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 Decries (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 I 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 semifluid 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 gradually raised above the edges until the whole surface had attained an elevation sufficient to discharge the surface-water by existing chan nels of drainage, and calculated by its slope to facilitate their multiage, when a limit would be in some degree set to Its further increase.' According to the personal observations of Mr. Griffiths, made during many years, the growth of turf In these bogs is very rapid, amounting sometimes to two inches in depth in one year : this however is stated to be an excessive growth under peculiarly favourable circumstance& The roots which were attached to the groond decay, and the whole of the surface becomes a floating mass of long interlaced fibres which when taken out has been significantly called in Ireland Old Wives Tow.' The black masa of the bog is a mud almost entirely formed of decomposed vegetable fibres, but not of sufficient specific to sink to the bottom ; thus producing that semi-liquid state which distinguishes a quaking bog from a peat-moss. The vegetation which continues on the surface and at some depth below has the appearance of a Soo green turf. In many cases the roots are so matted together and so strong as to form a web capable of bearing the gentle and light tread of a man accustomed to walk over bogs, bending and waving under him without breaking ; andnvhile a person unskilfully attempting to walk upon it would infallibly break through and be plunged in the bog like a venturous skater on unsound ice, the prac tised bog-trotter ' with proper precautions passes over them in safety. This has often been of considerable advantage in war or in the pursuit of illegal employments. The fugitive escapes over his native bogs where the pursuer cannot venture to follow, or if he does he generally pays the penalty of his ignorance or by sinking in them.