Page:Transactions of the Natural History Society of Northumberland, Durham, and Newcastle-upon-Tyne (1867).djvu/17



As the principal object of this memoir, on the geology of Northumberland and Durham, is to supply data to help the botanist to see how far the Flora of these counties is influenced by their geological structure, I shall especially direct attention to the mineral character and range of the various rock formations. Nevertheless, the consideration of more general questions will not be altogether avoided; the classification of groups of strata, according to age, will be attempted; their organic history will be indicated; and as relative elevation itself gives a character to vegetation, it will be necessary to notice in passing, the disturbing agencies which at different periods have rent the strata and lifted up our mountains, or left an impress on the general contour of the surface.