76 • MONOGEAPH OF DURA DEN. 



calciferous slate, those thirty being all taken from Mr. M'Coy's 

 determination of the specimens submitted to him. Seven of 

 those which I have noted out of the sixty-three, are of the 

 most common kinds found in the Irish carboniferous limestone 

 system." Instances of the same kind occur up and down 

 among all the systematic divisions, showing how Nature carries 

 forward her great progressional types with exceptional cases 

 in every epoch. 



But still, with all these interpolations in palseontological 

 reading, it is convenient to have resi)ect to lithological sub- 

 divisions, as already established on the greater scale of the 

 Silurian, Devonian, and carboniferous formations. Throughout 

 the great straths and valleys of Scotland the lines of demarca- 

 tion are generally well defined, and with no system of rocks 

 are they seen in finer relief than in those of the Old Red. 

 From the primary rocks of the Grampians to the Lomonds, 

 with successive anticlinal and synclinal dips, the outcrops of 

 every series are clearly traced ; the prevailing kinds of fossils 

 are persistent in the general suites of strata ; and, closing up 

 with the yellow sandstone of Dura Den, their mineralogical 

 characters all bear a family resemblance to one another, and to 

 the normal type of which the Devonian consists. The infinite 

 variety of mineral strata, especially, that build up the carboni- 

 ferous system ; the vast masses of lime, iron, and coal repeatedly 

 alternating with each other ; and the astonishing profusion of 

 details manifest in all the arrangements, are indicative of such 

 cosmical changes and conditions to which no former period of 

 the geological history of our globe bears any resemblance ; 

 and if Nature did from time to time cast oiF a few of her 

 typical specimens, and distribute them widely over sea and 

 land, as traced in the vertical superposition of the rocks, her 

 great divisional epochs, organic and inorganic, are not the less 

 strikingly marked and numbered. A remarkable class of 

 fishes, with a wide distribution and prohfic development, 

 characterizes the epoch of the Old Red Sandstone ; and from 



