Page:Transactions of the Provincial Medical and Surgical Association, volume 2.djvu/195

 a short distance below Weston-Super-mare. The rock of which it is composed, may be seen, also, in the Holm Islands, which lie in the channel nearly opposite to Weston. Those who have the slightest knowledge of geology, will not need to be reminded that while the mountain or carboniferous limestone forms the outer shell, as it were, of a coal basin, it is lined within by the rock called millstone grit, immediately upon which the other coal measures are arranged, consisting, in this district, of lower coal shale, pennant, and upper coal shale. Over these inclined strata lie the horizontal beds of dolomitic conglomerate, new red sand-stone, and lias; and, according as the latter have been removed by various denuding agents or convulsions, the former are exposed. On taking a survey of the tract of country immediately surrounding Bristol, we observe an irregular plain, bounded to the west by the mountain limestone and millstone grit, to the north by the lias, to the north-east and east by pennant, and to the south by lias again. The basis of this plain is composed of red marl and new red sandstone. We shall speak more particularly of the soil which covers it, after describing the city and suburbs in relation to this and the other rocks.

The highest and most picturesque parts of Clifton are on the mountain limestone. This rock extends along the defile of the Avon on both sides, constituting, on the northern bank, St. Vincent's Rock, and after an interruption of dolomitic conglomerate, of small extent, stretching over Durdham-down, and on to Cook's Folly, below which it is seen to rest on the old red sandstone. On the cliffs formed by this