235 
Geological Relations of the East of Ireland. 
represents a portion about six feet long by four and a half feet wide, 
of a firm bed of greywacke; the former dimension being in the line 
of the range, and the latter of the dip. The veins a and b are of 
quartz, mostly of a nearly pure white colour, but some of the veins 
of a are partly spotted pale bluish grey. The veins 1, 2, and 3, 
are white spotted with pale bluish grey, and these veins consist 
partly of grey quartz, and partly of white calcareous spar, to which 
the two colours are chiefly to be ascribed ; but the grey seems partly 
to arise also from minutely disseminated galena and brown blende, 
both of which substances I have discovered in these veins, though in 
very minute and scarce portions. The broadest of the veins do not 
exceed two or three inches. Plate 13. fig. 7. represents a contempo- 
raneous vein of quartz in a fragment of greywacke, two feet long 
by one foot broad. It is an horizontal section. Plate 13. fig. 8. is 
a vertical section of the firm rock, fifteen feet long by six to seven 
feet high, exhibiting contemporaneous veins of quartz in grey- 
wacke. 
In contemplating these subjects, I think it scarcely possible to 
avoid the conclusion, that contemporaneous veins have originated jn 
fissures, consequent to the first stages of consolidation of the rocks 
in which they occur, and filled up by expression and infiltration 
from the consolidating mass. The facts, considered as supports to 
this opinion, are, 1 st, the analogy of composition between the veins 
and the contiguous rock ; 2nd, the adhesion to and incorporation of 
the veins with the rock itself ; and 3rd, the intersection of the veins 
by the seams which also traverse the rock. We may likewise 
remark, that the seams sometimes heave or dislocate the veins, and 
that these seams are sometimes empty, sometimes occupied by quartz 
or calcareous spar. 
The laws by which the operations of nature are governed are the 
2 g 2 
