Wright— Palceosoic Floor of North-East Ireland. 639 



Course of the Bann Valley Syncline. 



As regards the course of the intervening syncline, we have a fair amount 

 ol evidence. It may be regarded as embracing on the northern coast the 

 stretch between Downhill and White Park Bay, throughout which the chalk 

 is at or below sea-level. The western limit is defined by the line of high 

 hills of basalt stretching south by east from Magilligan, alonu' the western 

 escarpment of which the chalk occurs at heights of over 1000 feet. This is 

 also the direction of the valley of the Bann, and appears to be the direction 

 of the synclinal axis in this portion of the basalt plateau. The limits are 

 next defined by the north-eastern schist hills of Coolcoscreaghan and 

 Moneyoran. South of these the course of the trough seems to swing south 

 towards the northern end of Lough Neagh ; and its western limit is here 

 well defined by the elevated outlier of chalk on the summit of Slieve Gallion. 

 The relatively low-lying chalk of Moneymore is to be regarded as lying 

 within the trough. 



The actual lake basin itself, being probably due to epiite late subsidence 

 along the line of the syncline, helps to 'indicate by its outline the actual 

 course of the latter, which here runs first due south and then a little west of 

 south. This is true whether we consider the present lake or its former 

 extension as indicated by the clays. Finally, this westward deflection of the 

 syncline is confirmed by the series of lobes and outliers of Basalt, Trias and 

 Permian preserved in it, and extending over the Carboniferous and Silurian 

 Bocks towards Caledon, Armagh, Markethill, and Poyntz Pass. The form 

 and trend of the most southerly of these outliers indicate a return to a 

 direction slightly east of south in crossing the Silurian axis. 



Existence of the Transverse Trough in Pre-Mesosoic Times. 



We have up to the present spoken of the transverse syncline mainly as 

 affecting the Mesozoic and Tertiary rocks. It must, of course, affect to an 

 equal extent the Palaeozoic strata beneath. To be assured of the existence 

 of a coal basin beneath, we want something more than this. We need, in 

 fact, to know that the post-Tertiary folding and faulting along this axis are 

 only the last manifestations of more pronounced folding in pre-Mesozoie times. 

 Without evidence to this effect we would still have a presumption in our 

 favour; but with it we attain to a very high degree of probability. 

 Fortunately such evidence is forthcoming. Along the whole western margin 

 of the basalt plateau the effect of the Bann Valley syncline on the 

 Carboniferous strata can be clearly seen. They are brought in by both dip 

 and faulting in the direction of this axis of depression. The dip of the Lower 



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