Correspondence — Mr. W. A. E. Ussher. 237 



COiaiRIESIPOn^IDIBISrCIE!. 



ON TEEMINAL CURVATURE IN THE SOUTH-WESTERN COUNTIES. 



Sir, — Notwithstanding its ten years' rest, this subject seems to 

 retain its marrow as a bone of contention, judging from Mr. Mackin- 

 tosh's letter in your last Number. Mr. Mackintosh seems to have 

 mistaken the object of my paper, as I had of his ; for had I known 

 that " none " of the solutions proposed by him were " confidently 

 advocated," by making the real object of my paper more prominent, 

 and dwelling less upon his hypotheses; I might have appeared less 

 controversial. The principal object of my paper was to deprecate 

 the invocation of glacial action in explanation of phenomena other- 

 wise more reasonably explainable, and especially so in districts 

 where all direct proof of glaciation is wanting. 



The keynote of my objection to all Mr. Mackintosh's explanations 

 is struck in his declared scepticism in a " great surface waste and 

 contour moulding" of the South-western Counties during Pleisto- 

 cene times. How any geologist can calmly contemplate the distant 

 table-land of the Blackdowns from its insulated remnant Haldon, 

 and gazing across the broad valley of the Exe, excavated entirely 

 since the accumulation of the clay with flints, deny the vast contour 

 moulding and surface waste of Pleistocene ages, it is difficult to con- 

 ceive. I can only regard the hypotheses alluded to by Mr. Mackintosh 

 as untenable as regards the " Head " of Devon and Cornwall, having 

 a very wide acquaintance of the facts, and feel that I must hide my 

 diminished " Head" under some more congenial covering than an 

 Arctic Sea or " immense ice-water lake." My idea of a greater 

 elevation of land, accompanied by a more rigid expression of the 

 present causes of subaerial waste, not only suffices to explain the 

 formation of " Head " proper (i.e. the angular accumulation of stony 

 loam intermediate in time between the elevation of the beaches 

 and the submergence of the forests), but also fits into a necessary 

 sequence of physical changes. 



I do not believe in uniformity of direction of curved-back laminee, 

 such directions being dependent on dip and strike of cleavage planes. 

 The effect of roots in wedging off laminae is very local, seldom 

 causing reversals extending more than a few feet from them. I 

 must, in conclusion, apologize to Mr. Mackintosh for having mis- 

 understood him about the direction of the cleavage planes on the 

 northern slopes of Brendon Hill ; my objection to ice-passage on 

 the ground of the absence of terminal curvature, consistently with 

 his theory, on the north slope, was based on the assumption that the 

 laminae inclined in a southerly direction at a high angle, but not 

 approximating to the vertical. Any apparent controversial spleen 

 in the foregoing remarks must be attributed to that pardonable 

 partiality for their own specialities generally exhibited by local 

 geologists, and to no unfriendly spirit as regards Mr. Mackintosh. 



W. A. E. USSHEK. 



