5. The sandstone district, of which the lower beds are associated with the coal, and the upper with gypsum. The collieries are distinguished by black circles.
6. The zone formed by the basset of the chalk round the escarpments of the mountain groupe, which forms our third system. It was not possible to insert the lias and greensand intervening between the sandstone and chalk; but their localities are fully indicated in the paper and in the sections.
7. The great district of floetz trap.
The smaller map, Pl. 9, exhibits a general outline of the opposite points of Scotland and Ireland, intended to shew the connection between the principal formations in each country, as pointed out in the Introduction. The colours represent─1. Granite. 2. The mica slate district of the Grampians, and the northern chain in Ireland. 3. The transition district of the Lead hills in Scotland, and of Down in Ireland. 4. The secondary rocks associated in the coal district. 5. The floetz trap districts.
