138 Correspondence. 



ments. Large bodies of water in the shape of marine currents, or 

 " waves of translation," caused by sudden elevations,' ought not, I 

 think, to be rejected as a cause, until their inadequacy has been 

 clearly shown.'^ Should the theory of great bodies of water be 

 ultimately found untenable, then equally great bodies of moving ice 

 would, I think, furnish a more satisfactory explanation than rain. 



Water-worn cliffs, pillars, and rock-surfaces. — Since I first directed 

 attention to traces of sea-action on certain inland rocks, several 

 geologists have shown an increasing disposition to limit their con- 

 fidence in atmospheric denudation. Admitting that rain acts power- 

 fully on arable fields, roads, exposed beds of sand and gravel, and 

 soft rocks, I asserted that pure rain-water has little or no influence 

 on hard rocks (in this, I now find, I was forestalled by Colonel 

 Greenwood) ; that the preservation of glacially smoothed and striated 

 surfaces demonstrates the inadequacy of mere rain to denude hard 

 rocks : that if ice-marks have endured, it is reasonable to look for 

 marks left by the sea ; that they may be found on inland cliffs, and 

 rock -pillars, which present smoothed^ and rounded forms, or which 

 have been left with angular projections, where the adjacent blocks 

 (of equal hardness) have been displaced or removed;^ that the 

 summits, ridges, and sides of many hills, present marks which are 

 facsimiles of those now in course of being formed by the sea ; that 

 these marks may be distinguished from the efi'ects of glaciation, by 

 their consisting of a succession of small hollows, ridges, round, oval, 

 or elongated pot-holes, or short grooves, indicating the gyratory or 

 to-and-fro action of stones in water. I have found these phenomena 

 not only on Mynydd Gader, at a lower level than the glaciated sur- 

 faces lately discovered by Mr. Wallace (Quart, Jour, of Sc, Jan., 

 1867), and on elevated natural pavements of limestone near Minera, 

 but on the Mendip Hills, where the smooth and almost polished pot- 

 holes are very numerous and striking. Mr. Plant (Geol. Mag., 

 Feb., 1867, p. 81) has lately discovered an old sea beach on the lime- 



1 Such as must have resulted from these sudden upstarts of the sea-hottom, which 

 are indicated by the transverse horizontality of many systems of terraces now at con- 

 siderable altitudes above the level of the sea. (See account of Eaised Beaches near 

 Llangollen, in Geol, Mag., Sept. 1866, Fig. 13, in the plate, which furnishes a 

 very inadequate representation.) 



* It is remarkable that such submarine troughs as Captain Beechey's " Ditch in 

 the North Channel" should not have been more particularly examined with reference 

 to denudation. 



2 In Geol. Mag., Nov. 1866, p. 618, Dr, Lindstrom thinks I have mistaken glacial 

 grooves for wave-marks. An inspection of the locality would, I think, convince any 

 unbiassed geologist that they occur in situations, and are associated with phenomena, 

 such as shallow pits and caves, which furnish a strong presumption against a glacial 

 origin. 



* Mr. "Wynne, in asserting that it is impossible to distinguish between rock-pillars 

 formed by the atmosphere, and those formed by the sea, unintentionally ignores the 

 validity of that dualogical reasoning on which geology is founded. Even dynamically 

 considered, there can be no doubt that the efi'ects of a slow vertical agency can be 

 easily distinguished from phenomena produced by the lateral undermining, and to-and- 

 fro action of the sea. Mr. Kinahan, in answer to Mr. Wynne, has brought forward 

 a convincing illustration of the marine origin of rock-pillars (Geol. Mag., Feb., 1867, 

 p. 89). 



