KORTHUMBEKLAND AXD DURHAM. 39 



oppositifoliuin, Montiafontana, and Stellaria uliginosa growinter- 

 mixed, and in the swamp by the stream side are Carex dioica., 

 stellulata, p^dicaris, flava, and glauca, Molinia cmnilea, and yel- 

 lowish-green soft glossy tufts of Pinguicula. The drier and more 

 grassy parts of the hill-side yield Galium saxatile, Triodia, An- 

 tlwxantlium, Carex hinervis, Potentilla tormentilla^ and abundance 

 of Festuca ovina. The highest ridge is formed of large rounded 

 crags of a coarser-grained rock than the scattered masses below, 

 often variegated with lichens, obscure-crusted black-pointed Le- 

 cidecB, interspersed sometimes with the brighter hues of Lecidea 

 geograpliica, wide - spreading silvery -grey patches of Cetraria 

 glauca and Parmelia saxatilis, and darker ones of the omphalodes 

 variety of the latter, coral-like cushions of Sphcerophoron, and 

 the ink-coloured leathery thallus of Umlilicaria proloscidea. The 

 crags are too dry to produce many mosses, the priacipal kinds 

 which occur being Sypnum cupressiforme and Dicranum scoparium 

 upon their exposed faces, and in the shady crevices Jungermannia 

 albicans and Mnium hornum. In the sheltered hollows Lastrea 

 dilatata may sometimes be seen and Lu%ula syhatica amongst the 

 scattered ling bushes, and casually Listera cordata and Vaccinium 

 vitis-idcea under the shade of the heather. 



This, then, is the kind of vegetation which, with extremely 

 little variety, covers a large proportion of the uncultivated and 

 especially the upland parts of our two counties. The most dis- 

 tinctly marked influence upon the topography of the species 

 produced by the distribution of the subjacent rocks, is the more 

 or less absolute restriction of a certain number to the limestone 

 tracts. Out of our eight hundred and forty-four native species 

 there are forty-four which show clearly this lithological restric- 

 tion. In jSTorth Yorkshire, as might be expected from the greater 

 predominance of the calcareous element in the strata, the number 

 of these Xeropliilous, or dry-loving species, as Thurmann calls 

 them, is considerably greater. There are three tracts of lime- 

 stone in the Forth Eiding, the Carboniferous, Permian, and 

 Oolitic, which are surrounded by, and separated from, one ano- 

 ther by wide tracts underlaid by arenaceous and argillaceous beds, 

 so that it is a district exceedingly well -adapted for showing 



