Reports and Proceedings — Geological, Society of London. 47 



the average basicity of the rocks forming different bosses decreases 

 from north to south. 



The contact-metamorphisra is referred to ; and the presence of 

 hypersthene in the altered O^yg'm-shales, coupled with its absence 

 from the same shales where they have been affected by quartz- 

 syenite, leads the author to the conclusion that the chemical nature 

 of the intrusive rock does, in certain cases, produce an influence on 

 the character of the metaraorphism. 



Innumerable dykes and sheets of camptonite and bostonite are 

 associated with the above-mentioned plutonic bosses. These are 

 regarded by the author as having been produced by differentiation 

 from a magma having the composition of the average olivine- 

 gabbro-diabase. Analyses are given, and it is proved that a 

 mixture of nine parts of the average camptonite and two of the 

 average bostonite would produce a magma having the composition 

 of the average olivine-gabbro-diabase. The petrographical varia- 

 tions, such as the occurrence of pyroxenites and augite-diorites, in 

 the plutonic masses themselves are described, and attributed to 

 differentiation under physical conditions unlike those which gave 

 rise to the camptonites and bostonites. 



In discussing the general laws of differentiation the author points 

 out that it must have taken place before crystallization to any extent 

 had occui'red, because there is a marked difference in mineralogical 

 composition between the rocks occurring as bosses and those 

 occurring as dykes ; and, further, that it is dependent on the laws 

 which determine the sequence of crystal-building, in so far as the 

 compounds which, on given conditions, would first crystallize are 

 those which have diffused to the cooling margin, and so produced 

 a contact-stratum, of peculiar chemical composition, before any 

 crystallization had taken place. 



2. " On the Sequence of Perlitic and Spherulitic Structures (a 

 Eejoinder to Criticism)." By Frank Eutley, Esq., F.G.S. 



This paper relates to the order in which the perlitic and spheru- 

 litic structures have been develo^Ded in a felsitic lava of Ordovician 

 age from Long Sleddale, Westmoreland. The author having de- 

 scribed this rock in a paper, published in the Quarterly Journal of 

 the Society in 1884, and the accuracy of the views then expressed 

 having been questioned, now endeavours to confirm his original 

 statements, adclucing in support fresh observations made upon tins 

 and other rocks of a similar kind. 



3. " Enclosures of Quartz in Lava of Stromboli, etc., and the 

 Changes in Composition produced by them." By Prof. H. J. 

 Johnston-Lavis, M.D., F.G.S. 



The author describes the existence of enclosures of quartz in a 

 lava-stream at the Punta Petrazza on the east side of Stromboli, 

 and also in the rock of the neck of Strombolicchio. He describes 

 the effects of the rocks upon the enclosures, concluding that the 

 quartz has undergone fluxion but not fusion, and has supplied silica 

 to the containing lavas, thus causina; an increase in the amount of 

 pyroxene and a diminution in the amount of magnetite in the 



