278 PKOCEEDrN-GS OF THE GEOLOGICAL SOCIETT. [Feb. 26, 



can never, either chemically or mechameally, produce a smooth and 

 regular surface by shaving away hard and soft parts alike, or by 

 cutting equally through crystals of a different nature, but must 

 always leave a surface minutely corresponding to the denudability 

 of the parts (of the crystals) of rocks; it can only roughen, or leave a 

 surface more or less zigzag in profile. In Devonshii'e and elsewhere, 

 on all granites used in building, atmospheric weathering leaves a 

 surface rough in proportion to the size and varied nature of the 



crystals, and never a smooth or uniformly curved outline." 



"A smooth or pohshed surface (not involved in the structure of 

 rocks) whether a plane , a curvilinear hollow ^- — ^, a curvi- 

 linear protuberance ^ — ^, or a curvilinear hole Q , can only be pro- 

 duced (leaving ice at present out of consideration) by human agency, 

 or naturally by water charged with sand or stones, and acting with 

 a force sufficient to overcome inequalities of structure to a certain 

 extent." The author verified these statements by appealing to the 

 street pavements, or curbings of granite and limestone, in Exeter, 

 Dawlish, and Teignmouth. He then described moulded surfaces of 

 limestone both exposed and protected by red loam, on the ^lendip 

 Hills. " They resemble works of art in consisting of curvilinear 

 heights, hollows, through-perforations, and grooves. The figures 

 are often geometrically exact. The hollows vaiy in depth, from 

 shallow saucer-like depressions to pot-shaped cavities. The through- 

 perforations are sometimes more than a foot in diameter, more or 

 less funnel-shaped, and as smooth and regular as if turned out in 

 a lathe. Xo phenomena at all resembling them are now in course 

 of being formed, excepting on sea -coasts, and in the channels of 

 rivers." '^ Fac-similes of them are to be found on many sea-coasts 

 at the present day." They are ground out by the gyratory action 

 of waves charged with sand, or by waves wielding a stone or stones. 

 The author concluded by describing an extraordinary assemblage 

 of regularly arranged limestone flags, like grave stones, with natu- 

 ral inscriptions consisting of grooves generally parallel, but often 

 bending round at nearly right angles — both trough-shaped and 

 running the whole length of the flag — very smooth and regular in 

 form, theii' profile resembling the letter U. He believed they could 

 not be explained by the action of land-ice, and thought that the 

 theory of the to-and-fro motion of sea-waves, laden with coast- 

 ice charged with stones, offered the most satisfactory explanation of 

 all the phenomena. They may be seen a short distance to the west 

 of ]Minera, near "Wrexham, on a limestone tableland marked Ty hir 

 on the Ordnance map. 



3. On a Steiixs'g Insta^^ce of Appakext Oblique LAiiiXAXioN 



in GPvAifiTE. By D. Mackintosh, Esq., F.G.S. 



(Absti'act.) 



Ix this paper the author draws attention to the resemblance, at 



first sight, presented by many of the tors and cliffs of granite on 



Dartmoor, to the forms assumed by the Millstone-grit in Yorkshire, 



