248 Professor W. J. SoUas — De7'ived Limestones. 



intra-telluric origin, i.e. concretions of the kimberlitic magmas. 

 They hold the same position to kimberlite as the well-known olivine 

 lumps {oUvhiknollen) , which sometimes have the same rounded-off 

 form and smooth surface, to the basalt in which they are inclosed." 

 To this I reply that: (1) I have spent some time in the endeavour 

 to prove that kimberlite is only a fragmental rock,^ and the 

 occurrence in any peridotite of coarsely crystalline ' concretions ' 

 of garnet, diopside, enstatite, etc., would be without precedent. 

 (2) It has yet to be proved that these ' olivinknoUen ' in basalt 

 are 'concretions,' and I do not envy the man who attempts the 

 task. I have examined scores of them ; they are seldom, if ever, 

 really well rounded, and are, I believe, fragments of a peridotite, 

 caught up by the basalt, as happens to pieces of granite, gneiss, 

 sedimentary and other kinds of rock. If the lumps of eclogite 

 are concretions it is strange they should be so easily separable from 

 the enclosing 'kimberlite,' and still more so that the minerals at 

 their surface should so often be cut through exactly as they would 

 be by attrition. In other words, speaking from a wide experience 

 in the field, I am certain that these are as truly boulders as any 

 in the bed of an Alpine torrent. But Professor Beck, apparently 

 not quite satisfied with his ' concretion ' hypothesis, goes on to 

 suggest that rounding "may be accounted for by a rotatory abrasion 

 during the eruption in the crater." I have examined the materials 

 of a good many volcanic cones, but never saw such perfect rounding 

 as this, and as I foresaw the possibility of that hypothesis being 

 advanced, was careful to insert a sentence to show that I had both 

 considered and rejected it. Thus I find myself unable to admit 

 either the justice of Professor Beck's criticisms or the reasonableness 

 of his hypothesis. The latter, indeed, suggests to me that its 

 inventor has heard the " mouse squeak " more often than " the 

 lark sing." 



HI. — Derived Limestones. 

 By Professor W. J. Sollas, D.Sc, F.E.S. 



MY attention has been directed to the following paragraph, which 

 appears in Mr. H. B. Woodward's monograph on the Jurassic 

 Eocks of Britain, vol. iii, p. 31 (1893). It is as follows :— 



" Prof. Sollas has suggested that rivers sometimes bear to the sea 

 considerable quantities of undissolved calcareous matter, derived 

 from the formation through which they flow. This is a matter 

 that requires confirmation, for it is known that carbonate of lime 

 is more readily soluble in fresh-water than in sea-water." 



The statement attributed to me was more than a mere suggestion, 

 and as the subject is of some interest it may be as well if I now 

 present the evidence which I had in mind when asserting that the 



M do not deny — nay, I expect — that large masses of peridotite (probably 

 also diamantiferous) exist in the crystalline floor, but not ' kimberlite ' as defined 

 by Professor Carvill Lewis. A little lower down, Professor Beck seems to admit the 

 'kimberlite ' to be a breccia. If so, how can it be a ' mas^ma,' unless he means that 

 the unbroken material exists somewhere down below, in which case it is not likely to 

 be ' kimberlite,' but some ordinary variety of peridotite. 



