296 H. A. Baker — The Pre-Thanetian Erosion 



copper minerals, as well as in pegmatites with quartz, oligoclase, 

 and muscovite.^ The general association of the scheelite deposits of 

 California is with siliceons gold veins in connexion with, granites. 

 This shows a distinct resemblance to the wolfram-gold association of 

 Boulder County, Colorado, but in California more lime is present in 

 the rocks, and therefore scheelite has been formed instead of 

 wolfram. 



In the Federated Malay States scheelite occurs in considerable 

 quantity in addition to wolframite. A particularly interesting case 

 liiis been noticed at Salak.' It is a lode about 12 feet wide, con- 

 sisting of scheelite, quartz, and light-yellow tourmaline, with traces 

 of arsenic and copper. Another scheelite vein also contained fluorite 

 and axinite with a little quartz. There are several other instances 

 of scheelite lodes all apparently more or less closely associated with 

 granite-limestone contacts. The mineral is also found to a small 

 extent in the gold veins of the Raub mines, where the country rock 

 is distinctly calcareous in character. 



Summary oy Part III. 



It would be easy to give many more examples of the occurrence of 

 scheelite in situ in lodes, veins, and contact deposits, but it is 

 doubtful if any good purpose would be served by so doing. Enough 

 has been said to show that in very many cases scheelite is found as 

 a lode mineral either with or without wolframite. It is also 

 a frequent product of contact metaniorphism of granites intruded 

 into or near limestones. This metamorphism is of the type commonly, 

 though perhaps unnecessarily, called pneumatolytic. A regular 

 gradation can be traced from the tin- wolfram deposits, through ~the 

 "wolfram deposits without tin to the scheelite lodes. This transition 

 is on the whole accompanied by a falling-off in the amount of the 

 paragenetic molybdenum and arsenic sulphides and the minerals of 

 the fluorine-boron group, but in certain instances tourmaline and 

 fluorite are found to survive into the sciieelite lodes. The genetic 

 connexion between scheelite and siliceous gold veins is also of 

 significance. 



(To be concluded in the next Number.) 



III. — On the Prr-Thanetian Ekosiox of the Chalk in parts, of 

 THE London Basin. 



By Herbert Arthur Baker, B.Sc, F.G.S. 



TT has long been recognized that, in early Eocene times, while the 

 " Calcaire de ^lons" was being deposited in the Belgian area, 

 large tracts of the Upper Chalk were removed by denudation from 

 the south-east of England. The true extent of the unconformity 

 between the Chalk and our oldest Eocene strata is now to be seen 

 only where the Eocene cover yet remains. Even where the Chalk is 



^ The Mineral Industry , vol. xxiv, p. 687, 1916, and vol. xxv, p. 724, 1917; 

 Mining and Scientific Press, May 27, 1916. 

 ^ Scrivener, loc. cit., p. 7. 



