44 MR STEVENSON ON THE GEOLOGY OF COCKBURNLAW, 
for about 300 yards farther down, wherever it has been protected from denuda- 
tion. It consists of a coarse sand (apparently triturated granite), containing 
rounded nodules of various sizes, from that of a pigeon’s egg upwards, formed of 
concentric coatings of the granitic sand round a nucleus, which appears to con- 
sist of an imperfect sort of basalt. 
The basalt is of a dark colour, approaching to black, and is very hard. It is 
occasionally amygdaloidal, and has a tendency to assume the form of concretionary 
masses of a spheroidal figure, consisting of concentric coatings. The granite is 
seen in contact with it on the north side,—the line of junction running in an 
ENE. direction. On the south side the two rocks are separated by a deep pool 
in the river, which has probably been formed by the washing out of the inco- 
herent tuff which here enwraps the basalt. On the west side of the basalt is a 
very hard rock resembling syenite, and which is probably greywacke, fused by 
the igneous rock. Its cleavages, as well as those of the granite and basalt, are 
ENE. by NNW. 
In the interesting section exposed by the Whiteadder at Cockburn Mill, a bed 
of trap about 4 feet thick is seen overlying the old red sandstone strata fora con- 
siderable extent. It is of a brown colour, and abounds in vesicles generally about 
the size of small peas, some of which are empty, but the majority are filled up with 
various minerals. Its texture is earthy, and it is much debased by being mixed 
with the debris of the adjacent sandstones and clays, portions of which it had taken 
up in its course when in a molten state. The embedded fragments are hard, 
crystalline, and cherty, and the adjoining strata are discoloured, and their laminze 
contorted, shewing very clearly the effects of igneous action. As this bed of trap 
appears to be destitute of augite, it should, mineralogically, be classed with the 
porphyries and other felspathic traps of the Lammermuirs. It is, however, more 
recent than these, having been erupted subsequent to the deposition of at least 
the greater part of the old red sandstones. At the same time, it seems to be more 
ancient than the augitic traps by which the second upheaval of the Lammermuirs 
was effected, as it shews some appearances of having participated in that move- 
ment along with the adjoining sandstones. 
The trap of Castlemams hill is amass of greenstone, which has forced its way 
through the old red sandstone strata. The sandstones are much hardened at and 
near their junction with the trap, while the same beds are seen within 300 yards 
to NW., in contact with, and tilted up by, the grey felspathic rock of the Knock hill, 
without the least appearance of alteration. The latter circumstance which seems 
rather anomalous, is accounted for by a dyke of augitic trap, which runs from 
under the Knock hill in a SSE. direction to Borthwick, and has upheaved at the 
same time, both the felspathic rock and the more ancient sandstones. 
Borthwick hill is a vast mass of basaltic greenstone, which has been erupted 
through the old red sandstone strata at the place of intersection of several fissures 
