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 greywacbe, is 

 the vpper 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- 

 wackc, 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, haematite, and other minerals. In Kidshielhaugh, 

 and near the Knock hill, it consists almost entirely of fragments of the felspathic 

 rock, which occurs in 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, in 

 which they abound. These we shall attempt to describe as concisely as possible. 



