NOETHUMBEELAND AISTD DTJBHAM. 35 



and rent by volcanic forces, most probably when beneath the sea ; 

 and, at remitting intervals, molten lava was poured out of fissures 

 generally in a line from north north-east to south south-west, 

 partly over the sea-bed, and partly thrust in among the stratified 

 rocks which it metamorphosed; and, cooling slowly, under the 

 influence of considerable pressure, this lava assumed the stony 

 crystalline character of basalt. Mr. Hopkins has shown how 

 minor fissures are formed transverse to the chief line of fracture, 

 and therefore it is highly probable that the transverse basaltic 

 dikes are due to the same causes which produced the Whin Sill. 

 Some plants in JS'orthumberland are confined to the igneous 

 rocks, and chiefly to the augitic group. Bianthus deltoides is 

 common to the porphyry and basalt : I have seen it on the very 

 verge of the porphyry, but I could not, after diligent search, find 

 a single specimen straying across the border to a stratified rock. 

 Pyrola secutida, and Teesdalia nudicaulis, have not been noticed 

 except on porphyry. But the following occur in Northumber- 

 land only on the basalt : Ilc&nchia erecta, Sagina subulata, Vicia 

 lathyroides, Asperugo procumiens, Statice limonium, Convallaria 

 polygonatum, Allium schoenoprasum, Scilla verna, Sedum anglu 

 cum, Asplenium septentrionale, Asplenium germanicum. Selian^ 

 themum vulgare, although also occurring in limestone, I have 

 sometimes found a useful guide in tracing the range of the "Whin. 

 SiU. 



POSTSCRIPT TO CHAPTER I. 



ADDITIONAL OBSERVATIONS ON THE INFLUENCE OF THE SUBJACENT 

 ROCKS ON PLANT DISTRIBUTION, BY J. G. BAKER. 



From the more strictly botanical point of view I propose to sup- 

 plement Mr. Tate's sketch by a few observations on the influence 

 exercised by the character of the subjacent rocks on the distribu- 

 tion of the Flora. The sedimentary beds of the north-east of 

 England fall under two well-contrasted types in their influence 

 on the scenery and botany. These,*' following the nomenclature 



* Thurmann. Essai de phytostatiqiie applique a la chaine du Jura. Berne, 1849, 



