352 report— 1879. 



have frequently the appearance of incipient gneiss. The strike is usually ahout N 

 and S., and it overlies the Dirnetian unconformably. 



4. The Pebidian. This being the newest group in the Pre-Cambrian rocks, is 

 the least altered in character, and most nearly approaches in strike to the overlying- 

 unaltered or Cambrian rocks. It resembles that group in many of its rocks, and on 

 that account was for a time supposed to be identical with it, only that it had 

 undergone local alteration. Now we know it underlies the latter unconform- 

 ably, and that the apparent similarity in character is to be attributed to the fact 

 that most of the Cambrian rocks were derived from the denudation of this group. 

 That it was also in a high state of alteration before the Cambrian rocks were de- 

 posited upon it is evident from the fact that an abundance of pebbles and masses 

 of it occur in the conglomerates at the base of the Cambrian. It consists for the 

 most part of chloritic, felspathic, talcose and micaceous schistose rocks ; alternating 

 with massive and slaty greenstone bands, dolomitic limestone, serpentine, lava-flows, 

 porcellanites, breccias, and conglomerates. It is traversed also frequently by dykes 

 of granite, dolerite, &c. It is a group of enormous thickness, and is largely dis- 

 tributed over Great Britain. It occurs in many parts of Wales, in Shropshire, and 

 in Charnwood Forest. I found it also last year in the North- West of Scotland, and 

 have seen specimens of it, collected by Mr. James Thomson and others, from 

 Islay' and others of the Western Islands. Dr. Hunt recognised it also along the 

 Crinan Canal, and in the vicinity of Lough Foyle in Ireland. It is probably re- 

 presented in America by the Huronian group. The prevailing strike is N.N.E. to 

 S.S W., or from this to N.E. and S.W. The conglomerates at its base are largely 

 made up of masses derived from the Arvonian ; and it is undoubtedly at most of 

 the points examined unconformable to that group. 



6. On some further evidence relating to the range of the Palaeozoic RocJcs 

 beneath the South-east of England. By R. A. C. Godwin- Austen, 

 F.B.8., F.G.S.—See Reports, p. 227. 



7. On ' Culm ' and ' Kulm.' By G. A. Lebour, M.A., F.G.S., Professor 

 of Geology in the University of Durham College of Physical Science, 

 Neivcastle- on- Tyne. 



The word ' Culm,' locally denoting an impure, ' smutty ' kind of coal in the 

 West of England, is now applied by geologists to the series of beds containing 

 this coal in Somersetshire and Devonshire. The horizon of these series is generally 

 admitted to be that of the Millstone Grit, with, perhaps, the uppermost portion of 

 the Upper Carboniferous Limestone series (vide Murchison, Renevier, &c). 



The German geologists, soon after the recognition of the Carboniferous age of 

 the greater part of their so-called ' Jungere Grauwacke ' in 1838, adopted for it the 

 term Culm (spelt JTulni), chiefly, it would appear, on the strength of the charac- 

 teristic fossil Posidmiomya Becheri which is common to these slaty rocks and to 

 the Culm beds of Devon. Under this name of Kulni are now grouped a vast mass 

 of carboniferous slaty beds, which strike across Europe from Eastern Silesia to the 

 westernmost point of Portugal, and include most of the puzzling deposits scattered 

 over Southern and Central France. These were formerly classed as belonging to 

 the vague ' Terrain anthraxif ere,' and as representing in age the entire Lower Car- 

 boniferous series, of which they must be regarded merely as a great altered shaly 

 or non-calcareous facies. 



The following table will show the inequality of the British Culm and of the 

 Continental Kulm : — 



