78 MONOGRAPH OF DURA DEN. 



fined to these points alone. The dip, indination, and general 

 bearing of the strata are perfectly similar. " In the district 

 between Drumquin and Pettigo, we have the whole of the con- 

 stituent rocks of the carboniferous formation ; on the north the 

 Old Red Sandstone, succeeded on the south by the calciferous 

 slate and mountain limestone, and these again by the black 

 shale, all with regular dip and in regular succession ;"* the 

 beds dipping mostly south-east and at a small angle, and in 

 the same stratigraphical arrangement. The thickness of the 

 yellow rock at the top of the Old Red is represented from 

 50 to 100 feet in Sligo and Mayo ; in the King's and Queen's 

 counties, it is from 200 to 500 feet, and in Galway and Clare, 

 " the yellow colour prevails altogether, and the thickness of the 

 red beds near the base is only about fifty feet." 



The faults, dislocations, and intrusions of the igneous rocks 

 are, however, so numerous and deranging everywhere in the 

 Old Red and coal-field districts of Ireland, that any attempt to 

 work out the geology of any one of the systems by the succes- 

 sion and other peculiarities in the strata alone, is extremely 

 difficult, and perhaps scarcely practicable. The discovery of 

 organic remains, of the Dura Den type, would greatly facilitate 

 the solution of the points at issue, and I have little doubt, from 

 the large-scaled Holoptychius Portlochi found in the beds at 

 Cultra, that they may yet be detected in abundance in the 

 subjacent strata in the vicinity. Palceoniscus scales, and rays 

 and teeth of Gyracanthus, are everywhere abundant in the 

 ironstone shales in Fifeshire ; and a few miles to the eastward 

 of Dura Den, at Mount Melville near St. Andrews, large jaw- 

 bones with teeth of great size and in the most perfect state of 

 preservation, along with bright enamelled scales and other 

 relics, are very numerous. 



4. Have we evidence to determine whether these are marine 

 or lacustrine deposits, and of what aqueous habits were the 

 fishes under review 1 Professor Huxley, "On Cephalaspis and 



* Pji. 18, 21, fit passim. 



