198 SERPENTINE. 



tion, there is too often an hypothesis which vitiates 

 the observations. But, in our own country, it pre- 

 sents very few instances of a form, even approaching 

 to this. Most of the smaller, and even some of the 

 larger, examples, are shapeless masses, or irregular 

 nodules, if that term may be applied to bodies of large 

 dimensions. In this respect, however, Serpentine is 

 somewhat analogous to limestone; since among the 

 primary ones, irregular masses are not uncommon. 

 Limestone is, in fact, occasionally entitled to be consi- 

 dered unstratified, as much as Serpentine; but it must 

 be remembered that it does not form veins, except as 

 calcareous spar, and that it has no proper transition 

 into other rocks. 



The masses of Serpentine vary in dimensions, from 

 a mean diameter of even a few inches to one of miles; 

 though in the latter, a more perfect examination than 

 the ground will often afford, might discover traces of 

 stratification not visible on a general view. This is 

 the case in Unst; where, throughout a very extensive 

 tract, no marks of the stratified disposition can be traced, 

 while in other places, it is perfectly distinguishable. 

 At Portsoy and in Sutherland, it occurs in a form par- 

 taking both of the nature of a stratum and of an ir- 

 regular mass ; as happens in the primary limestones. 

 Such bodies are included among other strata; and, 

 for a certain space, at least, they have two flat and 

 somewhat parallel sides, determined by those of the 

 including rocks, but which soon converge in every 

 direction, so that the mass becomes extenuated all 

 round till it vanishes. If, in Unst, the stratified dis- 

 position is often imperceptible, it may arise from the 

 imperfect view obtained, in consequence of the nature 

 of the surface, and from the irregular manner in 

 which it is fissured : whence the divisions of the 



