E. MINERALOGY AND GEOLOGY. 235 



E. MINERALOGY AND GEOLOGY. 



POT-HOLES, OR " GIANT KETTLES." 



It is not always that geological investigations have as their 

 object phenomena which are of general interest, and with, 

 which all are more or less familiar. This is certainly the 

 case, however, with the study of the "giant kettles" in the 

 neighborhood of Christiania, Norway, which has been lately 

 carried on by Professor Kjerulf and some of his students. 

 There is hardly a running stream in our country of any con- 

 siderable size which does not give proof of the power of wa- 

 ter and stones in motion in what are popularly called " pot- 

 holes." An eddy in the stream where the current is strong- 

 sets a few pebbles in revolution. These commence a depres- 

 sion, into which larger stones fall, and the grinding is con- 

 tinued until a cavity has been produced perhaps several feet 

 in depth, and almost perfectly round. These are often to be 

 observed, not only in stream beds, but also in rocks on the 

 sea-shore, where the rush of the tide must supply the motive 

 force. 



The famous "giant kettles" of Norway are simply "pot- 

 holes " on a larger scale, and produced in former times under 

 somewhat different conditions than we have at present. The 

 superstition of the people represents them as having been 

 made by giants. In some places, where the form is ob- 

 long and irregular, fancy has seen in them the footprints of 

 these monsters, while in one place, where the road goes di- 

 rectly through a very large kettle, the saying is that there 

 St. Olaf turned his horse around. On the west coast of Nor- 

 way another name is used, and they are spoken of as giants' 

 chairs. 



The description of one of these kettles examined by Pro- 

 fessor Kjerulf will give some idea as to their size and general 

 character. At the surface it had a diameter of about eight 

 feet, being slightly elliptical in form. It widened consider- 

 ably on the descent, and then contracted again at the bot- 

 tom. It is interesting to note that the walls were distinctly 

 worked out in a spiral, which could be traced from top to 



