[27] See “Handbook to the Extinct Animals and Geological Illustrations described,” by Professor Owen.
The wonders of geology are not confined to grand mountain chains piercing the clouds, burning mountains vomiting steam and hot ashes, and vast accumulations of animal and vegetable remains found imbedded everywhere around us. They extend to facts connected with the structure of the earth’s crust, the existence of stores of mineral wealth, and strange results derived from the comparison of existing races with the fragments of other races formerly occupying the surface. The form of the surface depends on the internal structure; the scenery is due to the circumstances of the prevailing rock and soil; and the sea-cliff and naked mountain side are the places where nature teaches her first great lesson of the natural history of the Mineral Kingdom. To illustrate geology, it was necessary to perform the same kind of task as that which has been so successfully performed in the Architectural Courts, and the result is now before the visitor, as he looks down from this plateau and prepares to enter on the new course of investigation open to him. The ground forming the cliffs, shores, banks, and islands in this part of the Park are so constructed as to give, in a series of views, a number of practical lessons in geology, tending to make the essential facts of the science easily understood, while, at the same time, they add to the picturesque beauty of the scenery. The plan may be recognised in the fine expanse of cliff now at our feet; to do justice to which we must descend and place ourselves on the tongue of land below, or on the rustic bridge a little to the left. From hence may be seen the full length of the present cliff, and a few words of explanation will be sufficient to indicate the succession of rocks and the geological phenomena.
On this cliff, the part immediately facing the bridge represents a section nearly vertical of part of a coal-field, all the beds dipping (or inclining) at a moderate angle to the right-hand, so that those to the left are lower in geological position, though they gradually become higher in point of actual elevation, and at a little distance further to the left overtop the coal itself. Besides this illustration, we also see in the same equal part of the cliff instances of faults or troubles, throwing a part of the coal-measures into a different position from the rest, and lifting up portions of a series of deposits. In the case before us, the older rocks are also thrown up on the left side of the fault.
The coal-cliff consists of two beds or seams of coal, two of ironstone, and some sandstone. The part not consisting of projecting stone is supposed to represent softer rocks, clays, or shales. There are placed here about twenty-five tons of coal, twenty tons of grit or sandstone, and five tons of ironstone, all from the neighbourhood of Clay Cross.
In order to produce a marked contrast, the carboniferous limestone is placed next in order, and as if brought up to its position by a considerable fault. The millstone grit, appearing on the top of the plateau above the limestone, would have occupied naturally and without disturbance, a position below the lowest part of the coal measures. The fault is therefore called, technically, an upthrow or upcast to the south. The millstone grit consists of about 30 tons of rock from Crick, near Matlock, and from Bramley Fall quarries, in Yorkshire. The carboniferous limestone (of which there is 100 tons) is from the neighbourhood of Matlock, and is placed nearly in its natural position.
In this cliff of carboniferous limestone the bedding may be very distinctly traced, and systems of fissures, or joints, may also be observed. One of these fissures, wider than the rest and communicating with several smaller ones, is partly filled with spar, and has an opening into a cavern constructed behind the cliff. The main fissure represents a mineral vein or lode, and the smaller ones are strings or feeders. Within the cavern the spectator sees some of the peculiar and interesting appearances of natural limestone grottoes.
Coming out below the limestone, hard beds of the old red sandstone are seen. These have the same dip as the limestones, and are seen at intervals further to the left towards the railway. It is intended to continue the series of older and altered rocks in this direction. The old red sandstone on the ground consists of about twenty tons from near Bristol.
Overlying this whole series of old (or palæozoic) rocks, which are inclined to the north, is a horizontal, and therefore unconformable capping of new red sandstone. This also is from near Bristol, and the quantity provided was fifty tons.
The new red sandstone, thus capping the old rock on the high ground of the plateau, re-appears at the extremity of the nearest of the adjacent islands at a much lower level, and having a different mechanical position.
It is right to mention that these geological sketches are the result of careful consideration, and have not been effected without much constructive ingenuity. The original plan of the whole was suggested by Professor Ansted, and arranged with Sir Joseph Paxton at an early period of the laying out of the grounds; and as soon as the state of affairs permitted and the actual earthworks of the Plateau were in progress, a model of the intended structure was completed and coloured geologically by Professor Ansted. The works have been ably constructed from this model by Mr. James Campbell, who also procured the stone and other minerals from different parts of the country.