Geological Relations of the East of Ireland \ 197 
formations : for these are characters common to all classes of rocks, 
in a greater or less degree. And in the case before us, we have seen 
that the rocks in question are connected by insensible gradations 
with mica slate, and even with the fundamental granite itself,* 
Metalliferous Relations of the Eastern Mountain Chain • 
§ 89. The Eastern Mountain Chain, the leading features of which 
we have now examined, is remarkable in one respect, — the total 
absence of metals on the western side of the granite region, while an 
abundance of them exists on the eastern. The metallic repositories, 
found in the latter, I shall consider in two divisions, founded upon 
natural distinctions; those in the granite and mica slate tracts appear- 
ing in the form of true veins, with a single instance of a metalliferous 
bed: and the clay slate tract containing only beds and contemporaneous 
* Sau&ure, in his Agenda, chap. xv. No. 16, asks u Est-il bien constate, comine j’ai 
cru le voir dans les Alpes, qu’il existe des poudingues on gr&s, sinon primitifs, du moins 
d’une formation anterieure a celle de toutes les autres pierres secondaires?” If any 
doubt as to this point could remain in the mind of the reader, after an attentive perusal 
of the engaging and instructive Voyages dans les Alpes , it must be removed by the 
researches of later observers in the same regions, as well as in distant quarters of the 
earth; particularly by those of Von Buch. But it has unfortunately been the fashion, 
both on the Continent and in the British Isles, to designate the rocks of a particular 
tract by the name of transition , whenever any of the component members happen to pos- 
sess characters indicative of a mechanical origin, although in all other respects coinciding 
with those belonging to the primary class; and it is this practice that I deprecate, as 
tending to confound things otherwise distinct. Werner, the great founder of Geology as 
a science, certainly generalized too rapidly, when he excluded all mechanical agency in 
the production of primary rocks ; for though the general rule be true, that primary 
formations are of chemical origin, numerous exceptions undoubtedly occur, in which the 
effects of mechanical disturbance are plainly to be descried: as, ©n the other hand, 
secondary formations, though commonly possessing prominent and unequivocal marks of 
mechanical origin, are not unfrequently accompanied by such as are simply the results 
©f chemical affinity. 
