Mr. George Tate on the Cheviots. 361 



the scene. Great pillared rocks appeared, and long trains of 

 purple ston£S blending their tints with the bright green herb- 

 age ; crags crested the summits, or broke out of the sides of 

 some of the hills, resembling ruined towers and castles, and 

 the hills and valleys rolling into each other appeared to rise 

 and fall like the billows of a great ocean. 



Mineral Character. 



Igneous rocks are conveniently arranged in two divisions ; 

 the felspathic or plutonic, and the augitic or volcanic. Gran- 

 ites and porphyries belong to the former, and basalts and trap 

 rocks to the latter. Generally, too, the former are much 

 older than the latter ; and, notably, this is the case in the 

 Border counties, where the basaltic whin sill and basaltic 

 dikes belong to a much more recent era than the Cheviot 

 porphyry and syenite. 



The great mass of the Cheviots is formed of felspathic or 

 plutonic rock, of which we may distinguish two groups — one 

 porphyritic and the other syenitic ; which, though essentially 

 of the same composition, yet are structurally different, as the 

 former has a compact base, while the latter is entirely 

 crystalline. 



I. Of Porphyry there are several varieties. 



1. JRed porphyrite, the most abundant of all, is composed 

 of a base of felsite, through which are scattered crystals of 

 orthoclase or common potash felspar; and this is often 

 specked with minute crystals of hornblende. The colour 

 readily distinguishes this variety; but as it is distributed 

 throughout the whole range, localities need not be given. 



2. DoleritOf which is usually of a dark grey colour and 

 composed of labradorite or soda felspar and augite, is widely 

 distributed, but not so abundantly as porphyrite ; it occurs at 

 Housey Crag, Langley Hope, Dunsdale, Yevering, Tom 

 Tallon's Crag, Yetholm, Reaveley, Prendwick, Alwinton, 

 &c. In some places, as at Coldbnrnlaw and Hawsen burn, 

 it is magnetic. At Prendwick, Yevering, and a few other 

 localities, it is traversed by veins of porphyrite specked with 

 crystals of hornblende. Though having more of the character 

 of the felspathic division of igneous rocks, the dolerite of 

 the Cheviots has some alliance with the augitic division, not 

 only in mineral composition, but, also, in some cases, in its 

 structural form ; in the Hawsen burn it appears in rude 

 quadrangular columns, made up of short tabular prisms only 

 a few inches long ; and these, too, are slightly magnetic. 



