PROFESSOR HEDDLE ON THE MINERALOGY OF SCOTLAND. 3 
jt invariably presents itself in larger crystals than those which are present 
in the general mass of the rock; and it would also appear to be present in 
these veins in a greater total relative amount than in the parent rock itself. 
This, should it be so, is not altogether difficult of explanation, if we are entitled 
to regard the rock as the parent of the vein. 
To the granitic belts of metamorphic rocks, and the intrusive granitic dykes 
of all rocks, such a term of relationship could only be very indirectly applied ; 
but to the exfiltrative veins of granitic rocks themselves, there is every reason 
to believe that the word fittingly applies. 
Such veins, in the old terminology of the science, were called contempora- 
neous,—a word somewhat puzzling in its application, and misleading at the best. 
A disquisition by Professor JAMESON on these “ contemporaneous veins ” 
forms the first of the publications of the Wernerian Society. 
It would appear to have been JAMESON’s purpose to show the distinction 
between these veins and what we would now call metallic lodes ; though it is 
not altogether clear that his description would not in some respect include 
injected veins therewith. 
He thus defines them :— 
“1, True veins traverse different strata, and are confined to single beds or strata only in those 
cases where the strata are of uncommon thickness. Their direction is not tortuous, and they 
seldom give off many branches. The mass of the vein is generally distinctly separated from 
its walls: it is frequently disposed in beds or layers, and these are parallel with the walls of 
the vein. The beds of these veins are so arranged that the newer beds are contained in the 
older. They often contain fragments which lie promiscuously, and are either acute angular, 
blunt angular, or rounded. Lastly, the materials of true veins are more or less different from 
the rock which they traverse, and the same vein contains several formations. 
“2. Contemporaneous veins.—Their course is tortuous, and they give off numerous branches. 
The mass of the vein is generally intimately mixed with, and passes into that of its walls, and 
differs but little in its component parts from that of the rock which it traverses. They never 
contain more than one formation, and when they contain apparent fragments the structure of 
these is ever conformable to that of the contiguous rock. Lastly, they traverse but single beds 
and strata, and are observed to wedge out in every direction, and consequently have no out- 
going above, below, or laterally, intimating that they have not been filled from above or below, 
but are as it were a secretion from the rock itself.” 
The above, so far as it goes, is an admirable description of exfiltrative veins, 
but it hardly sufficiently draws a line of demarcation between them and injected 
veins ; while the illustrations which JAMESON supplies show unmistakably that 
he had confounded exfiltrative veins both with injected veins and with the 
granitic and other bands or belts of rocks. 
Such bands in gneiss are instanced as illustrations, as are also the quartzose 
and micaceous bands of mica slate ; and these are placed in the same category 
with the “ veins of calespar which traverse transition-limestone.” 
