408 



The principal passes are at Colloony, Lough Talt, and Foxford. The 

 formations of which the mountains consist are mica-slate, hornblende- 

 slate, and quartz rock. Their bases are covered by a conglomerate 

 which the author considers to be the representative of the old red 

 sandstone; and on itreposes alternating strata of sandstone, andshale, 

 succeeded by carboniferous limestone. On the south of the chain 

 the limestone stretches towards Roscommon and Gal way, joining the 

 great limestone field of Ireland ; and on the N.W. it forms a plain, 

 extending from Sligo to the barony of Erris, where the Nephin group 

 rises from beneath it, being the commencement of the primary tract 

 reaching northward and westward to the ocean. Immense ridges of 

 water-worn pebbles occur in every portion of the district. *The coast 

 presents for the greater part bold, abrupt precipices, formed of gneiss, 

 mica-slate, quartz-rock, and mountain limestone ; but in some places 

 it is low, and composed of a succession of sand hills. 



II. In describing the formations comprising the district, the 

 author arranges them in the following descending order, — Carbo- 

 niferous limestone with beds of oolite, calcareous shale and grit, 

 old red sandstone or conglomerate, quartz-rock, gneiss, mica-slate 

 hornblende-slate, granite, trap-rocks, porphyry, and basalt. 



1. Carboniferous limestone tvith beds of oolite. — This is the pre- 

 vailing rock on the north and south sides of the Ox mountains. Ben- 

 bulben, 1700 feet, Knocknodie, 1025, and Knocknashee, 980 feet 

 high, are entirely composed of it. The lower beds contain black 

 chert, in angular nodules, and it frequently invests the organic re- 

 mains. The limestone varies in texture from compact to crystalline, 

 and in colour from grey to greyish brown. Arragonite, fluor spar, 

 brown spar, pyrites, and quartz crystals are sometimes found in it. 

 The mineral veins have been almost entirely neglected, only one near 

 Ballisadere, containing galenaand blende, having been wrought. The 

 organic remains are numerous, the principal genera being Caryo- 

 phyllia, Productus, and Spirifer. In the hill of Skreen, among the 

 lower beds, are thin layers of quartz pebbles, cemented by lime; 

 but beneath them are other strata without pebbles. 



The oolitic strata occur only between Moyne and Rathrea, 

 and are stated to lie below the limestone. They afford a durable 

 building material, take a tolerable polish, and contain comminuted 

 fragments of marine exuviae, and also (though rarely) carbonized 

 vegetable remains. Nodules of black shale, inclosing particles of 

 pitch coal, are likewise found in these strata, and between the beds 

 are partings of brown shale. 



2. Calcareous grit and shale. — This formation succeeds immedi- 

 ately either the carboniferous limestone or the oolitic strata, and 

 graduates at its lower extremity, where the conglomerate is wanting, 

 into quartz-rock; but it is stated that atGlenlassera the position of the 

 calcareous grit and the quartz-rock is unconformable to each other. 

 Sectional lists are given, to show the order in which the grit and 

 shale are associated ; and from one of these lists it appears that beds 

 of limestone are connected with them. The surface of the sandy 

 strata in some of the quarries presents waved ripple-marks. 



3. Old red sandstone. — This term is applied to the conglomerate 



