634 MESSES. J. HOENE AND E. GKEENLY ON [Nov. 1 896, 



The minute penetration of gneiss, schists and sedimentary deposits 

 altered by contact-metamorphism, by granitic materials in the form 

 of excessively thin folia along the planes of schistosity was first 

 clearly described by Michel- Levy. In his paper ' Sur l'Origine des 

 Terrains Cristallins Primitit's ' he makes the following observations : 

 ' J'ai, le premier, appele l'attention sur le phenomene de penetration 

 in time, lit par lit, des roches granitiques et granulitiques eruptives 

 suivant les plans de schistosite des gneiss et des schistes . . . Mais en 

 outre, dans les zones de contact immediat sur la roche eruptive, le 

 quartz et les feldspaths s'insinuent, lit par lit, entre les feuillets des 

 schistes micaces ; on est parti d'un schiste argileux detritique, on le 

 trouve en definitive transforme en un gneiss recent, bien difficile 

 a distinguer des gneiss anciens.' l 



In 1890 Miss Gardiner described some of the contact-phenomena 

 produced by the granite near New Galloway, and showed how the 

 Silurian sediments pass into crystalline schists and gneiss with 

 various contact-minerals at the granite-junction. 2 



In the same year, while referring to the gneisses of central 

 Aberdeenshire, our colleague Mr. Hinxman states that the granitoid 

 character of the gneiss at certain points is due to the intrusion of 

 granitic material along the planes of foliation. 3 



In 1893 our colleague Mr. Barrow described in detail the meta- 

 morphism produced by an intrusion of muscovite-biotite-gneiss in 

 the South-eastern Highlands. He showed that the normal con- 

 dition of the intrusive rock is that of a slightly foliated granite with 

 two micas, but with considerable variation as regards structure and 

 composition, the larger masses being more or less fringed with 

 pegmatite. The foliation of the larger masses is rudely parallel to 

 that of the surrounding schists, and though their intrusive nature 

 is therefore not so obvious, it has been proved by detailed mapping 

 that these masses traverse different bands of the schists. The 

 crystalline gneisses and schists with the contact-minerals, sillimanite, 

 cyanite, and staurolite, arranged in zones according to the stages of 

 metnmorphism, are held to be due to the intrusion of muscovite- 

 biotite-gneiss. 4 



In 1890 the Geological Survey first broke ground in the east of 

 Sutherland from Melvich as a centre : the coast-line between Strath 

 Halladale and Armadale having been assigned to Mr. Greenly. On 

 the shore at Portskerry he observed minute granitoid folia radiating 

 from the larger granite masses and traversing the granite-like 

 schists. Mr. B. N. Peach mapped the larger sills of acid igneous rock 

 in Strath Halladale and clearly recognized their intrusive character, 

 ascribing the foliation of the granite to dynamic action. In the 



1 Bull. Soc. Geol. France, ser. 3, vol. xvi. (1888) pp. 104, 107. 



2 ' Contact- Alteration near New Galloway,' Quart. Journ. Geol. Soc. 

 vol. xlvi. p. 569. 



3 Geol. Surv. Scotl. Explanation of Sheet 76, p. 12. 



4 ' On an Intrusion of Muscovite-biotite-gneiss in the South-eastern 

 Highlands of Scotland and its Accompanying Metamorphism,' Quart. Journ. 

 Geol. Soc. vol. xlix. p. 330, 



