34 MR STEVENSON ON THE GEOLOGY OF COCKBURNLAW, 
ganic origin; but as no trace of organic matter is observable in these specimens, 
it is uncertain whether they are not merely the effects of a chemical aggregation. 
2. The Old Red Sandstone. 
The formation which in this district immediately succeeds the greywacke, is 
the wpper division of the old red sandstone, there being no strata on the flanks of 
the Lammermuirs, referable to any of the intermediate formations, comprisingthe 
Silurian system, and the lower and middle divisions of the old red sandstone. The 
position of the red sandstones and conglomerates, with reference to the grey- 
wacke, is unconformable. This is very distinctly seen at Cockburn Mill, where 
the conglomerate, which constitutes the lowest member of the formation, is well 
exposed, overlying the fractured ends of the greywacke strata in such a manner 
that the planes of stratification of the two sets of rocks are nearly at right angles to 
each other. The greywacke strata here are of the red variety, and dip at high 
angles to NW., the vacancies between their uneven and broken ends being filled 
up by the conglomerate. The latter is chiefly composed of fragments of the sub- 
jacent red greywacke, together with pieces of the felspathic rocks of the Stane- 
shiel ; the whole being firmly cemented by the finer arenaceous particles derived 
from the adjoining rocks. 
The variations in the thickness of the conglomerate at different localities of 
this limited district are very great, and would appear to indicate the proximity 
of the shore, at the period of its deposition ; a view which other circumstances, to 
be hereafter detailed, tend strongly to corroborate. At Cockburn Mill, its thickness 
may average about 20 feet ; whereas to westward of the Knock hill, it is at least 
300 or 400 feet. At the latter place, it contains (besides fragments of greywacke, 
which are its chief ingredients) several varieties of felspar porphyry, together 
with rolled masses of quartz, hematite, and other minerals. In Kidshielhaugh, 
and near the Knock hill, it consists almost entirely of fragments of the felspathic 
rock, which occurs 77 situ at these places. These are cemented by calcareous spar, 
which has probably been derived from the igneous rock, as the latter contains a 
considerable quantity of carbonate of lime in its composition. Similar instances 
of calcareous matter acting as a cement to the conglomerate, are not unfrequent 
on the borders of the Lammermuirs. 
At Cockburn Mill, the conglomerate passes, by a series of alternating conglome- 
rates and sandstones, into the characteristic strata of the formation. These con- 
sist of red and greenish-white sandstones, which alternate with red clays, the 
thickness of the whole of which, as exposed in Prestonhaugh, is probably at least 
300 feet; but, on account of the shattered nature of the strata, this cannot be ex- 
actly ascertained. Much interest attaches to these strata on account of the orga- 
nic remains, and the curious markings which appear to be of organic origin, m 
which they abound. These we shall attempt to describe as concisely as possible. 
