112 J. H. Teall — Cheviot Quartz-Fehites and An gife- Granites. 



In addition to the quartz-felsites above described, there are others 

 in the granitic region ; but as these, at any rate in places, appear to 

 me to be of the nature of contemporaneous veins, I will refer to such 

 as I have observed in describing the granitic rocks. 



The Augite-Biotite-Granitb. 



It has long been known that in the sparsely populated but by no 

 means inhospitable recesses of the Cheviot Hills extensive tracts of 

 granitic rocks occur. The precise relations of these rocks to the 

 porphyrites have not yet been described, and we must wait until the 

 Survey Maps and publications are out before we can obtain detailed 

 information on this subject. My own knowledge of these rocks, as 

 they occur in the field, was obtained during two short excursions ; 

 one to Linhope Spout, the other involving a ■walk from Usway Ford 

 round the head-waters of the Breamish, by Staindrop Kigg and 

 Hedgehope, to Langley Ford in the valley of the Harthope Burn. 

 As it was necessary to get from Usway Ford to Wooler in one day, 

 there was no time available for a search for junctions, and 1 had to 

 content myself with collecting specimens of such rocks as came in 

 my way. 



The principal interest attaching to these rocks centres in the fact 

 that they present us with a type hitherto unknown in Britain, and 

 by no means widely recognized in other parts of the world. 

 They are true augite-bearing granites similar in all essential re- 

 spects to the augite-granite of Laveline in the Vosges, described by 

 Eosenbusch,^ and that of Oberbruck also in the Vosges, described 

 hy Cohen.^ Prof. Eosenbusch has seen my specimens, and agrees 

 with me in my determination ; he has also very kindly supplied me 

 with specimens of the rocks from Laveline and Oberbruck. 



As the augite is the most interesting constituent, I will describe 

 it before proceeding to refer to the rocks in which it occurs. It is 

 present in the form of irregular grains, granular aggregates, and 

 sometimes, though rarely, in more or less definite crystals. It is 

 almost colourless in thin section, exhibiting only a slight inclination 

 to a pale green tint. Inclusions of magnetite are not uncommon. 

 Cross sections show the characteristic cleavages of augite, and 

 longitudinal sections give a maximum extinction of 43° or 44°. 

 Twinning may occasionally be observed. Alteration tends to 

 develope serpentinous and not chloritic products, and the separation 

 of iron-oxide appears to accompany the change. In appearance the 

 mineral is identical with the augite of the Vosges rocks above 

 referred to, and we may safely conclude that it has an analogous 

 composition. 



Dr. Alphonse Merian ^ has recently isolated and analyzed the 

 augite of the Laveline rock, and he finds that it possesses the 

 following composition : — 



1 Z. D. G. G. 1876, p. 369. ^ Neues Jahr. 1883, vol. i. p. 200. 



^ Stiidien aa gesteiiisbiidenden Pyroxenen. Neues Jahrbuch III. Beilage Band, 

 p. 262. 



