American Association. 265 



are uiiconformably overlapped by those conglomerates and sand- 

 stones whicli form the very base of the Devonian loolcs or Old 

 Red Sandstone. 



That great series is clearly exhibited on the north east coast 

 of the Highlands, and is made up of three subdivisions; viz., (a) 

 Lower Conglomerates and Sandstone, (b) Middle Flagstones and 

 Schists, with abundance of the well known ichthyolites, and (c) 

 Overlying Sandstones — the latter constituting the northern head- 

 lands of Caithness, and the chief hills of the Orkney Islands. 



I feel confident that this triple series represents in full, as I 

 have endeavored to show in my work, Siluria, the Devonian rocks 

 of Devonshire, as well as the slaty rocks of the Rhenish Provinces 

 (including the Terrain Rhenan of Dumont.) 



The experimentum crucis as respects Russia, was in fact settled 

 by the discoveries of my colleagues De Verneuil, and Keyserling 

 and myself, when we found the fossil shells of Devonshire and of 

 the gorges of the Rhine, in the same beds with the ichthyolites of 

 the Scottish Old Red ; many species being identical. 



In turning to Ireland we have there obtained evidences illus- 

 trative of the conversion of Lower Silurian rocks, as shown by sec- 

 tions across the Connemarra Mountains, where a gi'eat succession 

 of crystalline limestone and quartzites, including the green Con- 

 nemarra Marble, having been observed to lie directly beneath 

 strata with fossils of the Llandovery Rocks (Middle Silurian), I 

 have had no hesitation in considering these altered masses to be 

 representatives of the Lower Silurian of other tracts. (See Siluria 

 p. 108.)* 



Again adverting to Ireland, the Survey under our friend Mr. 

 Beete Jukes has ascertained, that in the Dingle Promontory true 

 Upper Silurian Rocks, with both Wenlock and Ludlow fossils are 

 conformably surmounted by many thousand feet of hard chloritic 

 and silicious grits and schists (Glengarifi" grits), which represent 

 in my opinion the great mass of the Devonian Rocks. The pecu- 

 liarity, however, of the Irish section is that between these Glen- 

 gariff Grits, and that which has hitherto been exclusively called the 

 Old Red Sandstone of Ireland, there is a great hiatus ; for the lat- 

 ter reposes on the edges of the former, and passes conformably 

 under the carboniferous deposits. 



*NoTE. — I examined this tract last year in company with Mr. Jukes, 

 Mr. Griffith and Mr, Salter. Mr. Du Noyer has ably mapped and deline- 

 ated the country. 



D 



