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II.—On Denudation with reference to the Configuration of the Ground
Published online by Cambridge University Press: 01 May 2009
Extract
The consideration of the subject of Denudation requires so extensive an acquaintance with Forms of the Ground in a field large enough to embrace all countries, that general conclusions must be advanced with more or less reserve, in proportion to the extent of our research.
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References
page 3 note 1 Geology of the Moon—Geol. Mag., Vol. iii., p. 141.Google Scholar
page 3 note 2 Wm., Carter M.B., Plurality of Worlds.—Quart. Jour. Science, p. 232.Google Scholar
page 4 note 1 See Prof. Ramsay's paper, on Lake Basins.—Quart. Journ. Geol. Soc. vol. xviii. 1862.Google Scholar
page 5 note 1 See Mr. Maw's paper.—Geo. Mag., No. 28.Google Scholar
page 5 note 2 Since the above was written a very similar observation has appeare in a paper upon five typs of Earth' surface, in the United States, by Mr. Lesley
page 6 note 1 My friend, Mr. Kinahan, , in his paper, “Notes on some of the Drift in Ireland.”—Royal 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 certainlydiffers widely from that of the continuous cliffs and terraces in either the Burren or Sligo districts. Their occurrence 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.Google Scholar
page 6 note 2 Fig. 1.—From a trappean hill at Wassid near the foot of the Inclines bywhich the Gt. Indian Peninsular Railway crosses the Western Ghats. Fig. 2.—Part of a sketch from the elevated hill station of Matheran, between the Ghata Proper and Bombay,—(Trap rock).
page 6 note 3 Fig. 3.—“The Old Man Rock” formed (as well as can be recollected) of Purple Grit. Mouth of Bulls Creek, South-side of Single Promontory, Ireland.
page 7 note 1 Numerous instances of the slow rate at which even limestone weathers, and therefore the enormous time required to produce results so evident, are familiar to most observers. An inscribed slab of this rock in the interior face of the battlement of a bridge, a couple of miles west of Athlone, although somewhat weathered, distinctly showed in the year 1862, a date 100 years previous. Another limestone slab in a very similar situation, facing the E.S.E., (The Liberty Stone), at Whitehall Bridge, near Limerick, has an inscription, in raised characters, about one-eighth of an inch relieved. The stone is but slightly weathered; the inscription, except in the last figure of the date, is perfect, and the date is 1635. The preservation of glacial strisa upon some smooth surfaces of limestone, indicates a certain variability in amount of subaerial action.
page 7 note 2 The absence of references prevents further allusion here to the subject of valleys which are lower than sea-level or those which being valleys of denudation discharge water over rock barriers at a greater height than that of their interior parts. The glacial origin of these will be found discussed in Professor Ramsay's paper to the Geol. Soc. Lond., Vol. xviii., p. 185.Google Scholar
page 7 note 3 See “On Watersheds, by Geo., Maw F.G.S. etc.— Geol. Mag. Vol. III. No. 8, p. 344.” and the outline of the S. W. Coast of Ireland.Google Scholar
page 8 note 1 The Valley of which is attributed to subærial denudation by Professor Jukes in his able paper and interesting letter, See Quart. Journ. Geol. Soc. Lond., Vol. xviii., and Geological Magazine, Vol. III., No. 5, p. 232.Google Scholar
With reference to the foot note to Mr. Kinahans paper. “On the Rock basin of Lough Corrib,” Geological Magazine, Vol. III., (Nov. 1866,) p. 495.—Supposing the morass mentioned to be below high water mark, if a sand bar was thrown up by the sea, the swamps behind it would naturally become a receptacle for peat independently the prior submergence of other localities. The argument requiring the former existence of sand bars around so much of the bolder coasts of Ireland, hardly explains their wholesale removal, while the supposition of depression would agree with the similar occurrence on the East Coast of England. (See Mr. J. Geikie's paper “On the Forests and Peat Mosses of Scotland. Trans. Rl. Soc., Edin., Vol xxiv). In the example at Youghal a beach has been thrown up above and resting on the peat, which is said to extend out beneath the bay at low water, and was observed when the tide was very far out, or nearly at its lowest, beneath the sea as far as footing could be obtained.Google Scholar
page 8 note 2 Among many examples showing somewhat of the rate of erosion effected by the sea, the case of the all but pre-historic Beehive Village of Fahan, in Kerry, may be mentioned a portion of which remains upon the verge of the sea cliffs at Slea Head: or the tradition that Horse Island has been detached oy the sea from Bolus Head in the same county; similar instances, save in the softer nature of the materials removed, are the old Abbey and graveyard encroached upon by the sea at Ballinskelligs Bay, near the latter of the above localities, and the ancient graveyard ofMahim, partly washed away at the northern extremity of Bombay Island.
page 9 note 1 In his paper “On River Valleys of the South of Ireland.” Quart. Journ. Geol. Soc., London, Nov., 1862 (p. 402).