629 



BOG. 



BOG. 



630 



it rises to a level with its lowest boundary, where it becomes the 

 source of a stream or river, and forms a lake. The mud being 

 deposited at the bottom, gradually becomes a time peat, or is quite 

 reduced to its elementary earths. In this case it may become a 

 stratum of rich alluvial soil, which some convulsion of nature may 

 lay dry for the benefit of future ages. From this circumstance has 

 arisen the great advantage of draining bogs, to which the attention 

 of agriculturists and men of science has often been profitably 

 directed. 



The boga of Ireland are estimated in the whole to exceed in extent 

 2,800,000 English acres. The greater part of these bogs may be con- 

 sidered as forming one connected mass. If a line were drawn from 

 Wicklow-Head on the east coast to Galway, and another line from 

 Howth-Head, also on the east coast, to Sligo, the space included 

 between those lines, which would occupy about one-fourth part of the 

 entire superficial extent of Ireland, would contain about six-sevenths 

 of the bogs ill the island, exclusive of mere mountain-bogs, and bogs 

 of no greater extent than 800 English acres. This district resembles 

 in form a broad belt drawn from east to west across the centre of 

 Ireland, having its narrowest end nearest to Dublin, and gradually 

 extending its breadth as it approaches the western ocean. This great 

 division is traversed by the river Shannon from north to south, which 

 thus divides the great system of bogs into two parts. Of these, the 

 division to the west of the river contains more than double the extent 

 of bogs in the eastern division, so that if we suppose the whole of the 

 bogs of Ireland (exclcusive of mere mountain-bogs, and of bogs of less 

 extent than 800 acres) to be divided into twenty parts, twelve of these 

 parts will be found in the western division, and five parts in the eastern 

 division of the district already described, while of the remaining 

 three parts, two are to the south and one to the north of that 

 district. 



The smaller bogs, excluded from the foregoing computation, are 

 very numerous in some parts. In the single county of Cavan there 

 are above 90 bogs, not one of which exceeds 800 English acres, but 

 which collectively contain about 17,600 English acres, without taking 

 into the account many bogs the extent of which is from five to twenty 

 acres each. 



Most of the bogs which lie to the eastward of the Shannon and 

 which occupy a considerable portion of the King's County and the 

 county of Kildare, are generally known by the name of the Bog of 

 Allen. It must not however be supposed that this name is applied to 

 any one great morass ; on the contrary, the bogs to which it is applied 

 are perfectly distinct from each other, often separated by high ridges 

 of dry country, and inclining towards different rivers as their natural 

 directions for drainage. 



The surface of the land rises very quickly from the Bog of Allen on 

 all sides, particularly to the north-west, where it is composed to a con- 

 siderable depth of limestone gravel, forming very abrupt hills. In 

 places where the face of the hills has been opened the mass is found 

 to be composed of rounded limestone, varying in size from two feet in 

 diameter to less than one inch ; the largest pieces are not so much 

 rounded as the small, and frequently their sharp angles are merely 

 rubbed off. They are usually penetrated by contemporaneous veins 

 of Lydian stone, varying in colour from black to light gray. The 

 colour of the limestone is usually light smoke-gray, rarely bluish-black ; 

 when it is bluish-black the fracture is large conchoidal ; that of the 

 gray is uneven, approaching to earthy. The Lydian stone when unat- 

 tached to the limestone has usually a tendency to a rhomboidal form, 

 sometimes cubical ; the edges are more or less rounded ; the longitudi- 

 nal fracture is even, the cross fracture is conchoidaL 



The Grand Canal from Dublin to Shannon Harbour passes through 

 a considerable part of the great bog-district of Ireland. In forming 

 this canal it was necessary to make considerable embankments, the 

 surface-water of the canal being generally on a higher level than the 

 surface of the immediately adjoining bogs. Where this was not the 

 case advantage was taken of the circumstance to conduct the drainage 

 of the bogs into trenches for the supply of the canal 



The bogs situated to the south of the great belt in the centre of 

 Ireland occur in Tipperary, Kilkenny, Clare, and Queen's County ; 

 those to the north of that belt occur in Antrim, Down, Armagh, Tyrone, 

 and Londonderry. 



It appeared from the examination of the surveyors appointed by 

 parliament in 1810 to investigate the nature and extent of the bogs in 

 Ireland, that they consist of " a mass of the peculiar substance called 

 peat, of the average thickness of twenty-five feet, nowhere less than 

 twelve nor found to exceed forty-two this substance varying mate- 

 rially in its appearances and properties in proportion to the depth at 

 which it lies. The upper surface is covered with moss of various 

 species, and to the depth of about ten feet is composed of a mass of 

 the fibres of similar vegetables in different stages of decomposition, 

 proportioned to their depth from the surface, generally however too 

 open in their texture to be applied to the purposes of fuel ; below this 

 generally lies a light blackish-brown turf, containing the fibres of moss, 

 still visible though not perfect, and extending to a further depth of 

 perhaps ten feet under this. At a greater depth the fibres of vege- 

 table matter cease to be visible, the colour of the turf becomes blacker 

 and the substance much more compact, its properties as fuel more 

 valuable, and gradually increasing in the degree of blackness and com- 

 KAI. mat. DIV.VOL. I. 



pactness proportionate to its depth ; near the bottom of the bog 

 it forms a black mass, which when dry has a strong resemblance 

 to pitch or bituminous coal, having a conchoidal fracture in every 

 direction, with a black shining lustre, and susceptible of receiving a 

 considerable polish." 



