396 Dr. Mac Culloch on the Geology of 



seen below It. The accompanying specimens will preclude the 

 necessity of describing a rock of no uncommon occurrence, whe- 

 ther the name by which I have designated it be one about which 

 mineralogists are agreed, or not. It has unfortunately been ap- 

 plied to so many different stones, that it is utterly impossible to 

 steer clear of difficulties. Among the reforms of nomenclature, 

 in the departments of rocks, the term hornstone, and the va- 

 rious substances which have been classed under it, call loudly for 

 examination. The adoption of petrosilex might have gone some 

 way to remove this confusion, as we should then have had two 

 names instead of one, by which to designate four or five different 

 substances ; but as this latter appellation has been equally misap- 

 plied with the former, and different authors have called the same 

 substance by both these names, the confusion has, if any thing, 

 been increased. Mineralogists may inquire whether by a due appro- 

 priation and limitation of the three terms, hornstone, chert, and 

 petrosilex, already in use, some progress may not be made in re- 

 moving this obscurity without any material additions to our no- 

 menclature. I forbear even to hint at the apparently, and only 

 apparently, corresponding French terms, pierre de corne, and 

 corneene, lest I should drive the reformer to despair. 



But to return. This bed dips to the south-west, and appears to 

 have about 15 degrees of elevation. Immediately above it lies a 

 bed of rock, about 20 feet in thickness, and of a structure so 

 peculiar as to require a more detailed description. 



It is formed of globules, every where adhering together, not 

 merely by their touching surfaces, like most of the pisolites, but in 

 general by large segments, similar to the globular limestone of 

 Sunderland. These are occasionally compressed as if by a super- 

 incumbent weight, but in many places are absolutely spherical, and 



