1818.] Geological Transactions, Vols. III. and IV. 455 



quitting the interval between two given beds of limestone, or 

 sandstone, make its way across the one immediately above or 

 below, and then proceed with a regularity as great for another 

 long space between some other pair of proximate strata. In one 

 or more instances I have observed this to happen after more than 

 a mile in extent, throughout all which space not the minutest 

 irregularity had appeared to indicate any thing else than a 

 perfectly conformable and alternating stratification." 



The middle district of the island lying between the trap and 

 the stratified rocks already mentioned, contains the Cuchullin 

 hills, the most lofty and remarkable in their outline of any of the 

 mountain groups of Sky. The spiry forms of their summits, 

 their hard, serrated outline, the huge, and somewhat curvilinear 

 sheets of rock, that extend from their base to their summit, 

 almost unalterable by time and weather, and absolutely barren, 

 point out, even at a distance, that the rock of which they are 

 composed is very different from the surrounding and adjacent 

 trap and sienite. On a near inspection, it is found to consist 

 of hyperstene, in grains or crystals, mixed in some parts with 

 compact, green felspar, and in others with crystallized, white 

 felspar, somewhat glassy. 



3. On the Geological Features of the North-eastern Counties of 

 Ireland, extracted from the Notes of J. F. Berger, M.D. fyc. 

 with an Introduction and Remarks by the Rev. W. Conybeare. 

 Descriptive Notes, referring to the Outline of Sections presented 

 by a Part of the Coasts of Antrim and Derry, collected by the 

 Kev. W. Conybeare,with Observations by the Kev. W. Buckland, 

 Reader in Mineralogy to the University of Oxford. 



A right line drawn from Dundalk to Londonderry, and the 

 curve of the coast from Londonderry back again to Dundalk, 

 will include somewhat more than the district described in these 

 papers. It may be considered as composed of three systems of 

 mountains. Of these, one occupies the country lying south of 

 the Belfast River and Loch Neagh. The Mourne mountains are 

 its most elevated summits, and consist principally of granite. 

 Hornblende rock and primitive greenstone appear on the skirts 

 of the granite ; and at a greater distance from the central nucleus, 

 the greywacke formation is the prevailing rock. 



The second system has for its eastern boundary a line drawn 

 nearly N. and S. from the mouth of Loch Foyle to the parallel of 

 the northern extremity of Loch Neagh, and extends westward 

 to Donegal Bay, including the whole line of coast from Loch 

 Foyle to Donegal. This tract consists principally of mica slate. 



The third system occupies the whole country lying east of a 

 line drawn from the entrance of Loch Foyle to the southern 

 extremity of Loch Neagh. The prevailing rock in this district 

 is basalt ; but other rocks, from mica slate upwards to chalk, 

 make their appearance, especially on the coast ; and from their 

 various relations with the basalt, throw much light on the history 



