6 Wynne — Denudation and its Causes. 



These — together with the absence of continuous terraces on moun- 

 tains ; ' not formed of horizontal limestone, but lying between these 

 limestone districts, while it may fairly be supposed that all were sub- 

 merged at the same time, — are points tending to throw doubt upon the 

 marine origin, of certain of these cliffs and terraces (the crags and fis- 

 sirres of which aboimd in evidence to prove the powerful action of rain 

 water) : for it can hardly be supposed that the sea had power to form 

 cliff-lines only out of limestone or horizontal strata : the coast of the 

 intervening mountainous country formed of other rocks in various 

 positions, presenting some of the finest examples of sea cliffs along 

 this part of the Atlantic shore. 



Isolated Pillars and Openings, — We may find instances of isolated 

 rocky pillars upon hills the very aspect of which suggests that the 

 stone is being gradually disintegrated by rain, (such as are repre- 

 sented in Figs. 1 and 2 Plate I),* and also along coast-lines where 

 they are as evidently the results of marine denudation (an example 

 being given in Fig. 3, Plate I).^ 



In like localities natural openings may be sometimes found tun- 

 nelled through rocks, thus a vacant space allows the light to be seen 

 through the profile of one of the rugged rain- worn hills on the south 

 side of the Great Indian Peninsular Eailway, at some distance from 

 the Lanowlee station in the Deccan ; and another remarkable in- 

 stance occurs in the sea cliffs of Innishnabro, one of the Blasket 

 Islands, off the coast of Kerry, where the nearly vertically bedded 

 rocks are pierced by large openings one above the other (Plate 11., 

 Fig. 7). 



These examples will ^how, not so much that they are in both cases 

 evidence of marine action, as that either marine or sub^rial agencies 

 may under certain conditions produce similar forms, 



Sulcerial Denudation of Limestone, etc. — SubEerial denudation is 

 perhaps most plainly visible upon limestone rocks. At all events 

 its powerful influence upon them cannot be denied, whether observed 

 on cliffs or upon mountain slopes, in the peculiar rain channels with 

 which the rock is sometimes furrowed, in caves and subterranean river 

 courses, or where boulders of different kinds rest upon pedestals of 

 this rock, marking the depth to which surrounding portions of the 



1 My friend, Mr. Kinahan, in his paper, " Notes on some of the Drift in Ireland." 

 — Eoyal Geol. Soc, Ireland, March 4, 1866 — speaks of lines of cliff in the hills of Yar 

 Connaught. The cliffs alluded to are supposed to be of the disconnected kind (of 

 which that at Coomassig is given as an example) : their marine origin not being 

 strongly suggested by their appearance, which certainly differs widely from that of 

 the continuous cliffs and terraces in either the Burren or Sligo districts. Their oc- 

 currence between certain sets of contour lines related to sea level may be as much a 

 matter of course or of accident as the result of marine action, unless it can be proved 

 that the whole country was elevated equally, or at the same rate, with reference to 

 •the present horizon. 



2 Fig. 1 . — From a trappean hill at "Wassid near the foot of the Inclines by which 

 the Gt. Indian Peninsular Eailway crosses the Western Ghats. Fig. 2. — Part of a 

 sketch from the elevated hill station of Matheran, between the Ghats Proper and 

 Bombay, — (Trap rock). 



^ Fig. 3. — "The Old Man Rock" formed (as well as can be recollected) of Purple 

 Grit. Mouth of Bulls Creek, South-side of Dingle Promontory, Ireland, 



