422 SECTIONAL TRANSACTIONS.— C. 



unmetamorphosed sediments, and are arranged in order of age. The 

 riebeckite granites are not included in this table and form a still younger 

 group than 4. 



Mr. G. Andrew. — On the upper pre-Cambrian of the Eastern Desert of 

 Egypt (3 -so)- 



Between latitude 26° N. and 28° N. the stratified rocks forming the hill 

 region west of the Red Sea are largely unmetamorphosed. Three series 

 may be distinguished : 



3. The Hammamat series, consisting of purple (lie-de-vin) and green 

 mudstones, greywackes and conglomerates. 



2. The Dokhan series, consisting of similar sediments, with intercalated 

 pyroclastic rocks and lavas. 



I. The Atalla Rubshi series : grey mudstones, often phyllitic, some 

 greywackes, and rhyolites with tuffs. 



The stratigraphical relations of the three series to one another are not 

 known, since all contacts seen are faults. Dips are high, strikes variable : 

 north-north-west in the Atalla-Rubshi series, north-west to north-north- 

 west in the Hammamat, and north-east to north in the Dokhan series. 

 The lithological types of the Hammamat series may be recognised over a 

 wide area in an unmetamorphosed state, e.g. Bir Kareim, Dungash, Wadi 

 Khashab, Wadi Hamata, and north of Um Garaiart. In the same way the 

 Dokhan type occurs in Wadi Hamish (Wadi Shait), Wadi Sheikh Shadli — 

 G. Abu Hammamid, Wadi Huluz, and in the Wadi Allagi region. The 

 Atalla-Rubshi series is less distinctive, and not recognisable elsewhere at 

 present. These series may be classed as Algonkian, and include the 

 Eparchaean and part of the Metarchaean of Hume (1934). The rocks are 

 typically non-schistose, except in narrow zones of movement, and in the 

 contact-zone of some granites. 



Dr. A. G. MacGregor. — Characteristics of West Indian tridymite and 



cristobalite (3.45). 



Exhibit of microphotographs (lantern slides) illustrating the mode of 

 occurrence and diagnostic features of the tridymite and cristobalite of the 

 porphyritic bandaites (labradorite-phyric dacites) of Montserrat, B.W.I. 

 Tridymite is an abundant primary groundmass-constituent ; cristobalite is 

 also very prevalent and can, in some cases, be shown to replace original 

 tridymite. The cristobalite exhibits certain features recalling those often 

 described as characteristic of tridymite. 



Wednesday, August 24. 



Dr. E. B. Bailey, F.R.S. — Caledonian tectonics and metamorphism in 

 Skye (lo.o). 



The geology of the Kishorn Nappe is reviewed from Loch Kishorn on 

 the mainland through the greater part of Sleat in Skye. The fundamental 

 facts are taken from Peach, Home and Clough. The latter 's magnificent 

 work in Skye has been amended in certain details, and this has tended to 

 clarify the general situation. 



The Kishorn Nappe consists mainly of Torridonian, with Lewisian 

 north of Loch Alsh (Sheets 81, 71), and Cambro-Ordovician west of Ord 

 on Lobh Eishort (Sheet 71). The nappe is underlain through much of its 



