Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/452

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Dr. Mac Culloch on the Geology of

All these beds are traversed by numerous veins of quartz, and they alternate with each other without any regular order, the beds not forming a series passing from the coarse to the fine grained, but a fine clay slate often following close upon a coarse graywacke, and being succeeded by a similar rock.

Here then we have an instance of a fact, of which the observations of every geologist will furnish many other examples, namely, the occurrence of clay slate among those rocks called rocks of transition, their alternation rendering this part of the fact indisputable. The nomenclature of rocks therefore which is derived from geological situation, is here at variance with that which results from mineralogical character. If the unnecessary multiplication of distinctions and names in mineralogical nomenclature is productive of toil by introducing a cumbrous apparatus into the science, it has at least the merit of conducing to accuracy of description. That is a much worse extreme, which by rejecting all such distinctions confounds together under one sweeping term, all sorts of substances, which, however differing in individual character and however constant and uniform in the character each severally assumes, are associated by only one common circumstance, the accidental one of position. A mineralogical nomenclature, like that of the other branches of natural history, must either be derived from the appearances and properties of the individual species, or from the character of the species combined with some generic or family character, either natural or artificial, which may render it of more easy classification and description. But we are not at liberty in the nomenclature of mineralogy, to derive our terms sometimes from the appearance of the species, and sometimes from the accidental circumstances which are found to belong to it. This is to acknowledge two distinct principles of nomenclature, and to claim a privilege of using that