184<6.] MURCHISON ON THE SCANDINAVIAN DRIFT. 367- 



are nearly covered with wood (the exception in this denuded tract), 

 the northern face only being entirely free from vegetation, since no 

 shrub or plant can there find root in the smoothed spherical and 

 polished surface of a crystalline rock where it is void of vertical fis- 

 sures. 



In Wassunde parish, which we crossed in making a lateral excur- 

 sion to the north-western arm of the Malar Lake, the gneiss and 

 the hard granite veins in it are beautifully exposed, the striae tra- 

 versing them in this case from S. 15° E. to S. 15° W. This is the 

 direction which Sefstrcim believed to prevail in Sweden, but my own 

 observations would lead me to think that the markings in many 

 other districts are as often from the west as from the east of north. 



Since I am now treating of a tract abounding in isolated hum- 

 mocks or promontories of rock, the direction of each of which trends 

 on the whole from north to south, I will here mention a fact which 

 seems to have escaped former observers, viz. that not merely is the 

 northern end of each hillock worn and abraded, or in Alpine lan- 

 guage, '• moutonne^ but also to a certain extent the east and west 

 sides of each, — its southern face alone remaining in a natural and 

 unaltered state. But in the amount of degradation and polish, and 

 above all in the striation, there is a marked difference between 

 these east and west sides and the northern face of the rocks. The 

 latter is not only extremely moutonnt, and when its nature admits 

 of it, or when it has been recently uncovered, finely polished, but 

 is powerfully striated and sometimes grooved, whilst the longer 

 or east and west sides only exhibit such features along a certain 

 distance, seldom exceeding more than one-third of the length of 

 the face in question, the remainder of which gradually loses all 

 traces of denudation and exhibits no more striae towards the rough 

 and wholly unaltered southern extremity (see fig. 12). I mention 



Fig. 12. 



^ 



!>v 



In this diaf^am is seen, as indeed in those preceding, the gradual disappearance of the striation 

 and wear of the lateral surfaces of the rocks from their northern to their southern ends. 



this fact, because it seems to coincide very well with the hypo- 

 thesis, that powerful currents from the north, carrying vast musses 

 of detritus and sand with them, impinged with great violence and 

 exercised a powerful friction on the northern or wc.ather face of 

 each hummock which exposed a resisting front, whilst such resist- 

 ance would naturally diminish as the opposing promontory trended 

 off' into a flattencid side, the drift and materials simply rushing 

 through the often wide depressions betwe(!n the low and isolated 

 rocks and producing little or no lateral effect, except indeed in 

 the caec of narrow mountain gorges, wherein the lateral pre«8ure 



2 B 2 



