Dr. Mac Culloch ott Qtiartz Rock. 461 



stance highly instructive with regard to the composition of many 

 other rocks. Of these natural analyses, a very common one is the 

 appearance of laminas of red and white matter, alternating either in 

 fiat plates, or in that peculiar undulating form so well known in the 

 Jloetz sandstones, and marking the action of water on loose sand. 

 An occurrence of equal importance and greater singularity is that of 

 imbedded cylindrical bodies which they occasionally exhibit. I may 

 previously remark that they have a frequent tendency to break into 

 rectangular solid masses, similar to those which occur in many floetz 

 sandstones. In these fragments the weathered surfaces present on 

 the upper part, or that which forms the plane of the stratification, a 

 number of circular protuberant spots, apparently arising from the 

 circumstance of their hardness being greater than that of the general 

 mass. The lateral plane of the same fragments exhibits on the 

 other hand a similar number of corresponding cylinders, of a hard- 

 ness in the same way superior to that of the surrounding parts. If 

 I might venture on a comparison as vulgar as it is explanatory of 

 this appearance, I would compare it to the two sections of a piece 

 of larded meat. I may further add, that in these cases the cylindrical 

 bodies are of a much whiter colour, as well as of a more compact 

 texture than the rest of the stone ; and that on breaking the stone to 

 examine further into this structure, the whole disappears, and an 

 uniformity of texture is exhibited throughout. 



This peculiar appearance is familiar to all those who are conversant 

 in the varieties oi f.oet'z sandstone, and the superior hardness of the 

 cylindrical or vermicular bodies in the sandstones of this class is 

 equally notorious, as they often continue to project for the space of 

 even half an inch beyond the decomposing rock, appearing as if 

 nails had been driven into it. The coast of Fife about Burnt Island 

 affords excellent examples of this fact. I know not that any attempt 



