Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/406

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Dr. Mac Culloch on the Geology of

seen below it. The accompanying specimens will preclude the necessity of describing a rock of no uncommon occurrence, whether the name by which I have designated it be one about which mineralogists are agreed, or not. It has unfortunately been applied to so many different stones, that it is utterly impossible to steer clear of difficulties. Among the reforms of nomenclature, in the departments of rocks, the term hornstone, and the various substances which have been classed under it, call loudly for examination. The adoption of petrosilex might have gone some way to remove this confusion, as we should then have had two names instead of one, by which to designate four or five different substances; but as this latter appellation has been equally misapplied with the former, and different authors have called the same substance by both these names, the confusion has, if any thing, been increased. Mineralogists may inquire whether by a due appropriation and limitation of the three terms, hornstone, chert, and petrosilex, already in use, some progress may not be made in removing this obscurity without any material additions to our nomenclature. I forbear even to hint at the apparently, and only apparently, corresponding French terms, pierre de corne, and cornèene, lest I should drive the reformer to despair.

But to return. This bed dips to the south-west, and appears to have about 15 degrees of elevation. Immediately above it lies a bed of rock, about 20 feet in thickness, and of a structure so peculiar as to require a more detailed description.

It is formed of globules, every where adhering together, not merely by their touching surfaces, like most of the pisolites, but in general by large segments, similar to the globular limestone of Sunderland. These are occasionally compressed as if by a superincumbent weight, but in many places are absolutely spherical, and