SUPERIOR SANDSTONES. 419 



of division is sometimes extremely singular, but 

 as it cannot be rendered intelligible without a 

 figure, the reader must unavoidably be referred to 

 that work on the Western Island sal ready quoted, 

 where the most remarkable instance yet described 

 is represented. It is found in the Isle of Sky. 



Many singular modifications of a concre- 

 tionary structure, equally unintelligible without 

 drawings, occur in this rock ; and they are y in 

 the same way, detected only by the weathering 

 of the exposed surfaces. The consequences thus 

 produced, are often such as to resemble the artifi- 

 cial ornaments given by architects to rustic base- 

 ments ; the feebler parts wasting, while the 

 harder remain in a variety of hatched and vermi- 

 cular forms. 



The spheroidal concretionary structure on the 

 large scale, is sometimes found in these secondary 

 sandstones. In this case, the spheroids are inde- 

 pendent of each other, and imbedded in the ge- 

 neral mass ; being distinguished, after the wasting 

 of the surrounding parts, by their superior hard- 

 ness and permanence. The surfaces of these 

 spheroids are sometimes cracked into polygonal 



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