298 Scientific Proceedings, Royal Dublin Society. 



are Trias rocks ; and in places Cretaceous rocks (White Limestone),, 

 Eocene (?) Doleryte, and the " Lough Neagh beds " — the age of 

 the last being still disputed. 



Associated with the Metamorphic rocks are Granitic rocks of 

 three or more distinct ages. In the westward and north-west- 

 ward there are other tracts of Carboniferous rocks. 



In the south of the county the Carboniferous rocks have well 

 marked divisions, having a Central zone of sandstones and shales 

 (Calp), while to the westward and north-westward they are more 

 mixed up. The Calp of Ulster is more or less similar to the Coal 

 Measure sandstones and shales, having in it, in the Co. Derry, 

 workable beds of clay-iron-stone ; and at Bally castle, Co. Antrim, 

 workable coals. By some observers the rocks of these two distinct 

 groups have been confounded together. This is a matter of im- 

 portance, as this incorrect mapping has led persons to make 

 unsuccessful trials for coal in the Calp. 



In the Silurian are the characteristic felspathic bedded rocks 

 (eurytes) ; while associated with the Trias, in the north of the 

 county, are dolomytes, said to contain fossils of Permian types. 



In the " Lough Neagh beds " are seams of lignite, but too 

 insignificant to be valuable ; silicious pieces of the lignite are 

 known as " Lough Neagh hones." 



In the Trias at Croagh, also elsewhere, gypsum has been 

 found, but not in sufficient quantity to be economically worked. 



The Tyrone coals are seemingly of great importance. As has 

 already been mentioned, the coals in Leinster and Munster are in 

 the Upper Measures, and those in the Connaught field in the 

 Middle Measures ; but in Tyrone they are found both in the 

 Middle and Tipper Measures. Furthermore, the Ulster are gas 

 coals, while those of Leinster and Munster are anthracates ; those 

 of the Connaught field seem to be intermediate between both. 

 The extent of the coal-field is unknown ; for although the coal 

 ^.t the margins of the exposed field must extend under the adjoin- 

 ing younger rocks, this extension has never been proved by either 

 borings or sinkings. 



The coals at Drutnglass, near Dungannon, in the Middle- 

 Measures, have had their exact height above the Limestone proved 

 by a series of bore-holes ; but their extent is unknown, as it i& 

 still an open question whether they extend under the whole or 

 only a part of the field. 



