52 W. A. E. USSHER ON TERMINAL CURVATURE 



On a hilltop half a mile W.N.W. of Goodrington, near Paignton, 

 I observed a large weatherworn limestone bonlder lying on the sur- 

 face, with several perforations extending from ^ to 1 \ inch from 

 the surface, and making angles of from 30° to 80° with it. The sides 

 of the cavities were generally smooth ; in two of them dead shells, 

 apparently of Helix nemoralis in a fragmentary condition, were dis- 

 covered. The boulder occurs at more than 200 feet above the sea. 

 It may have been brought there, though for what purpose it is 

 hard to say. 



Granting the subsidence of this part of Devon to a depth of 

 300 feet, the absence of any corroborative evidence elsewhere proving 

 subsidence to a greater extent than the maximum height of the 

 raised beaches precludes the ascription of a corresponding depres- 

 sion to other parts of Devon and to Somerset and Cornwall. 



The amount of meteoric abrasion that must have taken place 

 since the raised-beach formation would be more likely to cause the 

 obliteration of perforated rock-surfaces (those observed being in 

 exposed situations, and having, I believe, lately disappeared) than to 

 remove all traces of a sea-wrought configuration. 



How far certain species of land-shells may be capable of dissolv- 

 ing out cavities in limestone rocks has not, I believe, been ascertained. 



These considerations are adverse to suggestions involving a partial 

 submergence to the depth of a few hundred feet. 



Even conceding the most favourable physical conditions, I am at 

 a loss to conceive how any oceanic current, no matter how powerful, 

 could twist back the laminae of the most flexible shales, except as 

 directing the course of floe, pack, or berg ice. 



Mr. Mackintosh's last suggestion, of a violent rush of waters 

 occasioned by a sudden upheaval, or depression, savours more of 

 cataclysm than connexion in any way with the phenomena under 

 consideration. 



If the " weight of the hill " means any thing, it merely expresses 

 conditions favourable to the production of slips, by percolating waters 

 rendering a clayey substratum slippery, by the action of wedging 

 frosts, or similar agencies. If it were a natural force, capable of 

 producing reversal in shales outcropping on slopes, terminal curves 

 would be confined to hillsides and would be of much more frequent 

 occurrence than they are, 



Transportation of Blocks. 



Under this head Mr. Mackintosh notices on Brendon Hill " a con- 

 siderable thickness of reddish loam w overlying slaty debris and in- 

 termixed with fragments of slate and quartz blocks of large size, the 

 latter being " at considerable distances from their native veins." 

 He ascribes the transport of these blocks to the agent which 

 caused the displacement of the slaty laminae, or to " a subsequently 

 operating cause." This is evidently an instance of Head, a name 

 applied to the accumulation of loam with angular stones so fre- 

 quently exposed in the Palaeozoic cliffs of Devon and Cornwall, 



