Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/472

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Dr. Mac Culloch on Quartz Rock.

has been made to explain this circumstance in the flœtz sandstones, but it probably arises from the remains of some animal, a Sabella, or other marine worm. Whatever it be, it is sufficient to establish the similarity in the original structure of this mountain rock, with that of the present flœtz formation. I am the more particular in calling the attention of the Society to these resemblances, because I am unable to produce such decided instances of rolled pebbles as I have described in the rock of Jura, and am therefore apprehensive that the arguments by which I would prove the recomposed structure of this rock, may not appear sufficiently conclusive. But I have little doubt that many instances even of this occurrence, will be found by those who may have more time to bestow on the investigation, and who with better fortune may collect such specimens as might easily have eluded my cursory search. Proofs however are not wanting of mechanical attrition in the component parts of many beds of this rock, although the fragments do not absolutely reach the size of a pebble. A rock resembling ferruginous sandstone, of a highly compacted nature, is found in beds, alternating with the finer and more compact quartz rock, the grains of sand and gravel bearing most evident marks of attrition; and the whole mass being indurated to such a degree, that a hammer makes no more impression on it than it would on a mass of iron. It is still more satisfactory to find in certain positions, strata of absolute and perfect breccia, similar in aspect to those which now alternate with our older flœtz sandstones, but possessing the same extraordinary degree of hardness which I have just noticed. If there are any marks of organic remains in this rock less equivocal than the vermicular structure which I have described above, I did not see them, nor do I consider them necessary to establish its character, since our oldest flœtz sandstones are equally destitute of them. Under all these circumstances both of position