Page:The Geologist, volume 5.djvu/112

88 tain limestone, as we continue our researches higher up in the beds we find their remains becoming more scanty, until at the top they are exceedingly rare. One bed is rich in zoophytes, another in goniatites, whilst another is composed of the broken fragments of Sanguinolaria, and the whole of the beds contain numbers of Spirifer imbricatus, which connects them like a huge bracket from top to bottom. Some rare geologizing may be had along the lower beds; almost every stroke of the hammer lays open something novel.

The remarkable fissures which occur in the limestone of Derbyshire have afforded matter of speculation to the curious for centuries; the most remarkable one is called the Winnats, and is about a mile distant from Castleton. It gives rise to the most sublime scenery, for the fissure is caused by the splitting of a hill in twain, and the steep precipices on either hand for the distance of a mile and a half, resemble the ruins of old towers and buttresses, in some places clad with ivy, and tenanted by bats and owls. Another such fissure is at the back of the town, and has been already referred to. In some places the passage at the bottom of this is not above three yards in width, and is much of a character, in other respects, with the Winnats. Much speculation has arisen as to the origin of these rents; they occur at nearly right angles to the line of strike, and have doubtless been formed in the first instance by the upheaval and desiccation of the rocks, thus:—

Subsequent to this they have been worn and channelled by atmospheric and aqueous action. They have been attributed to plutonic agency, but it needs little geological knowledge to see that the above theory is the true one. Along the lower beds in the Cave Dale there is another good spot or two for the geologist. Here are found numbers of trilobites, some quite entire; groups of the entomostracan Cytheræ, and that rare fossil the Cyclas radialis. One bed seems quite a nest of Pleurorhyncus armatus, although they are very fragile and require great care to extract them with the cone entire. Plutonic action has not been absent in the neighbourhood, for at the top of this fissure are beds of greenstone, and an imperfectly columnar basalt, whilst the limestone around seems to be somewhat crystallized by the heat to which it has been subjected by the intrusion.

Old Mam Tor, the "Shivering Mountain," in geological position lies just above the limestone. The shales which compose it are speedily decomposed by atmospheric agency, and hence have given rise to the popular name which the mountain bears. The inclination of its beds is E.N.E., and the intensity of their dip about 40°. These