SECTIONAL TRANSACTIONS.— C. 421 



Mr. S. O. Agrell. — Adinoles of Dinas Head, Cornwall (2.45). 



Adinoles associated with spilosites and spotted slates occur at the contact 

 of an albite-dolerite intrusion with black limestone-bearing slates of Upper 

 Devonian age. 



They consist of albite and quartz with accessory leucoxene, and with or 

 without chlorite, dravite, ankerite and calcite. 



Four main types are recognised : 



1. Normal adinoles — structureless albite-quartz rocks showing sedi- 

 mentary banding and grading into rocks composed essentially of 

 dravite. 



2. Adinoles with pseudomorphs probably after andalusite. 



3. Adinoles with globular masses of ankerite showing concentric 

 structures. 



4. Polygonal and spherulitic adinoles. 



Chemically, the adinoles resemble quartz-keratophyres and their tuffs, 

 but the evidence at Dinas Head shows that they are due to the effect of the 

 intrusion on the sedimentary rocks. The first change was purely thermal 

 and was followed by albitisation and then by carbonatisation, the meta- 

 somatising fluids coming from the dolerite. 



The adinolisation is a volume for volume replacement and calculation on 

 analyses shows that soda, silica and sometimes boric oxide have been fixed 

 in the slates. 



As a result of faulting and of the ramifications of the intrusion the adinoles 

 appear up to eighty feet thick, but actually, they form a veneer over the 

 headland and never extend more than thirty feet from an igneous contact. 



Mr. G, Andrew. — Some granitic intrusions in the Central Eastern Desert 

 of Egypt {3.15). 



The intrusive granites may be divided into groups on the basis of the 

 nature of the contact. 



1 . Abu Ziran type. — Injection-gneiss, strongly banded, generally foliated, 

 protoclastic or cataclastic structures common. Xenoliths within mass 

 granoblastic, near margin foliated. Injection zone in pelitic rocks accom- 

 panied by kyanite, staurolite and almandine as contact minerals. Re- 

 crystallisation falls off away from granite-margin, but is still of regional 

 type. Intrusion of syntectonic type. 



2. Belih type. — Porphyritic, often foliated locally. Contact irregular, 

 either steeply plunging discordant, or approximately horizontal discordant 

 in bathyliths. Country-rock thoroughly recrystallised, normal homfels- 

 structures and contact-minerals, veined. Assimilation considerable, with 

 xenoliths common and remote from margin, traceable in granite in the form 

 of ' basic clots.' Margin usually granite-porphyry. 



3. Um Disi type. — Even grained, often fine-grained, non-porphyritic, 

 unfoliated. Contact sharp, steeply plunging discordant. Country-rock 

 affected to a notably less degree in comparison with Belih type. Normal 

 hornfels-structure and minerals. Veining rare, assimilation negligible, and 

 xenoliths are rare, and sharply bounded. Margin often coarse, pegmatitic. 



4. El Atrash type. — Almost entirely a quartz-feldspar rock, in small 

 miasses, frequently with a dyke form (W.N.W. to N.W. strike). Coarse 

 varieties granitic, finer grained type is spherulitic or micrographic. Contact 

 metamorphism very slight, confined to a few metres width, even in masses 

 of 4 sq. km. area. Rarely xenolithic. 



Type I is only known in the regionally metamorphosed paraschists south 

 of G. Me'atiq. The remainder intrude the Dokhan series and other 



