G. W. Tyrrell — Intrusions of Kihyth-Croy Didrict. 359 



Septifer cf. LiNEATUs, J. dc C. Sowerby, sp. 

 Horizon. — Cretaceous (shales) [Hume]. 



Locality. — Abu Rahal, 40 kilometres east of Edfu (well boring 50 metres = 

 164 feet depth). 



BRACHIOPODA. 



LiNGULA sp. 



Horizon. — Cretaceous (shales) [Hume]. 



Locality. —khM Rahal, 40 kilometres east of Edfu (well boring 50 metres depth). 



PLANTS. 



Araucarioxylon (Dadoxylon) ^gyptiacum (Krauss), Unger. 

 Horizon. — Senonian (Campanian) [Blanckeuhorn]. 



Localiti/. — Aswan and Um-Ombos ( = Kora Ombo), between Aswan and Edfu; 

 Dakhla Oasis (recorded by Schenk in Zittel). 



NicoLiA ^GYPTiACA, Uuger. 

 Horizon. — Senoniau (Campanian) [Blanckenhoru]. 

 Locality. — Libyan Desert (east of Regenfeld ; see Zittel). 



Weichselia sp. ( = Fern). 

 Horizon. — Wealden [Seward]. 



Locality. — North-west of Um Garaiart, Wadi Alagi, Northern Nubia (about 

 70 kilometres eastward of the Nile). 



Clathropteris Egyptiaca, Seward ( = Fern). 

 Horizon. — Lower Jurassic [Seward] ; Upper Cretaceous [Hume]. 

 Locality. — Between "Wadi Dum and "Wadi Abbad, east of Edfu. 



[To be concluded in our next Number.) 



VI. — Geology and Petrology of the Intrusions of the Kilsyth- 



Croy District, Dumbartonshire. 



By G. "W. Tyrrell, A.R.C.Sc, Assistant in Geology, Glasgow University. 



[Concluded from the July Number, p. 309.) 



V. Mutual Relations and Order of Crystallization of the 

 Essential Constituents. 



rpHE general appearance of this rock in thin section is of an 

 X interlocking framework of plagioclase, augite, and iron-ores, with 

 micropegmatite occupying the interstices. The mutual relations of 

 the felspar and augite Tar\' considerably. The felspar may be entirely 

 enclosed in the augite. In this case it is very basic and only faintly 

 zoned. The most common relation is for the augite to enclose the 

 terminations of the felspar laths, the sub-ophitic structure of Watts. ^ 

 But frequently idiomorphic crystals of augite are found partly or 

 wholly enclosed in felspar. The latter is then more acid than the 

 ophitic felspar, and is broadly zoned. These varying relations may 

 frequently be found within the limits of a single slide. 



These facts may be completely explained on the hypothesis that 

 felspar substance separated from the magma during practically the whole 

 process of crystallization ; whilst the separation of the pyroxenes was 

 episodal, beginning after the first separation of felspar, thus enclosing 

 some of the earlier basic crystals, and ending before the complete 

 separation of the later, more acid felspars. The latter were therefore 



' Ancient Volcanoes of Great Britain, vol. i, p. 417. 



