442 Dr. Mac Culloch on the Geology of 



All these beds are traversed by numerous veins of quartz, and 

 they alternate with each other wirhout any regular order, the beds 

 not forming a series passing from the coarse to the fine grained, but 

 a fine clay slate often following close upon a coarse graywacke, and 

 being succeeded by a similar rock. 



Here then we have an instance of a fact, of which the observa- 

 tions of every geologist will furnish many other examples, namely, 

 the occurrence of clay slate among those rocks called rocks of tran- 

 sition, their alternation rendering this part of the fact indisputable. 

 The nomenclature of rocks therefore which is derived from geolo- 

 gical situation, is here at variance with that which results from 

 mineralogical character. If the unnecessary multiplication of dis- 

 tinctions and names in mineralogical nomenclature is productive of 

 toil by introducing a cumbrous apparatus into the science, it has at 

 least the merit of conducing to accuracy of description. That is a 

 much worse extreme, which by rejecting all such distinctions con- 

 founds together under one sweeping term, all sorts of substances, 

 which, however differing in individual character and however con- 

 stant and uniform in the character each severally assumes, are 

 associated by only one common circumstance, the accidental one of 

 position. A mineralogical nomenclature, like that of the other 

 branches of natural history, must either be derived from the appear- 

 ances and properties of the individual species, or from the character 

 of the species combined with some generic or family character, either 

 natural or artificial, which may render it of more easy classification 

 and description. But we are not at liberty in the nomenclature of 

 mineralogy, to derive our terms sometimes from the appearance of 

 the species, and sometimes from the accidental circumstances which 

 are found to belong to it. This is to acknowledge two distinct 

 principles of nomenclature, and to claim a privilege of using that 



