Reports cC; Proceedings — Liverpool Geological Society. 187 



Liverpool Geological Society. 



13^^ December, 1921.— Professor P. G. H. Boswell, O.B.E., D.Sc, 

 F.G.S., President, in the chair. 



The following communications were read : — 



1. " Note on the Natural Panning of Minerals in Littoral 

 Deposits," by Nigel W. Kennedy. 



The separation of the various mineral constituents of littoral 

 sands by a purely natural aqueous agency has not hitherto been 

 definitely recorded, and the author has therefore described his own 

 observations during the past few months on the sands of the Mersey 

 shore, where the process may be seen in operation. 



Black sand, containing a great variety of rare heavy minerals, 

 occurs in irregular patches of several square yards in area on the 

 flat parts of the shore near the tidal limits, and also on the sides of 

 ripple marks facing the sea. In the latter case the separation is 

 held to be due to wave action alone, but in the former the sun's 

 heat and jjrevalent strong sea breezes have also played a part, and 

 the details of the process as observed were fully described. The results 

 of observations on the mechanical separation of the constituents of 

 dry sand on the slopes of dunes are also given. 



2. " The Igneous Kocks of the Capel Curig District," by Howel 

 Williams, B.A. 



The district studied covers an area of some 10 to 12 square miles 

 in the south-east corner of Snowdonia, with the village of Capel 

 Curig as its centre. The dominant rocks are all igneous, either 

 lavas, ashes, or dolerites, and the associated sediments are also 

 largely the result of the breakdown of the volcanic rocks, so that the 

 geology of the area is necessarily and primarily a study of vulcanicity. 

 A general account of the vulcanicity of Snowdonia as a whole was 

 first given, including a discussion of the related crustal movements, 

 and a detailed description of the rock types in the localized area 

 followed, together with a consideration of their position in the 

 Ordovician series. The Capel Curig rhyolites according to the 

 a,uthor's researches differ from those of the Snowdonian group 

 proper in that they (1) are more porj)hyritic, (2) show banded and 

 nodular structures, (3) are seldom associated with thick tufis, 

 (4) are garnetiferous and pyritiferous, (5) are freer from impurities 

 (absorbed muds, etc.), (6) are generally less devitrified, (7) are richer 

 in iron ores and viridite (also prochlorite and cordierite), while the 

 Snowdon lavas (1) contain mispickel, (2) are usually highly mixed 

 with tufis, and (3) have not the thickness of the Capel Curig flows. 

 Evidences of solfataric action are seen in the occurrence of garnets 

 and in the associated tourmaline grits. 



The tuffs can be classified as (1) purely vitric, (2) detrital vitric, 

 (3) crystal and lithic, (4) agglomeratic tuff or breccia. The dolerites 

 •occur usually as sills and dykes, and with few exceptions are augite- 

 dolerites of spilitic character. They include a peculiar differentiation- 