The surface of Irish bogs is not in general level ; indeed it is most 

 commonly uneven, sometimes swelling into hills and divided by val- 

 leys, thus affording great facilities for drainage. None of the bogs of 

 Ireland which have been described occur on low ground, a fact which 

 seemed to strengthen the opinion of their having always originated 

 from the decay of forests. This theory of the original formation of 

 bogs was at one time very generally adopted, but the result of more 

 recent investigations shows that it cannot be supported. That some 

 bogs may have been formed in this manner is not denied. It is stated 

 in the ' Philosophical Transactions,' No. 275, that " the Romans under 

 Ostorius, having slain many Britons, drove the rest into the forest of 

 Hatfield (in Yorkshire), which at that time overspread all the low 

 country ; and the conqueror taking advantage of a strong soxith-west 

 wind, set fire to the pitch-trees of which the forest was chiefly com- 

 posed, and when the greater part of the trees were thus destroyed, the 

 Koman soldiers and captive Britons cut down the remainder, except a 

 few large ones, which were left growing as remembrancers of the destruc- 

 tion of the rest. These single trees did not long withstand the action 

 of the winds, but falling into the rivers intercepted their currents, 

 and caused the waters to rise and flood the whole flat country ; hence 

 the origin of the mosses and mooiy bogs which were afterwards 

 formed there." This moorland near Hatfield, seven miles north-east 

 from Doncaster, and about Thorne, is now a boggy peat covered with 

 heath, several feet higher than the adjoining land, and very wet ; 

 whence it has been aptly compared to a sponge full of water. The 

 Thorne waste with some adjacent tracts and the Hatfield Moor contain 

 about 12,000 acres. 



Underneath the peat in many places the layers of trees are found 

 which serve to confirm this theory of the origin of these bogs. Some 

 of them give indications of having been felled by human agency. 



In the ' Ordnance Survey of the County of Londonderry,' presented 

 by Lord Mulgrave to the British Association during its meeting 

 (Aug. 1835) in Dublin, are some remarks on the subject which are 

 deserving of attention : 



" In the production of bog, Sphagnum [Sphagnum palustre] is 

 allowed on all hands to have been a principal agent, and superabund- 

 ant moisture the inducing cause. To account for such moisture various 

 opinions have been advanced, more especially that of the destruction 

 of large forests, which by obstructing in their fall the usual channels 

 of drainage, were supposed to have caused an accumulation of water. 

 That opinion however cannot be supported ; for as Mr. Aher remarks 

 in the ' Bog Reports,' such trees as are found have generally six or 

 seven feet of compact peat under their roots, which are found standing 

 as they grew, evidently proving the formation of peat to have been 

 previous to the growth of the trees, a fact which in relation to firs may 

 be verified in probably every bog in this parish, turf from three to 

 five feet thick underlying the lowest layer of such trees. This fact is 

 indeed so strongly marked in the bog which on the Donegal side 

 bounds the road to Muff, that the turf-cutters having arrived at the 

 last depth of turf, find timber no longer, though formerly it was 

 abundant, as is proved by their own testimony, from experience, and 

 by the few scattered stumps which still remain resting on the present 

 surface. Not so however with oaks, as their stumps are commonly 

 found resting on the gravel at the base, or on the sides of the small 

 hillocks of gravel and sand which so often stud the surfaces of bogs, 

 and have by Mr. Aher been aptly called islands. He further adds that 

 in the counties of Tipperary, Kilkenny, &c. they are popularly called 

 Derries (signifying ' a place of oaks '), a name deserving attention whe- 

 ther viewed as expressive of the existing fact or as resulting from a 

 lingering traditionary remembrance of their former condition, when, 

 crowned with oaks, they were distinguishable from the dense forest 

 of firs skirting the marshy plains around them. The strong resem- 

 blance to ancient water-courses of the valleys and basins which now 

 contain bogs, and the occurrence of marl and shells at the bottoms of 

 many, naturally suggest the idea of shallow lakes, a view of the subject 

 adopted in the ' Bog Reports ' by Messrs. Nimmo and Griffiths. Such 

 lakes may have originated in the natural inequalities of the ground, or 

 been formed by the choking up of channels of drainage by heaps of 

 clay and gravel, or they may have been reduced to the necessary state 

 of shallowness by the gradual wearing away of obstacles which had 

 dammed up and retained their waters at a higher level." 



The probable process of the formation of bog in such cases is thus 

 explained in the ' Ordnance Survey : ' " A shallow pool induced and 

 favoured the vegetation of aquatic plants, which gradually crept in 

 from the borders towards the deeper centre. Mud accumulated round 

 their root and stalks, and a spongy semi-fluid mass was thus formed, 

 well fitted for the growth of moss, which now, especially Sphagnum, 

 began to luxuriate. This, absorbing a large quantity of water and 

 continuing to shoot out new plants above while the old were decaying, 

 rotting, and compressing into a solid substance below, gradually 

 replaced the water by a mass of vegetable matter. In this manner 

 the marsh might be filled up, while the central or moister portion 

 continuing to excite a more rapid growth of the moss, it would be 



2 M 



