56 TKOF. T. G. BOXXEY AXD THE EEV. E. HILL: [Feb. I9I2, 



(including mica-traps). Is it possible that the diorites, granites, 

 and aplitic dykes of the Channel Islands may be the consequences 

 of a much more ancient, even pre-Cambrian, set of movements, of 

 which our Charnian axis, with its associated intrusives, is a relic ? 



EXPLANATION OF PLATE I. 



[All the figures are drawn with ordinary light, and magnified 20 diameters.] 



Fig. 1. Diorite, from Bouet Quarry (Griierusey). Two grains of unchanged 

 augitelie on a line drawn south- south-westwards from the numeral 1. 

 Rising from the upper one and in the left-hand segment are horn- 

 blendes (darker in tint). (See p. 35.) 



2. 'Birdseye' diorite, from Hougue a la Perre. Several grains ofaugite 



(tinted as in the last specimen), some of which are partly altered into 

 hornblende (darker in tijit). (See p. 35.) 



3. Streaky red dyke, under Castle Cornet. The small dark-tinted prisms 



are the biotites or hornblendes of the green streaks. The white is 

 quartz ; the pale tints represent felspar. (See p. 41.) 



4. Black rock, enclosed in red dyke, east of the breakwater, St. Peter 



Port. The lighter-tinted grains are the pale hornblende, the darker 

 part felspar, rather decomposed. (See p. 43.) 



5. Quartz-felsite dyke, Castle Cornet. The colourless grain on the right 



is quartz, the darker on the left decomposed felspar. Traces of a 

 spherulitic structure can be seen. (See p. 43.) 



6. Pleinmont rock [specimen 5, E. Hill]. The colourless grains are the 



larger fragments of quartz. (See p. 49.) 



[Fig. 3 on p. 42 is a reproduction of a drawing, made from a specimen in 

 Prof. Bonney's collection by Miss Ethel Wetherall.] 



Discussion. 



Dr. J. W. Evans remarked on the large number of different 

 igneous rock-types described by the Authors as succeeding each 

 other through a long period of the earth's history. He suggested 

 that they might be divided into groups, the members of each 

 of which belonged to a separate cycle of intrusions. The diorites 

 were, for instance, followed by the hornblende-granites, showing 

 the usual succession from basic to acid in plutonic rocks ; ^hile 

 the microgranite and diabase-dykes showed the contrary order, 

 which is normal in minor intrusions. He asked the Authors 

 whether there was any evidence of the character of the dis- 

 tribution of the products of the segregation of the diorites. Did 

 the basic material gather to the margins, as was usually the case 

 in comparatively small igneous reservoirs ; or did it form the lower 

 portion of the mass, as appeared to happen in those of greater 

 dimensions ? 



ATr. T. 0. BoswoETH enquired whether the contact between the 

 granite and the diorite was as simple as suggested b}- the line 

 on the map, or whether there occurred any of that intricate 

 penetration so frequent where diorite and granite are associated. 



The Eev. E. Hill said, in regard to the remark on the number 

 of varieties of intrusive rocks, that on the tiny area of Castle 



