Page:Transactions of the Geological Society, 1st series, vol. 3.djvu/139

 existence of this formation near Metz. Its thickness in Ireland has not been ascertained.

4. The lias in Ireland reposes, as in England, on beds of red and variegated marle, containing gypsum and further distinguished by numerous salt springs; the marle is underlaid by a thick deposit of red and variegated sandstone containing clay galls. These four formations which, together with the basalt, constitute the whole mass of the mountains belonging to the third system, cannot be estimated as possessing a less average thickness than from 800 to 1000 feet: the whole system appears at the north-eastern and south-western extremities to repose upon the coal formation, and its associated limestone, and this again on transition or primitive rocks.

The four formations, more particularly specified, vary considerably in thickness in different places. The mulattoe and lias are often entirely wanting, so that the chalk rests on the sandstone No. 4: this position seems to arise from the superior stratum in such cases extending beyond the outgoings of one or more of the inferior strata, and being thus brought into contact with beds which, when the series is full, occupy a yet lower place.

The chalk and sandstone are however remarkably constant; it may indeed be said to be almost universal within this district; one exception, however, is afforded by Cross hill a little to the west of Fairhead, where the basalt overlies even these, and reposes immediately on the regular coal measures of the Ballycastle district.

The section presented at this point is also worthy of mention, on account of its general resemblance with that of a part of the Campsie hills, published by Col. Imrie in the Wernerian Soc. Trans. Vol. 2. The whole series may be examined with the greatest advantage in the neighbourhood of Belfast, where all its members occur.