J. H. Teal! — Cheviot Quartz-Fehites and Augite- Granites. 115 



very little biotite may be observed in tlie mass of the rock at 

 Staindrop Eigg. 



Comh Fell. — I collected several specimens from the western side 

 of Comb Fell. They are all varieties of a pinkish biotite granite, 

 in which orthoclase appears to be the dominant felspar. Augite is 

 present only in very small quantity. 



Jledgehope. — This mountain is largely if not entirely composed of 

 granite. Specimens from the eastern side are similar in character 

 to those from Staindrop and therefore require no special description. 



In taking a general view of the holocrystalline granitic rocks of 

 the Cheviot District one fact stands out in a prominent manner. 

 They are hj no means uniform in composition. Some are rich in 

 basic minerals, others are comparatively poor ; some contain plagio- 

 clase, others a soda-orthoclase, as the dominating felspar. The dif- 

 ferent varieties do not appear to be in all cases sharply separated 

 from each other. A possible explanation of this variability will be 

 referred to later on. 



Comparison of the Cheviot Augite-gkanites with allied 



KOOKS op other DISTRICTS. 



The occurrence of augite rocks containing quartz and orthoclase is 

 such a striking violation of one of Breithaupt's laws of paragenesis 

 as to give these Cheviot granites a special interest. 



This occurrence was first recognized according to Rosenbusch ^ 

 by Vom Kath in the case of a quartz-porphyry from Campiglia 

 (Tuscany), which contains orthoclase, plagioclase, augite, magnetite, 

 mica, and quartz. In North Saxony, near Leipzig, there is an exten- 

 sive development of augite-bearing quartz-porphyries. These rocks 

 have been investigated by Tschermak, Naumann, Kalkowsky, Rosen- 

 busch, and Penck. They are classed with the upper portion of the 

 middle Rothliegende by the last-mentioned author.^ Rosenbusch ^ 

 has identified a rhombic as well as a monoolinic pyroxene in these 

 rocks, and I may mention that in one case I observed in a Cheviot 

 granite a mineral that was most probably enstatite or bronzite. 



Then again there are the remarkable pyroxene-granulites of the 

 granulitic region of Tuscany which have been described by Stelzner,* 

 Dathe,^ and Lehmann.^ These have been divided by Dathe into 

 orthoclase- and plagioclase-diallage-granulites, according to the 

 nature of the dominant felspar. They contain monoclinic and 

 rhombic pyroxenes, and in this respect resemble the quartz-porphyries 

 of North Saxony. Until recently they have always been regarded 

 as Archaean, but the work of Dr. Lehmann has destroyed much of 

 the evidence on which this conclusion was based. 



In the same connexion we must mention the quartz-less augite- 

 syenites of Monzoni, described by Vom Rath,' and those of Norway 



1 Massige Gesteine, p. 68. 



- Die pyroxen-liihrendeii Gesteine des nord-sachsichen Porphyrgebietes, Min. 

 Mitth. 1881, p. 72. 3 Massige Gesteine, p. 58. 



4 Neues Jahr. 1871, p. 246. s z. D. G. G. 1877, p. 285. 



^ Die Entstehung der alt-krystallinischen Scliiefer-gesteine, p. 228. 

 1 Z. D. G. G. 1876, 343-357. 



