Page:Transactions of the Natural History Society of Northumberland, Durham, and Newcastle-upon-Tyne (1867).djvu/59

Rh in saying, 1.—The species which in Central Europe are restricted to dysgeogenous tracts occur with us in small number only, and are restricted lithologically in a similar manner. 2.—The species which in Central Europe are restricted to eugeogenous tracts occur with us in large number; and under our more boreal and humid climate grow abundantly, and cover wide areas of surface without keeping up any clearly-marked role of lithological restriction. And this shows us in what direction the interference of the rocks operates. A more porous and more humid soil evidently, to some extent, compensates for a drier climate; and in proportion as the climate is damper the characteristically dry-loving species are more restricted to dry-soiled tracts of country. This is the rule, and in botanico-geographical considerations it is evidently worth bearing in mind; but to what extent it has been influential in determining which species we should have or which we should not have, either in our two counties or in Britain as a whole, or to what extent it has, for instance, operated in the restriction to the area which they occupy, of the plants of what Mr. Watson calls the Germanic type of distribution, we can but guess vaguely.

About the basalt and porphyry we have said nothing as yet. The following is a type florula for one of our lower zone porphyritic crags, the cliff selected being one by the side of the Coquet, between Windyhaugh and Shillmoor, at an elevation above sea-level of from 630 to 700 feet.