Professor SuU — On the Glaciation of Norway. 453 



cliaracter of the rock, is probably due to heat ; i.e., is a form of 

 contact metamorphism and in most cases is comparatively slight. 

 1 have not been able to identify any representatives of a glassy or 

 of a minutely crystalline peridotite, and now, after better oppor- 

 tunities of studying rock fragments than on any former occasion, 

 I feel more doubtful than before whether these really occur. The 

 second alteration — that which has produced the external zoning — 

 I attribute to the action of water, possibly at a fairly high tempera- 

 ture, and probably containing in solution some constituents which it 

 obtained during its passage through the surrounding rock.^ 



The difficulty of ascertaining the true nature of this diamantiferous 

 rock mainly arises from the secondary changes which its matrix has 

 undergone ; the principal being infiltration with carbonates and 

 serpentinization. It occurred to me that this might be partially 

 avoided by another method of examination. In the first instance, 

 a small fragment of matrix from Sir W. Crookes' specimen was 

 pulverized, no more force being used than was absolutely necessai-y. 

 The material, after being kept in H CI, in one case for perhaps 

 a quarter of an hour, in another for two days (no difference seemed 

 to result), was mounted for microscopic examination. Mineral 

 grains are fairly abundant ; mostly olivine, with a very few of 

 augite and mica. Their outlines are distinctly those of fragments, 

 not of crystals. This, of course, might be attributed to the force 

 used in breaking up the rock, but as the matrix is barely half as 

 hard as olivine, and great care was taken, I think it improbable 

 that crystals of this mineral would have been much shattered. 

 However, in order to get rid of this difficulty, some other chips 

 from the same specimen and some bits of ordinary soft blue ground 

 (given to me several years ago by Professor Boyd Dawkins) were 

 immersed in HCl (50 percent.). Though the acid was changed and 

 the tubes were frequently shaken, not much powder was detached 

 even at the end of about five months,'^ but the mineral grains in 

 this are identical in shape with those obtained by the other mode of 

 examination. This has materially strengthened my conviction that 

 the " Kimberlite " is in reality a rock of fragmental origin. 



{To he continued.) 



IV. — SiK Henry H. Howorth and the Glaciation of Norway. 

 By Prof. Edward Hull, M.A., LL.D., F.R.S., F.G.S. 



FEW will deny that whatever comes from the pen of Sir Henry 

 Howorth is always interesting and original, whether the reader 

 agrees with it or otherwise. This is especially the case when he 

 has a theory to build up or to overturn, and in the latter case he not 

 only tries to knock over his antagonist, but he discharges at him 



1 I now think it more likely than when I wrote the preface to Professor Lewis' 

 papers, that this has given a serpentinous aspect to certain small fragments which 

 I then conceived might represent a compact or glassy peridotite. 



^ The pieces left" are still too hard to crusli between finger and thumb. This 

 seems to indicate that calcite or dolomite is not the only cement of the rock. 



