DR THOMSON ON THE STRATA OF BERWICKSHTRB. 87 



at no great distance to tlie westward, in the direction of Coldstream, 

 the schistose and calcareous sandstones, which frequently accompany 

 the Berwickshire sandstone, make their appearance, and continue, 

 with little change, to the point at Birgham where I have ah-eady 

 described them as lying over magnesian limestone. The difficulty is 

 to determine how these strata are situated in relation to each other. 

 It is evident that they are closely connected : but we ask, is the 

 position of the sandstone above, below, or collateral with the carboni- 

 ferous rocks ? I have stated the reasons which induced me to class it 

 with the new red sandstone. No argument can sufficiently controvert 

 my statements, except observations on the rocks in. situ demonstrating 

 the contrary. Such I hold to be the experimentum cruets. 



The western boundary of the North Durham coal-beds is indicated 

 by the course of the river Till. For a little to the west of Duddo they 

 may be seen cropping out, and dipping from south-west to north-east. 

 I have examined the strata in this neiglibourhood, and am happy to 

 be able to add to the interest of this coal tract, by presenting a section 

 of the new shaft at Greenlaw-wells, which was commenced in 1832. 

 For this I am indebted to the attention of the son of the late intelligent 

 overseer, in company with both of whom, and one of the proprietors 

 (Mr Young) I descended on the 8th of November 1833. Although 

 the observations which follow are few, and perhaps of little moment 

 in so far as theory is concerned, still I think they are suffi.ciently im- 

 portant to require a place in the Transactions of our Club, because 

 they are facts, and facts are eternal. The shaft is about 31^ fathoms 

 in depth ; the section presented by it, being that of varieties of sand- 

 stone and shale, of various extent and thickness. Over the coal which 

 is worked, situated at the depth of 27 fathoms, lies a black limestone, 

 which is also observed underneath it. Above the limestone which is 

 situated over the coal, there is a stratum of shale, or tills, as the work- 

 men denominate it, filled with impressions of palm-like plants and 

 bivalve shells. In some places the superjacent limestone is absent, 

 and the shale occupies its place ; and as it forms the roof of the 

 level or drift, as it is termed, the fossil vegetables can be seen to great 

 advantage. 



The whole series dips at an angle of 45°, in a north-easterly direction. 

 Hence it is obvious that the coal would soon disappear, and attain 

 such a depth as to render its being worked a matter of impossibility. 

 Yet coal is raised in four or five places, in a line from Duddo to the 

 sea. The Cooper-eye coal, which is worked at Greenlaw-wells, is 

 understood to prevail in each of these localities, and therefore it must 

 be raised or brought nearer the surface in many points. This is 

 rendered more probable, when we consider that there is an extensive 

 trap-dike running from the Till to the sea, which may have been the 

 instrument in producing the extraordinary convulsion in this carboni- 

 ferous series in the neighbourhood of the Tweed. 



