November, 1902.] 



KNOWLEDGE 



243 



(oufludes, with much reasoD, that it is prohablv U^ l>e 

 sought iu a jjradvially diininishinir rainfall. 



Tlieiv is another manner in which a bog may meet 

 destruction —a way which is always dramatic, and some- 

 times may involve serious catastrophe. This happens 

 when, owing to continual growth, the bog becomes 

 unstable, and either slides bodily, or ruptures its walls and 

 emits its contents. In order to understand how this takes 

 place, we must study the structure of a bog. Tlie thirty 

 or forty feet of material which in a largc> peat-bog se])arates 

 the surface from the underlying solid ground is not by 

 any means of a consistency as firm as that of the surface 

 layer. The intertwining stems and roots of the growing 

 plants form a light matted felt which is comparatively 

 firm, esj)ecially towards the margins of the bog ; iu the 

 centre there are often holes in the crust, filled with mud 

 or water, and connecting with the interior. This interior 

 is tluid compared with the crust. The decomposed matter 

 of the surface layers sinks to the bottom, and may form 

 there a comparatively dense deposit, but the middle layers 

 consist of thin inul. aivl '>ften contain vast quantities of 



An ol,l Ti 



Atliintic; Co. Sligo. 



fE. Welch, Photo. 



■water, -which either descend from the surface in wet 

 weather, or ascend from springs in the bottom of the bog. 

 The felted crust is usually sufficiently strong to resist the 

 pressure of the semi-fluid interior, even on large bogs which 

 are situated on sloping ground ; but exceptional circum- 

 stances may cause rupture An unusually wet season may 

 swell the bog beyond the ]>oint of stal>ility : or the 

 stoppage of underground channels may cause great 

 gatherings of water, and ultimate collapse of the crust ; 

 or turf-cutting injudiciously carried out may weaken the 

 margin of the bog ; and a bog-flow may result. These flows 

 vary greatly iu their character. The bog may slide bodily 

 forward over its more fluid layers, so that the movement 

 resembles a land-slide. This is, for instance, what 

 happened in Joyce Country, Connemara, in September, 

 1821, when "upwards of a hundred acres of land, on 

 which crops were growing and several families resided, 

 were heard to emit a sound resembling thunder ; th-- earth 

 then became convulsed, and eventually this large tnict 

 moved down towards the sea, leaving the whole routejover 



which it passetl <a complete waste."* A quaint and in- 

 teresting account of a similar occurrence in Co. Limerick 

 in 1(!!I7 may b(> read in the Phihiixiphical Tranfiftrlhnsf : — 

 " On the 7th day of .Tune. lOH", near Clirirhrlllt\ in the 

 County of Liiiicrlrk. in Ireland, a great Rumbling, or 

 faint Noise, was heard in the Earth, much like unto a 

 Sound of Thunder near spent ; for a little Space the Air 

 was somewhat troubled with little Whisking Winds, 

 seeming to meet couirary Ways : And soon after that, to 

 the (ircater Terror and Afrightment of a great Number of 

 Spectators, a more wonderful thing happened ; for in a 

 Bog stretching North and South, the Earth began to move, 

 viz., Meadow and Pastvire Land that lay on the Side of 

 the Bog. . . . This Motion began about Seven of the 

 Clock in the Evening, llmtuatingin its Motion like Waves, 

 the Pasture-Laud rising very high, so that it over-run the 

 ground beneath it, and moved upon its Surface, rowling 

 on with great j)usliing violence, till it covered the 

 Meadow, and is held to remain upon it 16 Feet. . . ." 



In many other cases the bog has burst instead of slid. A 

 few reports of such occurrences may be quoted : — 



" A large bog of 1500 acres, lying between Dundrum 

 and Cashel, in the County of Tipperary, began to be 

 agitated iu an extraordinary manner, and to the astonish- 

 ment of and terror of neighbouring inhabitants. The 

 rumbling noise from the bog gave the alarm, and on the 

 oOtli it burst, and a kind of lava issued from it ... . 

 oversjireading and laying waste a fine tract of fertile land. 

 .... Everything that opposed its course was buried in 

 ruins. Four houses were totally destroyed, and the trees 

 that stood near them torn up by the roots.":[: Again, 

 "After a sudden thaw of snow, the bog between Bloom- 

 field and Geevah [Co. Sligo] gave way ; and a black deluge, 

 carrying with it the contents of 100 acres of bog, took the 

 ilirection of a small stream, and rolled on with the violence 

 of a torrent, sweeping along heath, timber, mud and stones, 

 and overwhelming many meadows and arable land. On 

 j.nssing through some boggy land, the flood swept out a 

 wide and deep ravine, and a part of the road leading from 

 Bloom field to St. James's Well was completely carried 

 away from below the foundation for the breadth of 200 

 vards."§ In some cases the disturbance, at least at first, 

 was local, and clearly caused by the undue accumulation 

 of water, presumably owing to stoppage of the ordinary 

 drainage channels. For instance, from an account of the 

 bursting of a bog in Co. Antrim iu 1835, sent to the 

 Magazine of Natural Hidory,\\ we gather that during one 

 day a portion of the surface of the bog swelled up till the 

 convexity was 30 feet in height, when with a noise like a 

 i-ushing "wind, it sank several feet, ejecting tufts, mud, and 

 water; two davs later the same movement was repeated, 

 and eventually a great discharge of mud and water took 

 place. The liquidity of the discharged interior varies 

 greatlv in different cases. As we have seen from some of the 

 quotations above, the flow sometimes assumes the form of 

 a rapid torrent. On the other hand, iu one instance a 

 farmer, digging potatoes, looks up to discover a brown 

 mass creeping across the field towards him.^ And Sir 

 William Wilde states that in the well-known bog-flow of 

 Kilnalady, in King's County, the bog-stuif " moved down 

 the vallev at the rate of about 2 yards an hour, with a 



* " Census of Ireland, 1851," Part V., Vol. I. p. 90. 1856. 



+ Phil. Trans., Vol. XIX., pp. 714-716. 1697. 



t Oentleman's Magazine, Vol. LVIII., p. 355. 1788. 



§ Lyell : " Principles of Geology," lOth Ed., Vol. II., p. 504. 



II Maff. Nat. Hist., Vol. IX., pp. 251-261. 1836. 



t Savage : " Picturesque Ireland," pp. 234, 235. 



