Vol. 56.] KENTALLENITE AND OTHER ARGYLLSHIRE ROCKS. 531 



28. On Kentallenite and its Relations to other Igneous Rocks in 

 Argyllshire. By J. B. Hill, Esq., R.N., and H. Kynaston, 

 Esq., B.A., F.G.S. (Read May 23rd, 1900.) 



[Communicated by permission of the Director-General of 

 H.M. Geological Survey.] 



[Plates XXIX-XXXI.] 



Contents. 



Page 



I. Introductory 531 



II. Distribution, Mode of Occurrence, and Description of 



the Rocks 532 



III. The Eelation between the Kentallenites and the Granites 



and Diorites 541 



IV. The Relation between the Kentallenites and the Lampro- 



phyres 548 



V. General Considerations 551 



VI. Summary 555 



(Map on p. 542.) 



I. Introductory. 



In Mr. Teall's well-known work on ' British Petrography ' a remark- 

 able rock from the Kentallen quarries, near Ballachulish in Argyll- 

 shire, was figured and briefly described, 1 but it was not until the 

 rock had been mapped by Mr. J. Grant- Wilson in 1896 that its 

 peculiar characters were recognized and more fully described by 

 Mr. Teall in the Annual Report of the Geological Survey under the 

 term olivine-monzonite. 2 This term was assigned to the rock 

 on account of the resemblance which it showed to the monzonite- 

 group of Prof. Brogger. 3 Mr. Teall pointed out, however, that 

 there was at the same time a considerable difference, consisting 

 mainly in the relative proportion of magnesia, between the Highland 

 rock and the olivine-monzonite rock of Brogger. Since that time 

 similar and closely-allied rocks from other localities have been in- 

 vestigated by us; and it is our object in the present paper to en- 

 deavour to point out the relationships of this unique petrological 

 type to the granites and other intrusive rocks of Argyllshire, and 

 so to remove it from a hitherto somewhat isolated position. More- 

 over, an examination of several varieties of the normal type has led 

 us to reconsider the advisability of retaining Prof. Brogger's term for 

 a group of rocks which evidently show in certain respects a marked 

 divergence from the original type. 



The term monzonite originates from Prof. A. de Lapparent 

 (1864), who applied it to the well-known augite-syenite of Monzoni, 



1 J. J. H. Teall, 'Brit. Petrogr.' 1888, pi. xvi, fig. 1. 



2 Ann. Rep. Geol. Surv. 1896 [1897] pp. 22 & 23. 



3 'Die Eruptionsfolge der triadischen Eruptivgesteine bei Predazzo in 

 Siidtyrol ' no. ii of ' Die Eruptivgesteine des Kristianiagebietes ' Vidensk. Skrift. 

 No. 7, Kristiania, 1895. 



