2 A NilW FLORA OF 



The two counties liave an area of 2905 square miles. The 

 surface of the district rises from the sea coast to the westward, 

 as far as the elevated ranges, forming the backbone of England, 

 and the dividing ridge between the eastern and western coasts ; 

 and hence all the rivers and streams flow eastward into the 

 German ocean. The western boundary, on the northern part 

 of liorthumberland, is formed by the porphyritic range of the 

 Cheviots, the highest elevation being 2676 feet; and further 

 southward by sandstone hills and ridges from 500 feet to 1809 

 feet in height. Southward of the Tyne, the whole slopes away 

 from the Penine range, whose culminating point. Cross Fell, 

 2901 feet above the sea level, is but a short distance beyond the 

 district. The physical aspect is therefore very varied : along 

 the coast are some broad plains ; further inland are low rolling 

 hills, and then long broad high ridges, expanding into dreary 

 moorlands ; but on the western borders there are, in some parts, 

 fine conical smooth hills, and in others high rugged cliffs. A 

 few wide valleys there are through which larger rivers flow ; 

 but the burns and waters wend their way from the hills through 

 contracted vales and narrow picturesque denes. This inequality 

 of surface is of itself favourable to the production of a varied 

 Flora; and these conditions have been made more favourable 

 still by the variety of the rock formations ; for not only are there 

 series of strata, differing in mineral character and disintegrating 

 capability, from the old Greywacke up to the ISTew Eed Sand- 

 stone, but also a number of igneous rocks in mountain ranges, 

 in overlying masses, and in lateral and vertical dikes. 



In describing the geology of this district I shall begin with 

 the oldest sedimentary strata, and follow the succession of for- 

 mations up to recent deposits, and then notice the various igneous 

 rocks. The whole are arranged in the following table : — 



AQUEOUS EOCKS. 



PALAEOZOIC ERA. 



I. Cambeo-Silxjetan System. 

 II. Upper Old Red Sandstone Fokmation. 



