Reports C& Proceedings — The Royal Society. 283 



into three series, the Amisk series of volcanic rocks at the base, 

 followed by the Kisseynew gneisses ; above these are the Lower and 

 Upper Missi series, probably separated by an unconformity, and these 

 are cut by gneissose granite. The main interest is economic, the 

 minerals including gold-quartz veins and chalcopyrite-sphalerite 

 replacements, both believed to be genetically related to the granite 

 batholiths. 



On the Origin of the Kuroko op the Kosaka Copper Mine, 



ISioRTHERN Japan. By R. Ohashi. Journal of the Akita 



Mining College, 1920. pp. 11-18, with 2 figures and 2 plates. 



Akita, 1920. 



TT'UROKO is a dense black ore consisting of sphalerite, galena, 



-*-^ and barytes, usually with accessory pyrite, chalcopyrite, and 



quartz. Its formation has been attributed by most writers to 



metasomatism, but this explanation presents certain difficulties, 



especially from the absence of any sign of chemically active 



substances. The author, therefore, supports the theory of Fukuchi 



and Tsujimoto, that these deposits are masses of sinter deposited on 



the floor of the sea by hot springs, contemporaneously with the 



formation of the clay-beds in which they are now found ; the springs 



were connected with the erujDtion of the mterbedded rhyolites. 



REPORTS AND PROCEEDINGS. 



The Royal Society. 

 April 29, 1920.— Sir J. J. Thomson, O.M., President, in the chair. 



" The Irish Eskers." By Professor J. W. Gregory, F.R.S. 



Eskers are banks of sand and gravel, typically occurring as ridges 

 on the central plain of Ireland, where they were deposited during 

 the recession of the ice at the close of the Glacial period. They have 

 been generally attributed to dej)osition along glacial rivers, like 

 Swedish osar. Their structure and composition indicate that the 

 most important Irish eskers were formed along the margin of the 

 receding ice-sheets by floods of water, due to the melting of the ice. 



Irish eskers formed along glacial rivers are relatively small and 

 exceptional . The accumulation of the materials into ridges, and their 

 restriction between about 150 and 300 feet above sea-level, are 

 attributed to the formation of the eskers where the ice entered into 

 a sheet of water, which was probably the sea, since marine fossils 

 are widely distributed in the adjacent drifts, and there are no 

 embankments to maintain glacial lakes at the required level. 



It is proposed that the term esker should be continued for Irish 

 ridges and mounds of sand and gravel, but that in glacial geology 

 the term osar should be used for ridges formed along the glacial 

 rivers, and kame used for ridges deposited along the margin of an 

 ice sheet. 



