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 upwai-ds, 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 enwi-aps the basalt. On the west side of the basalt is a 

 very hard rock resembling syenite, and M'hich 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 Cockbum Mill, a bed 

 of trap about 4 feet thick is seen overlying the old red sandstone strata for a con- 

 siderable extent. It is of a brown colom-, 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 

 Avith 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 laminae 

 contorted, shewing very clearly the effects of igneous action. As this bed of trap 

 appears to be destitute of augite, it should, minei'alogically, 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 Castlemains hill is a mass 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 800 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. dh-ection to Borthwick, and has upheaved at the 

 same time, both the felspathic rock and the more ancient sandstones. 



Borthwick hQl 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 



