Carlow Natural Resources
The county lies between the great eastern granite district of the county of Wicklow and the coal formation of the Queen's county and Kilkenny. The granite shews itself along the south-eastern verge, in the mountainous range of Mount Leinster and Blackstairs, where it is interrupted by the precipitous valley of St. Mullins, but it appears again at Brandon hill, in the southern part of Kilkenny. The coal country is surrounded by and rests upon limestone, the strata of which, wherever examined, present appearances extremely similar. The description of the limestone valley between the granite country; two miles east of the town of Carlow, and the coal field as far westward, may serve to give a clear idea of the general nature of this part of the country. At the base of Browne's hill, two miles east of Carlow, the granite is covered with stratified silicious limestone, dipping 60° west of north at an angle of 10° from the horizon: the colour is light greyish blue, with numerous petrifactions, chiefly bivalve shells; it is calcined with great difficulty, and gives, on analysis, of carbonate of lime, 95.00; of silica, with a tinge of iron, 4.50; and of carbon, 0.50.
The stratification is quite regular between the granite country and Carlow, but with a change of colour and character as it recedes from the mass of granite. At first it changes to a dark blue, and madrepores are visible in it. The beds are extremely vesicular, and their numerous cavities are coated with a series of different fossils. On approaching Carlow, the limestone becomes more silicious and of a deeper colour: at the town the colour is dark or iron grey, and the texture fine-grained, and it is sometimes polished and used for chimney-pieces: to the west of the town the limestone is lighter in colour and much purer. Here the Lydian stone begins to appear in quantity, both in irregular beds and round nodules. The stone becomes still lighter in colour and finer in quality as it approaches the west. Some specimens from the higher quarries were found to contain solely carbonate of lime, with a small residuum of carbon, not amounting to a quarter per cent. The number of petrifactions in the upper quarry is immense, comprehending a great variety of fossil productions.
On approaching the point where the coal strata join the limestone, the stratification is generally disturbed; the rock becomes shivery and breaks into indeterminately angular small fragments. The quantity of Lydian stone is greatly increased; the actual point of contact between the limestone and coal being scarcely visible, on account of the disturbance of the strata. The Lydian stone appears to pass into slate clay,no division existing between them. The succession of rocks visible at Old Leighlin, is as follows, commencing from the bottom: dark blueish grey limestone, 10 feet; irregular black Lydian stone, with silicious petrifactions, 2 feet; light grey limestone, 20 feet; Lydian stone, with numerous silicious petrifactions, 3 feet; flinty slate, in very thin beds, the uppermost of which graduate into slate clay, and contain balls of clay ironstone of a dark blue colour, 30 feet; and sandstone flag, 200 feet. This stone continues to the summit of the hill, where it varies very much in quality, and passes from soft sandstone into soft micaceous slag, which divides into thin laminae from one-tenth of an inch to an inch in thickness.
Besides the irregularities above described, beds of brown spar rock are met with near the point of junction of the two formations; but they are more frequent on the southern and western boundaries than on the northern and eastern. The limestone field abounds with, rolled calcareous masses, pebbles, gravel, sand and marl, forming escars of considerable elevation, in which the calcareous gravel and sand frequently exhibit a stratified disposition with layers very distinct from each other. Carlow is almost exclusively an agricultural district.