466 Reviews — Geological Survey of Great Britain. 



Part II. Pwll Strodyr to Pencaer (0. T. Jones). 

 The following rock-groups are represented in probable descending 

 order : — 



Lower or 

 Arenig 



? Lower Arenig 



LiNGULA Flags 

 Doubtful Age 



Middle Pwll Deri Slates 



Aberbach Quartzite Group 

 probably equivalent to 

 the quartzites of Trwyn 

 Llwyd and possibly of 

 Pwll Strodyr. 



Mynydd Morfa Group. 



Pwll Crochan Group . 



? Solva Llech Dafad Group 



Cleaved dark slates with 

 extensiforni graptolites. 



Quartzites with thin dark 

 shales. 



Dark slates with obscure 

 fossils probably Mene- 

 vian or Upper Lingula 

 Flags. 



Quartzites, green and purple 

 sandstones ; obscure 

 fossils. 



The age and relationships of the various groups are briefly discussed, 

 and reference is made to certain intrusive rocks which occur among 

 the lower groups. 



In view of the great thickness of some of the groups and of the 

 bearing of their age upon the igneous rocks of Pencaer and Strumble 

 Head it is proposed to map the area in detail. 



I^E"VIE"VvrS. 



I. — Summary of Progress of the Geological Survey of Great 

 Britain and the Museum of Practical Geology for 1912. 

 8vo ; pp. iv, 101, with 1 plate and 4 text-illustrations. London: 

 printed for H.M. Stationery Office, 1913. Price Is. 



IN this memoir, as usual, there will be found much to interest all 

 geologists, whether their special studies are among the Archaean 

 schists or on succeeding geological systems up to the time when 

 Palaeolithic Man occupied the country. In England and Wales 

 field-work has been carried on in three districts : Denbighshire, 

 Warwickshire and Staffordshire, and London with the south-eastern 

 counties. In Scotland the districts comprise the West Highlands, 

 North and Central Highlands, Kilmarnock in Ayrshire, and South 

 Lanarkshire. 



Attention is called to the occurrence in Ben Armine Forest, 

 Sutherland, of an altered peridotite, which is in contact with gneisses 

 of Lewisian type and granite intrusions, and was probably intruded 

 prior to the movements which caused the schistosity of the rocks. 

 The subsequent remarkable effects of granitization are described. 



The mapping of some of the older Palaeozoic rocks on the western 

 borders of the Denbighshire Coal-field has been revised, and it has been 

 found that the Tarannon Shale does not rest unconformably upon the 

 Ordovician, but that the Llandovery Beds are present, and no evidence 



