OVER THE HILLS OF THE NORTH OF ENGLAND. 269
Its species, it will be noticed, belong, with very slight exception, to botli the Carboniferous and Sbite ranges. Tlie montane botany of the Por- pliyry is just tluit of the two moi'e southern ranges, with a large deduc- tion.
2. Remembering the lower altitude reached by the Oolitic range, its drier rocks and lower rainfall, it might naturally be expected to yield much fewer Montane plants than the other three masses, and this expec- tation is fulfilled. The most striking instances of plants frequent in the three other ranges and absent here, are furnished by Rnbns C^Kinicemoras, Epilobinin ah'nii folium, Sediun villosiim, Saxifraga stellaris and JnjpiioiJes, Hleracinm pallidum, and Curex rujida.
3. Of the twenty-four species that occur in the Slate mass, but are absent from the Carboniferous range, eiglit only may fairly be called frequent. These -eight are SiU'ne acanlis, Alchemilla olpina, Circcea alpina, Sednm Rhodiola, Lobelia Dortmanna, Oxi/ria reniforiiiis, Salix herbdcea, and Isoetes lacustris. Of these twenty-four species, three, — Sabularia aquatica. Lobelia Dortmanna, and Isoetes lacustris, — one rare, two common, grow submerged in the lakes ; one species only, Salix herbacea, belongs distinctly to the hill-peaks, which in this mass, out of the four only, reach the mid-arctic zone ; and ten species, — Arabis petrrsa, Lychnis alpina, Cerastiuni alpirmm, Saxifraga nivalis, S. oppositifoUa, Hieraciitm alpinum, H. pulmonarinm, Sauss/irea alpina, Luznla spicata, and Poa alpina, — are rare plants of the precipices of the Inferarctic zone, of which there are very few in the Carboniferous tract. The vertical and horizontal ubiquity of Allosorus crispus in the Slate tract is also a positive characteristic that should be taken into account, as one of its prominent botanico-geographical features ; and the ubiquity of Salix herbacea on its peaks of the Mid-arctic zone.
4. Although for the restriction of most of the twenty-four species to the Slate mass, which grow there but not in the Carboniferous tract, it is not difficult to find a plausible reason, it is not the same for the presence of the twenty-four species in the Carboniferous tract which are absent from the Slate, the names of which a glance at the table just given will show. For four of them, — Draba incana, Dryas octopetala, Orobanche rubra, and Sesleria crendea, — we may, no doubt, safely account on the score of a distinct preference for the limestone. But still twenty species remain, for the occurrence of which here, and not in the Slate hills, I cannot venture to allege any cause ; and the occurrence of these twenty species under such conditions seems one of the most curious problems which the geographical botany of the centre of the island offers for our solution. Of these twenty species, ten are restricted to Teesdale. Alt the twenty are mainly or entirely plants of the .Agrarian region, confined to, or with their head-quarters in, the Superagrarian zone. In addition to the presence of these species here which are absent from the Slate, the following, which are rare or very rare in the latter, are much more abundant in the eastern mass, viz. Thlaspi alpestre, Fiola Intea, Arenaria verna, Potentilla frnticosa, Rnbns Chamw morns, Sedum, villosnm, .ispleninni viride, and Eqnisetnni varieyatnm. I shoidd not omit, also, to mention the abundance of Gentiana verna in Teesdale, in contrast with its absence from the Slate in this connection, although standing as an " Intermediate" in the ' Cybcle,' it has not been included in my catalogue. The ubiquity of Rnbns C.'hamamorns on the Inferarctic Carboniferous peaks is also a salient character of contract.