462 Dr. Mac Culloch on Quart% Rock. 



has been made to explain this circumstance in the fioet% 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 floetz 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 j^&^Z^ 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 floetz sandstones are equally 

 destitute of them. Under all these circumstances both of position 



