RAMBLES OF A GEOLOGIST. 425 



in no respect a different stone from what it is now. The 

 widely-spread Conglomerate base of the Old Red Sandstone, 

 which presents, over an area of so many thousand square 

 miles, such an identity of character, that specimens taken 

 from the neighbourhood of Lerwick, in Shetland, can scarce 

 be distinguished from specimens detached from the hills which 

 rise over the Great Caledonian Valley, contains in various 

 places, as under the Northern Sutor, for instance, and along 

 the shores of Navity, fragments of rock which have not been 

 detected in situ in the districts in which they occur as agglo- 

 merated pebbles. In general, however, we find it composed 

 of the debris of those very granites and gneisses which, as in 

 the case of the granitic axis here, were forced through it, 

 and through the overlying deposits, by deep-seated convul- 

 sions, long posterior in date to its formation. It appears to 

 have been formed in a vast oceanic basin of primary rock, 

 a Palaeozoic Hudson's or Baffin's Bay, partially surrounded, 

 mayhap, by bare primary continents, swept by numerous 

 streams, rapid and headlong, and charged with the broken 

 debris of the inhospitable regions which they drained. The 

 graptolite-bearing grauwacke of Banffshire seems to have been 

 the only fossiliferous rock that occurred throughout the en- 

 tire extent of this ancient northern basin. The Conglomerate 

 of Orkney, like that of Moray and Ross, varies from fifty to 

 a hundred yards in thickness. It is not overlaid in this sec- 

 tion by the thick bed of coarse-grained sandstone, so well- 

 marked a member of the formation at Cromarty, Nigg, and 

 Gramrie, and along the northern shores of the Beauly Frith ; 

 but at once passes into those gray bituminous flagstones so 

 immensely developed in Caithness and the Orkneys. I traced 

 the formation upwards this evening, walking along the edges 

 of the upheaved strata, from where the Conglomerate leans 

 against the granite, till where it merges into the gray flag- 

 stones, and then pursued these from older and lower to newer 



