Professor T. G. Bonnet/ — Eocksfrom Kimherley. 497 



fossils such as we find in Drift gravels in Cambridgeshire, Hunt- 

 ingdonshire, and Hertfordshire. In many places Belemnites and 

 Gryphjeas are preserved when other fossils and fragments of 

 limestone have been dissolved away. Some of these gravels have 

 naturally been used up time after time, and probably only in the 

 later of the gravels, except where protected by Boulder-clay, do we 

 find many pebbles of Chalk or other kinds of limestone. 



in. — On some Eock-Specimens from Kimberlet, South Africa. 

 By Prof. T. G. Bonnet, D.Sc, LL.D., F.E.S., V.P.G.S. 



{Concluded fi-om the October Number, p. 453.) 

 2. Dykes and other Igneous Boclcs. 



ALTHOUGrH not strictly in the order of the title, we may describe 

 first a specimen from the so-called "melaphyre," which forms 

 a great sheet high up in the group through which the diamond - 

 bearing pipes have been driven. This, which bears the label "No. 5, 

 Melaphyre," is nearly 5" in length. Macroscopically, it may be 

 described as a compact dark basalt, showing slight signs of 

 decomposition, and containing rather sparse amygdales of irregular 

 size and shape (the maximum length being about half an inch), 

 filled mostly with calcite and spotted occasionally with dark-green. 

 The specific gravity is 2-842. Microscopic examination shows the 

 following constituents : (a) Plagioclase : microliths of this form 

 a large part of the ground-mass, varying generally from about -005 

 to '007 in length, with a fair number nearly four times this size, but 

 two or three, probably of earlier date, are from four- to six-tenths of 

 an inch. Among these microliths are scattered granules and small 

 grains of iron-oxide ; also a filmy green mineral, exhibiting aggre- 

 gate polarization, but whether it represents a pyroxene or a residual 

 basic glass is not easily determined. Larger grains of augite in- 

 dubitably have been present, which, however, are now replaced by 

 acicular hornblende Avith parallel grouping. In addition to this, 

 needles of this mineral, grouped in tufts, pierce, like pins, into the 

 larger felspars. The latter are not in good preservation ; they con- 

 tain granules of iron-oxide and green specks. Vesicles from about 

 one-twelfth of an inch downwards are found to be fairly numerous : 

 they are now filled by a pale dull-green chlorite, which exhibits 

 pleochroism from an ochre-yellow to a green, giving low polarization 

 tints and apparently straight extinction. Now and then a grain 

 or two of calcite or of epidote may also be present, especially in 

 those of larger size, in which calcite dominates. Other enclosures 

 occur : three wholly included, one, the largest (which cannot have 

 exceeded a quarter of an inch in diameter), almost wholly ; besides 

 two others doubtful in nature because so little is left. Eound each 

 is a slightly interrupted zone of chlorite, usually not more than -01" 

 broad, and sometimes a little calcite. They appear to be quartzite, 

 but the structure is rather peculiar. The inner part consists of 



DECADE IV. VOL. IV. ^NO. XI. 32 



