Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/467

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457
Dr. Mac Culloch on Quartz Rock.

obvious that there is no provision made for this rock in Werner's classification, if I have succeeded in proving that it is as little entitled to the name of quartz, as to that of granite, and that it is not a purely primitive and chemical deposit. Its mechanical structure deprives it of a right to the latter title, and its connexions and disposition prevent us equally from arranging it with the latest stratified or “flœtz” rocks. If it is a necessary condition of the “transition” rocks to contain organic remains, then this rock is also excluded from the intermediate or transition class, as much by this as by its position in respect of the mica slate, universally esteemed among the primitive, or to speak more properly among the most ancient rocks.

Such are the inconveniences of artificial arrangements, whether they are groundless, or founded on partial views of natural productions. It has been proposed indeed to call this rock graywacke, a quartzose graywacke. But this is in fact to confound all distinctions for the sake of an adherence to a system, which may without disgrace admit a new member into any of its series, should it appear that a member hitherto unobserved does actually exist. The name graywacke has been already too much abused, and is become a fruitful source of confusion and error. It is incumbent on us to diminish instead of increasing this evil, by a more careful application at that, as well as of other geological terms, and by limiting its use within the rigid compass of definition. On that definition I need not now insist; nor will I attempt at present to assign the true place of the quartz rock in the general arrangement. It will be done with greater facility when I have described its connexions in the other places where I have observed it.

Vol. II.
3 m