H. R. B'oworth — Traces of a Great Post-Glacial Flood. 509 



the olivinous tuff by the splitting and attrition of the rock when the 

 tougher particles are rolled and rubbed together till they have a 

 roundish or spherular form ; and secondly, a subsequent application 

 of heat to the tuff, accompanied not uufrequently by the reducing 

 action of gases and vapours. 



The Grosnaja meteorite appears to consist of — 



Silicic acid 33 '78 



3-44 

 ... 28-86 

 3-22 

 ... 23-55 

 ... 0-30 

 ... 0-63 

 0-68 

 ... 0-17 

 ... 5-37 



Alumina 



Iron protoxide 

 Lime 





Magnesia 



Potash 



Soda 



Carbon 



Hydrogen 



Magnetic pyrites ... 





100-00 

 Olivine appears to be the prevailing silicate in the meteorite ; in 

 addition to bronzite there appears to be a little augite and felspar, 

 although their presence could not be recognized. We find, more- 

 over, a small amount of a carbonaceous ingredient, to which, as well 

 as to the magnetic pyrites, the blackish grey colour of the matrix is 

 probably due. 



A plate showing six sections of the mineral constituents of this 

 meteorite accompanies Tschermak's paper. 



{To be continued.) 



I 



VI. — Traces of a Great Post-Glaoial Flood. 

 4. Evidence of the Angular Drift. 



By Henry H. Ho worth, F.S.A. 

 [Continued from the October Number, p. 440.) 

 ET us see then what "the Old Masters" had to say on the subject 

 J before us. In Mantell's Geology of the South-East of England,^ 

 1833, page 28, speaking of the beds of slightly rolled flints which 

 occur on the Downs in Sussex just underneath the turf, he says, "The 

 flints are more or less broken, have suffered but little from attrition, 

 and are so abundant as to form a constant supply for repairing the 

 roads in the south-eastern part of Sussex. This bed has clearly been 

 formed by the destruction of the upper portion of the chalk ; and it 

 is equally evident that the cause which produced the disintegration 

 of the superior strata was as transient as it loas effective, since, 

 although the chalk in which the flints were imbedded has been 

 entirely destroyed, the latter have sustained but very little injury'." 

 In 1839 Sir Henry De la Beche published his masterly report 

 on the Geology of Cornwall, Devon, and West Somerset. In this 

 admirable work he discusses inter alia the origin of the gravels and 

 other superficial detritus in which stream-tin occurs. He argues 

 strongly against the marine or fluviatile origin of these gravels. 

 Speaking of the valleys in which they occur, he says that if, previous 

 to the drift of the tin-stone pebbles, they had been beneath the sea, 



