162 Professor Naumann on Smoothed Bock Surfaces. 



and polished rock-surfaces ; and although these small emi- 

 nences of our otherwise level country, neither by their form, 

 nor by their height, remind us in any respect of the Alps, 

 yet we are astonished by finding, on their surface, pheno- 

 mena of attrition similar to those which are so frequently 

 exhibited by the rocky bottoms of the Alpine valleys. If any- 

 thing whatever could justify the almost ironical appellation 

 of " Hohburger Schweitz," it would certainly be this re- 

 markable phenomenon which the diminutive hills of our range 

 possess in common with the colossal mountains of the Al- 

 pine regions. 



On closer inspection, the smoothings of the rock surfaces 

 among the porphyritic hills of Hohburg, although they have 

 a general resemblance to those of the Alps, are yet found to 

 be sufficiently distinct from them, to prevent us from being 

 entitled at once to identify the two with one another, or at- 

 tribute them both to the same cause. The smoothed sur- 

 faces, indeed, exhibit among themselves so much difference 

 of character, as to render it necessary to separate them pri- 

 marily into two divisions. Those of the one kind are really 

 surfaces smoothed by grinding ; while the others can only be 

 called surfaces of erosion. Both occur only on the exterior 

 of the rocks, or of the blocks which have been broken away 

 from them. On the blocks they sometimes occur on two 

 sides, and even in various directions on the same side ; but, 

 on the solid rocks, the scratches always agree with one ano- 

 ther in their direction, although that direction is in some 

 degree dependent on the locality. 



From the whole of the phenomena, Naumann draws at last 

 the following conclusions : — 



(1.) The grinding and eroding material can have been, for 

 the most part, nothing else than finely comminuted stone, 

 such as is met with in the sand and sandy clay of the dis- 

 trict. This is indicated by the great uniformity of the at- 

 trition, the constant formation of the same pattern on the 

 same scale, the small length, breadth, and depth of the 

 scratches, the entire absence of large and greatly lengthened 

 grooves, the sharpness of the edges of such blocks of porphyry 



