose (says the author) that these 

 valley terraces were caused by a water-surface on a level with them. 

 If the sea be the agent, marine remains ought to occur from the 

 highest terrace far up the valley to the lowest, at the present sea- 

 shore, and at the same time a certain uniformity might be expected 

 in the nature of the materials filling up the valley. But marine 

 remains are only to be found at the lower altitudes, under 500 to 

 600 feet. At about the same altitude the nature of the bottom of 

 the valley is evidently different. From 500 to 600 feet is, therefore, 

 the highest beach-mark, and it will be presumed that steps found 

 lower than this are marks of the sea-level, whilst for the other steps 

 higher up some different cause must be assigned. 



With respect to their situation, the steps may be classed into two 

 large groups : (1) Those that occur in a completely open situation ; 

 (2) Those comparatively closed in, and partially supported by the 

 damming produced by the mountains on both sides approaching each 

 other. 



The maritime steps proper are all open. The inland steps are 

 almost all distinctly closed. 



