144 Professor Jameson m comucting Veins. 
II.— V EINS WHICH CONNECT MINERAL BedS TOGETHER, NOT 
CONFINED TO TrAP-ROCKS. 
In countries where trap-rocks abound, we sometimes observe 
in two beds of greenstone which are separated from each other 
bj strata of sandstone, slate-clay, limestone, or other rocks, 
that they are connected by means of veins that shoot from the 
floor of one bed into the roof of the other. The Fig. 4. Plate 
III., represents such an appearance ; a a, the beds of greenstone, 
c c, strata of limestone, and a; the connecting vein of greenstone. 
This arrangement is said to be peculiar to rocks which have 
been projected from below in a melted form, and hence Volcan- 
ists, I presume, would confine it to trap-rocks, as all of these are 
with them lavas. But this neighbourhood, so rich in illustra- 
tions of many contested points in geology, affords us examples 
of rocks, not of the trap series, with communicating veins. 
Salisbury Craigs, one of our most interesting hills, .is a mass of 
sandstone with subordinate beds of greenstone, and occasional 
layers of limestone, slate-clay, and clay-ironstone. On the 
south-east angle of the hill, in one of the quarries at present 
working, the following arrangement is to be observed. Green- 
stone, the uppermost stratum ; immediately below it a bed of 
coarse siliceous limestone ; under the limestone a bed of greenish- 
grey slate-clay ; and below the clay, strata of sandstone. Seve- 
ral veins of siliceous limestone shoot from the floor or under 
side of the bed across the slate-clay, and form a continuous 
mass with the floor or upper side of the sandstone ; and veins 
sboot from the i^oof of the bed of sandstone across the slate- 
clay into the floor of the siliceous limestone, and form with 
it a continuous mass. In other parts of the same quarry, 
branches or veins are observed shooting from the roof of the 
sandstone, and gradually terminating in the bed of slate-clay. 
These appearances are represented by the plan. Fig. 5., a, green- 
stone ; 6, siliceous limestone ; c, slate-clay ; d, sandstone ; 
c, veins shooting from limestone across the slate-clay into the 
sandstone ; veins shooting from sandstone across the slate- 
clay into the limestone ; and g, veins shooting from the sand- 
stone, and terminating in the slate-clay. 
